CARESA PHYSICS TRIAL 1

PART A: 1A, 2D, 3A, 4A, 5B, 6C, 7D, 8B, 9A, 10B, 11D, 12A, 13B, 14B, 15C.

 

PART  B

 

The marks allocated to each question are shown.

Answer this Part in the spaces provided in your examination book

Show all necessary working.

Marks may be awarded for relevant working.

 

16.              Pluto has a mass of 0.002 that of Earth and a radius 0.18 that of Earth.

(i)                 What is the value of the acceleration due to gravity on the surface of Pluto?

(2 marks)

 

g = GM/r2        gp = gE GMp/rp2  x rE2 / GME    = 9.8 x 0.002 / 0.182 = 0.6 ms-2

 

(ii)               What would be the escape velocity from the surface of Pluto? (2 marks)

 

½ mv2 = GmMp/rp       v2 = 2GMp / r p                                                                        = 2 x 6.67 x 10-11 x 0.002 x 6 x 1024 / 0.18 x 6.38 x 106    v = 1180 ms-1

 

17.              The orbital velocity of a satellite in a stable orbit decreases as the distance from the centre of the Earth increases. Why is it that as a satellite slows down due to friction with low-density air, its distance from the centre of the Earth decreases as its orbital velocity decreases? (2 marks)

 

A satellite has to increase its potential energy to change from a low orbit to a higher one. Although it requires less kinetic energy to provide the centripetal force, its total energy (potential + kinetic) has increased. When a satellite slows due to friction its kinetic energy decreases and can’t provide the centripetal force. With gravity providing a stronger force than the centripetal force the satellite slowly spirals to lower and lower orbits.                                     

18.       (i) A space probe to Jupiter sometimes takes a path in the opposite direction  so that it      swings around Venus to gain speed. What is the name of this maneuver? (1 Mark)

 

The slingshot effect

 

(ii) Newton’s Universal Law of gravitation is defined as F = Gm1m2 /d2. Discuss its importance in understanding the motion of satellites. (2 Marks)

 

Gravity provides the centripetal force that keeps satellites in motion around the Earth. Newton’s Universal Law of Gravitation enables quantitative values of the gravitational force acting on satellites to be determined so that the correct height and speed of a satellite can be calculated for optimum performance.

 

 

 

 

19.       Describe the method used by Michelson & Morley in their attempt to measure the relative velocity of the Earth through the aether. (3 marks)

 

Michelson & Morley shone monochromatic light onto a half silvered mirror, inclined at 45o to the light, so that about half of the light passed through the mirror, and the other half was reflected at 90o to the first. The two beams travelled approximately the same distance and were reflected back by plane mirrors at right angles to the beams. The two beams were recombined and formed an interference pattern of alternating bright and dark bands.

Michelson & Morley rotated their apparatus, expecting to see changes in the interference pattern as the beam that was originally travelling parallel to the aether was now travelling perpendicular to the aether and vice-versa. No such change was detected.

 

20.       Describe a thought experiment involving mirrors and trains and discuss the relationship between thought and reality. (5 marks)

 

                 

Suppose A & B are equidistant from observer O on a train moving with velocity v. Suppose also that A & B have mirrors so that they reflect a flash of light made by observer O. Observer O will see the flash reflected simultaneously from A & B so that from O’s frame of reference the two reflections are simultaneous.

For an outside observer O`, because the train has moved forward in the time it takes the light to reach A & B, the reflection from A will travel a shorter distance than the reflection from B so from O`’s frame of reference the events are not simultaneous; A’s reflection will occur before B’s.

This thought experiment suggests that time passes at different rates from different frames of reference. Although this idea seems intuitively wrong it has been verified in reality by examining the half-life of fast moving muons from outer space and from studies of twin atomic clocks in different frames of reference.                                    

21.       A spaceship which has a mass of 100 tonnes (105 kg) on Earth is travelling at 0.90c.

(i) What is its mass as observed by someone on Earth? (1 mark)

 

MV = Mo / \/(1 – v2/c2)             = 105 / \/(1 – 0.92)        = 2.29 x 105 kg

 

(ii) How much work is required to accelerate the spaceship from 0.90c to 0.95c?                (2 marks)

 

Initial Ek = ½ x 2.29 x 105 x (0.9 x 3 x 108)2   = 8.347 x 1021 J

            Final mass = 105 / \/(1- 0.952)              = 3.20 x 105kg

                        Final Ek = ½ x 3.20 x 105 x (0.95 x 3 x 108)2 = 1.30 x 1022 J

                        Work done = 1.30 x 1022  - 8.347 x 1021 = 4.65 x 10 J

 

 

 

 

 

22.       This question refers to the following diagram.

 

           

A rectangular coil WXYZ is 20 cm long and 10 cm wide as shown. The coil has 200 turns of wire and lies parallel to a uniform magnetic field of 0.2 Tesla. A current of 5.0 amps flows through the coil in the direction WXYZ.

(i)                 Calculate the force on a single wire on the side WX.  (2 marks)

 

F = BIl            = 0.2 x 5.0 x 0.2          = 0.2 N into page

 

(ii)               Calculate the torque due to the force on a single wire on the side WX.  (1 mark)

 

Torque = Fd    = 0.2 x 0.05     = 0.01 Nm anticlockwise from WZ

(iii)             Calculate the total torque on the coil.  (1 mark)

 

Torque = BAIn cosq   = 0.2 x 0.1 x 0.2 x 5 x 200 x cos 0o    = 4 Nm anticlockwise from WZ

23.       (i)         With the aid of a diagram, explain how induction is used in cooktops in electric

 ranges.  (2 marks)

 

                                   

Coils underneath the glass or ceramic cooktop have alternating current flowing through them. The changing magnetic field produced by the alternating current cuts the base of a metallic saucepan and induces eddy currents in its base. The eddy currents produce heat in the base of the saucepan so that the saucepan gets hot but the cooktop doesn’t.

 

(ii)               State one way in which induction electric cooktops are safer than conventional electric cooktops. (1 mark)

 

The ceramic cooktop doesn’t get hot so people will not burn themselves.                

(iii)             William placed three saucepans of water on his new induction cooktop. After a few minutes the water in the cast iron saucepan was boiling furiously, the water in the aluminium saucepan was lukewarm and the water in the glass saucepan was cold. Explain why the water in the different saucepans heated by different amounts.  (2 marks)

 

The cast iron saucepan is magnetic so becomes a magnet when cut by the magnetic field produced by the coil. Because the magnetic field is enhanced it produces high eddy currents when cut by a changing magnetic field. The aluminium saucepan is non magnetic and because of the reduced magnetic field produces low eddy currents. The glass saucepan was a non-conductor of electricity so did not produce any eddy currents.

 

24.       Electricity is carried through transmission lines at high voltage to minimise energy loss. Explain how a high voltage will reduce energy loss.  (3 marks)

           

The resistance of the transmission wires is constant. Since a lower voltage means a higherer current and the power loss in the lines is given by P = RI 2 then a higher current means a much higher power loss as energy is converted to heat in the transmission wires and this heat is lost to its surroundings. There is also some energy loss in induction as the changing magnetic field produced by the alternating current cuts external conductors. The higher the current in the transmission lines then the higher the magnetic flux and the higher the power loss due to eddy currents in nearby conductors. A high voltage results in a low current.

 

 

25.       Describe how you could perform an investigation to model the generation of an electric current by moving a magnet in a coil or a coil near a magnet. Include a table showing possible results for the variables that you are investigating.  (8 marks)

 

Connect a coil to a galvanometer. Insert a magnet, north-pole first, into the coil at a slow rate. Record the reading on the galvanometer. Now insert the magnet, north-pole first, into the coil at a fast rate and record the reading on the galvanometer. Repeat the procedures inserting the magnet south-pole first. Now repeat each of the four procedures twice so that a total of three readings is obtained for each situation.

 

Typical Table of Galvanometer Readings

                                                           

Galvanometer reading (mA)

North Pole First: Fast

60

50

55

North Pole First: Slow

30

25

25

South Pole First: Fast

-65

-55

-55

South Pole First: Slow

-25

-20

-30

 

 

 

 

 

 

 

 

 

 

 

 

26.       Prior to Thomson’s experiment in which he measured the charge to mass ratio of cathode rays, there was debate among scientists such as Hertz and Crookes as to whether cathode rays were particles or electromagnetic waves. Compare the evidence suggesting that cathode rays were particles with that suggesting that they were electromagnetic waves.  (4 marks)

 

Hertz thought cathode rays were waves because;                                                     

He did not detect any deflection of cathode rays by electric fields. (The ones he used were too weak)

Cathode rays cause fluorescence in some reactions.

Cathode rays were able to penetrate thin layers of metal without damaging the metal.

Crookes thought cathode rays were particles because;                                  

Cathode rays were deflected by magnetic fields.

The speed of cathode rays was measured as being less than that of light.

Cathode rays can cause a small paddle wheel to rotate, showing that they have momentum.

A target that had been bombarded with cathode rays attained a negative charge.

 

27.               (i)        Describe Hertz’s observation of the photoelectric effect.  (2 marks)

                       

Hertz used an induction coil to obtain the high voltage to produce a spark across a gap. He used a parabolic mirror to reflect any waves towards a receiving antenna a few metres away. The receiving antenna consisted of a wire loop with a spark gap at the focus of a second parabolic mirror. The spark across the transmitting gap produced waves that caused sparks to be produced across the receiving gap. Hertz shone ultraviolet radiation onto the detecting loop and found that he produced a brighter spark. He also found that when he shone U.V. radiation onto the detecting loop he was able to produce a spark across a wider gap.

 

(ii)        Explain how the photoelectric effect suggests that light consists of particles.  (3 marks)

 

Classical theory predicts that there would be a delay between the time the low intensity light began to shine on the surface and the emission of photoelectrons. Einstein proposed that light energy was concentrated in tiny bundles (photons), each having energy given by E = hf. If a photon had sufficient energy to release a photoelectron then it would transfer all of its energy to the photoelectron.

 

28.              Compare the passage of electrons through aluminium at room temperature to that through aluminium below its critical temperature of 1.2K.  (4 marks)

                                

At room temperature atoms in a metal are arranged in a crystal lattice and the spacing between the atoms is so close that the valency electron orbits overlap so that they are shared between the atoms. If a potential difference is applied to a wire, the electrons will experience a force in the direction opposite to the electric field. This will increase the rate of collisions between other electrons and ions within the crystal lattice. This will cause the ions to vibrate faster (i.e. they are hotter), increasing the rate of collisions and hence resistance.

Below the critical temperature the crystal lattice distorts and emits a phonon that forms a region of positive charge behind the electron. This attracts the electron behind it to form a pair known as a Cooper pair. There is a transfer of a phonon from the first to the second electron and it is this transfer of phonon energy that keeps the Cooper pairs together. They are not permanent bonds and Cooper pairs keep breaking up and reforming. There are no collisions with impurities or the crystal lattice and so there is no resistance.

 

29.       How many photons of wavelength 600 nm would be required each second to produce a power output of 5 W?  (2 marks)

 

Energy of each photon = hf = hc/l = 6.63 x 10-34 x 3 x 108 / 600 x 10-9 = 3.315 x 10-19 J

   Number of photons = 5/3.315 x 10-19 = 1.51 x 1019 photons/second                                     

 

30.       Describe how superconductors and the effects of magnetic fields have been applied to develop a maglev train.  (3 marks)

 

The E.D.S. (electrodynamic suspension) system in Japan uses the opposing force between superconducting magnets on the train and conventional electromagnets in the guideways (rails) to levitate it. The superconducting loops are made of niobium/titanium alloy and are cooled with liquid nitrogen. It begins to levitate once it reaches 40 km/h.

The E.M.S. (electromagnetic suspension) system in Germany uses conventional electromagnets under the train and also in the guideways. The like polarities cause the train to lift.

Both trains are propelled by the continually changing polarity of alternate magnets along the track.          

 

31.       Assess the impact of transistors on society with particular reference to their use in microchips and microprocessors.  (2 marks)

 

The development of the transistor has allowed electronic components to be made a lot smaller and a lot cheaper than thermionic devices. In the 1960s computers would occupy a large room and cost millions. Today the average family has their own personal computer with more power than the 1960s model, at a fraction of the cost and small enough to fit on a desktop. This has been made possible by the development of microchips and microprocessors, both of which use miniature transistors. Navigation systems can now be preset making navigation easier and more accurate. This has led to safer aircraft operation. Microprocessors in automatic teller machines and at EFTPOS outlets enable money to be transferred in an instant while still keeping accurate records of accounts. In biotechnology it has led to the mapping of the human genome- impossible without the use of microprocessors.

 

 

 

 

 

 

 

 

 

 

 

 

OPTIONS.

 

ATTEMPT ONE OPTION ONLY

 

Each option is worth 25 marks.

 

 

 

 

 

 

ASTROPHYSICS

 

Attempt All parts of this question.

 

32.       (i)         Calculate the distance in parsecs of a star that has a trigonometric parallax of   

                        0.01 seconds of arc.  (1 mark)

                        d = 1/p             = 1/0.01           = 100Pc.

 

(ii)        Outline how adaptive optics, interferometry and active optics can improve the resolution and/or sensitivity of ground-based telescopes.   (3 marks)

 

Adaptive optics uses a wavefront sensor to feed signals into a computer that corrects for atmospheric turbulance. It uses such devices as tip-tilt mirrors and deformable mirrors, both of which are subject to hundreds of computer directed adjustments per second.

            Interferometry combines data from several sources to improve resolution. Several antenae of radio telescopes for instance, may combine data to form interference patterns that are analysed by computers.

            Active optics uses a computer feedback system that corrects sagging and other deformities in the mirrors of reflecting telescopes.

 

(iii)       Suppose you used an accurate spectroscope to examine light from the Sun, a tungsten filament lamp (normal light globe) and mercury vapour lamp. Outline the ways the spectra from these three sources would differ.   (3 marks)

 

The Sun appears to produce a continuous spectrum but closer inspection reveals hundreds of dark lines (Fraunhaufer lines) due to the absorption spectrum of the elements in the Sun. The tungsten filament lamp is a hot solid and produces a continuous spectrum whereas the mercury vapour lamp is a hot gas and pruduces an emission spectrum consisting of lines of characteristic wavelengths on a black background.

 

(iv)       Compare the spectrum produced by a galaxy to that produced by a star such as the Sun.  (2 marks)

                       

A galaxy does not have a cool outer layer so it will produce a continuous spectrum. All wavelengths of the electromagnetic spectrum will be present. The galaxy is also likely to show a red shift as it is receding (although a few, such as Andromeda, are approaching and show a blue shift).

Stars consist of a very hot, dense core of gas that produces a continuous spectrum. However, they are surrounded by a cooler layer of gas on the surface. The low pressure gaseous atoms will absorb radiation at their characteristic spectral wavelengths and re-radiate it in all directions as the electrons return to their previous levels. The result is a continuous spectrum with dark lines crossing it at the characteristic wavelengths for the elements present at the surface of the star. i.e. an absorption spectrum.

 

(v)        Hadar (b-Centauri) has an apparent magnitude of  0.60 and is 390 Pc away. What is its absolute magnitude?   (2 marks)

m-M = 5 log d/10        0.60 – M = 5 log 390/10 = 5 log 39 = 7.96                            

-M = 7.96 – 0.60 = 7.36          M = -7.36                                                                   

Note that the distance to Hadar is incorrect in the question. It is actually 390 L.Y. (120 Pc) away.

 

(vi)       What is photometry?  (1 mark)

                       

Photometry is the measurement of light intensity and amounts of illumination.

 

(vii)      What advantages do photoelectric technologies have over photographic methods of photometry?   (2 marks)

Photoelectric techniques are able to take precise measurements of the amount of light reaching us from a star. It tells us the total amount of radiation above the threshold frequency of the photocell that is reaching us. Photographic techniques have the problem that films are not equally sensitive to all wavelengths. Consequently a star may seem brighter because the film is sensitive to the wavelength of the light that it produces whereas a dimmer star may be sending us more radiation but not at the film’s optimum wavelength.

(viii)     Distinguish between astrometric binary stars and spectroscopic binary stars. 

(2 marks)

Astrometric binaries are identified by the perturbations (wobbles) in the orbit of a star as it is affected by the gravity of an unseen companion.

The two stars in a spectroscopic binary can be identified by their red and blue shift. One star will exhibit a red shift as it moves away while the other exhibits a blue shift as it moves towards us. Half a period later the red and blue shift of the two stars is reversed.

 

 

(ix)             Omega Centauri is a globular cluster and Kappa Crucis (also known as the Jewel Box) is an open cluster. In what ways would these two clusters be different?          

(3 marks)

                       

The globular cluster, Omega Centauri, would be situated in the galactic halo and have over 100 000 stars. These stars would be first generation, old stars. There would be no O or B class stars and there would be a large number of red giants.                     

The open cluster, Kappa Crucis, would be in the galactic plane and have a few (10 to 1000) stars, all relatively young. Open clusters show a high concentration of metals, which indicates that they are second or third generation stars.

 

 

 

 

 

 

 

 

 

(x)        With reference to the H-R diagram, discuss differences in the evolutionary track of stars of 1, 5 and 10 solar masses.  (6 marks)

 

Stars form from the clouds of hydrogen and dust that are found between stars in the galactic plane. For some reason such as shock waves from a supernova or a star passing nearby, regions of higher than average density form and these in turn attract more atoms and the cloud condenses to a size somewhere around that of the Earth’s orbit in around 50 years. The more massive the cloud the shorter is the time of condensation. The gravitational collapse  causes the centre of the gas cloud to heat up and produce radiant energy and this slows the gravitational collapse. During this phase which is typically 100 000 years for a 10 s.m. star, a million years for a 5 s.m. star and 50 million years for a 1 s.m. star, the core of the protostar increases its temperature until at about 10 million kelvin, hydrogen fusion begins and the star enters the main sequence region on the H-R diagram. The more massive stars enter the main sequence stage at a higher position on the H-R diagram. A 10 s.m. star would be a B class star, a 5 s.m. an A class and a 1 s.m. would be a G class star.

During their time on the main sequence the stars become a little hotter and more luminous so their position on the H.R. diagram moves a little upward to the left. A 1 s.m. star would produce its energy mostly from the proton-proton reaction while the more massive stars would produce their energy by the carbon cycle. The more massive stars burn more furiously and use their core hydrogen more quickly than smaller stars. Consequently they spend less time as a main sequence star. A star of 10 s.m. will spend about 10 million years  as a main sequence star, a 5 s.m. star about 100 million years while a 1 s.m. star will spend about 10 billion years as a main sequence star.

When the hydrogen in the core has been consumed then shell burning will commence and the star will expand due to an increase in radiation pressure. The stars will move upwards and to the right on the H-R diagram. During this phase the core of the star contracts and becomes hotter while the outside of the star expands and becomes more luminous and cooler.  Eventually the core temperature reaches around 100 million kelvin and helium fusion to form carbon begins. At this stage the size and colour of a 1 s.m. star would classify it as a red giant while the bigger 5 s.m. and 10 s.m. stars would be classified as red supergiants.

Helium fusion is the last nuclear reaction for the 1 s.m. stars. When the core helium has been used up the star will contract and heat up due to gravity. As it does so it will dim to become a very hot and very dense white dwarf. White dwarfs are found on the lower left of the H-R diagram. The outer layers of the red giant may remain behind as it contracts and become a planetary nebula and drift off into space.

For the 5 and 10 s.m. stars the exhaustion of helium means that the core contracts further and becomes hotter. At about 600 million kelvin the fusion of carbon to form heavier elements begins. As the carbon is used up the heavier elements fuse into still heavier elements. The result is a series of concentric shells with elements increasing in atomic number from the outside to the core. As the stars undergo these reactions they pass in and out of a region between the suoergiants and the main sequence called the instability strip. At this stage the stars are pulsating variables.

When the core of a supergiant becomes iron then further nuclear fusion to heavier elements becomes endothermic. This results in a rapid cooling and contraction in the core of the star. The outer layers rush in and heat very rapidly. The result is a huge stellar explosion; a supernova. The outer layers of the star are blown into space to form a nebula. The core of a 5 s.m. star will contract to form a neutron star while that of a 10 s.m. star will contract to form a black hole, matter so dense that even light cannot escape from its surface.

 

 

 

 

 

 

 

 

 

 

FROM QUANTA TO QUARKS

 

Attempt All parts of this question.

 

33.       (i)          Describe the Rutherford model of the atom.   (1 mark)

 

Rutherford described the atom as having a small, positively charged nucleus that contained most of the mass of the atom. Electrons orbited the nucleusat a large distance so most of the atom is empty space. The centripetal force is provided by the electrostatic attraction between the electrons and nucleus.

 

(ii)        The limitations of classical physics gave birth to quantum physics. What is the difference between classical physics and quantum physics?  (2 marks)

                 

Classical physics includes Newtonian mechanics and treats electromagnetic waves as being continuous quantities rather than being ‘packets’ of energy. It covers developments to around the end of the 19th century. Quantum physics takes a relativistic view of mechanics and treats electromagnetic waves as discrete ‘bundles’ or quanta of energy.

 

(iii)       Hydrogen shows a large number of spectral lines, the visible ones being part of the Balmer series where nf = 2.

Calculate the frequency of radiation emitted when an electron drops from ni = 3 to nf = 2 and also from ni = 10 to nf = 2.

                        What type of radiation is emitted by the drop from ni = 10 to nf = 2?    (3 marks)

 

            1/l = R {(1/nf)2 – (1/ni)2}       

1/l = 1.097 x 107{(1/2)2 – (1/3)2}       l = 6.563 x 10-7 m.     

 

            1/l = 1.097 x 107 {(1/2)2 – (1/10)2}    l = 3.798 x 10-7 m.

            Ultraviolet radiation is emitted when an electron drops from ni = 10 to nf = 2.

 

 (iv)      What was de Broglie’s proposal and how was it confirmed by Davisson and Germer?  (3 marks)

Louis de Broglie proposed that all waves have some particle properties and that all particles have some wave properties.            

Davisson and Germer demonstrated electron diffraction patterns and thus showed that electrons have a wave nature. They reflected electrons off the surface of a nickel crystal and found that certain angles produced diffraction patterns.

 

(v)        How fast would an electron be moving if it had a wavelength of 10-10 m?

(2 marks)

 

 l = h / mv       v = h /ml         = 6.626 x 10-34 / (9.109 x 10-31 x 10-10)                                    = 7.274 x 106 ms-1

 

 

(vi)             Describe Fermi’s initial experimental observations of nuclear fission. (3 marks)

 

After the neutron was discovered, Fermi began the systematic bombardment of elements with neutrons. He found that slow neutrons were more effective in initiating nuclear reactions than fast neutrons. Following the discovery of nuclear fission by Hahn and Strassmann, Fermi bombarded Uranium with neutrons and found that the products of the reaction varied. He found that more neutrons were released from the reaction than were used to initiate it. He investigated chain reactions and neutron absorbers and in 1942 produced the first controlled nuclear chain reaction.

 

(vii)           Name a radioactive isotope used in agriculture and describe its use.  (2 marks)

 

                        Carbon-14 can be used to trace the pathways of biological reactions such as photosynthesis in agriculture. The plant is exposed to carbon dioxide made up of the carbon-14 isotope. By analysing different parts of the plant for carbon-14 it is possible to determine the pathway of carbon dioxide through the plant and to develop more efficient growth patterns.

 

(viii)     Neutron scattering is a method used to study the structure of matter. Discuss the advantages and limitations of neutron scattering.  (3 marks)

 

Neutrons have no charge and so are not repelled by atomic nuclei. The de Broglie wavelength of thermal neutrons is approximately the same as the atomic spacing in crystal lattices and their energy is similar to that of lattice vibrations. The magnetic moment of neutrons can be used to study nuclear magnetic properties. Unfortunately a high flux nuclear reactor is required to provide sufficient neutrons and this limits the application of neutron scattering on the grounds of cost and safety concerns.

 

(ix)       Outline the key features and components of the standard model of matter. 

(6 marks)

 

The standard model of matter refers to the explanation of the structure of matter in terms of fundamental particles. The particles in the standard model are quarks and leptons and each of these comes in six varieties or “flavours”. Matter as we know it is composed of up & down quarks, electrons and electron neutrinos. These are known as first generation particles. Second and third generation particles are only found at very high temperatures and in energetic nuclear disintegrations. These particles are unstable and decay into first generation particles. For each particle there is a corresponding antiparticle. A third group of particles, called bosons, also exists and these are force-carrying particles that are responsible for the four force fields.

Quarks carry a charge of +2/3 e or –1/3 e and combine to form hadrons. Hadrons   are subdivided into baryons (3 quarks) and mesons (quark + antiquark). Hadrons are held together by the strong nuclear force between quarks.                                    

Leptons have little or no mass and interact through the electromagnetic force and the weak nuclear force.                                                  

Bosons carry forces between particles. The strong nuclear force is carried by the gluon, the weak nuclear force by W & Z bosons, the electromagnetic force by photons and the gravitational force by gravitons.

 

 

 

 

 

 

 

 

MATTER

 

Summary of types of particles.

 

 

                                                                                    PARTICLES

 

 

 

 

 


                                                HADRONS                                                    LEPTONS

                                                            Experience strong nuclear                               Do not experience strong

                                                            force.                                                               nuclear force.

                                                            They are made up of quarks.                           They are fermions with

                                                                                                                                    ½ integer spin and obey the

                                                                                                                                    Pauli exclusion principle.

                                                           

 

 

                                                MESONS                                           BARYONS

                                    Mesons have                                                   Baryons are fermions with

                                    zero or integer spin.                                         ½ integer spin.

                                    They do not obey the                                      They obey the Pauli

                                    Pauli exclusion principle.                                exclusion principle.

                                    Composed a quark & antiquark.                     Composed of 3 quarks.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

            ii.                                                                  The diagram below represents one loop of a coil in a simple D.C. electric motor.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Which of the following graphs shows the relationship between the force on the side WZ and time for one revolution of the coil WXYZ from its initial horizontal position?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

a.                                           A wire is connected in a circuit and a current flows through it. If the potential difference across the circuit is increased so that more current flows through the wire, what happens to the drift velocity of the electrons?

 

A.    It increases.

B.     It decreases.

C.     It remains the same.

D.    More information is required to determine what happens to the drift velocity.

 

 

 

 

 

 

 

 

 

 

 

 

 

          iii.                                                                  The following diagram represents three parallel wires, X, Y and Z carrying currents of 5A, 5A and 10A respectively in the same direction.

 

 

 

 

 

 

 

 


                             X         Y                     Z

 

 

            The separation between X and Y is 10 cm and between Y and Z is 20 cm.

            What is the direction of the force on wire Y, the middle wire?

 

(a)    To the left.

(b)   To the right.

(c)    Into the page.

(d)   None as the net force is zero.

 

 

iv.                                                                                    Why is an electric motor more likely to burn out when it jams rather than when it is running freely?

 

(a)    The back e.m.f. produces an increase in current.

(b)   The coil has less resistance when it is not moving.

(c)    Eddy currents cause the coil to heat up.

(d)   The net potential difference across the coil increases.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

v.                                                                                    A potential difference is applied to two metal plates as shown. Y is a point midway between the plates and X is midway between Y and the positive plate.

 

 

 

 

 

 

 

            Which of the following statements is correct?

 

(a)    The electric field strength at X is greater than the electric field strength at Y.

(b) The electric field strength at X is less than the electric field strength at Y.

(c) The electric field strength at X is the same as the electric field strength at Y.

(d) It depends on the voltage between the plates whether the electric field strength at X or Y is greater.

 

vi.                                                                                    Which of the following represents the property of a superconductor in a strong magnetic field?

 

(a)    It has a higher critical temperature than with no magnetic field.

(b)   It has a lower critical temperature than with no magnetic field.

(c)    It will itself exhibit stronger magnetic field.

(d)   It will lose its superconducting qualities.

 

vii.                                                                                    The resistance of conductors and semiconductors changes with temperature. Which of the following situations occurs when the temperature increases.

 

 

Semiconductor e.g. Si

Conductor e.g. Cu

A

Resistance increases

Resistance increases

B

Resistance increases

Resistance decreases

C

Resistance decreases

Resistance increases

D

Resistance decreases

Resistance decreases

 

viii.                                                                                    In 1915 W. H. Bragg  and his son W. L. Bragg  were awarded the Nobel Prize for their analysis of crystal structure by diffraction techniques.

What kind of beams did they use in their experiment?

 

(a)    Light

(b)   X-rays

(c)    Electrons

(d)   Radio waves

 

 

 

 

15.    A television screen produces a picture by scanning a beam across the picture tube.

         What are the beams composed of?

 

(a)    High frequency electromagnetic waves.

(b)   Low frequency electromagnetic waves.

(c)    Light rays

(d)   Cathode rays

 

16.        In 1875 Sir William Crookes used a cathode ray tube containing a Maltese Cross and produced a shadow of the cross on the front of the tube.                                             

What did this experiment demonstrate about cathode rays?

 

(a)    Cathode rays are particles.

(b)   Cathode rays travel in straight lines.

(c)    Cathode rays have an electric charge.

(d)   Cathode rays are electromagnetic radiation similar to light.

 

17.       A beam of electrons is deflected as it passes through an electric field as shown.

 

 

 

 

 

 

 

 

 

What would be the direction of a magnetic field that would act with this electric field to let the beam of electrons pass through undeflected?

 

(a)    Towards the top of the page.

(b)   Towards the bottom of the page.

(c)    Into the page.

(d)   Out of the page.

 

 

 

 

 

 

 

 

 

 

17.              This question refers to the following diagram.

Hertz found that when he applied a high voltage across a spark transmitter he was also able to produce sparks in a receiver loop.

By shining U.V. rays onto the receiver loop the intensity of the spark in the receiver loop was increased.

What was the reason for the increased intensity of the spark in the receiver loop that was produced by the U.V. rays?

 

(a)    The photoelectric effect.

(b)   Thermionic emission.

(c)    Increased radio waves.

(d)   Electron diffraction.

 

18.              Two experimental cavity radiators were constructed to approximate the performance of black bodies. The shape and size of the radiators were identical but different materials were used for each cavity radiator. The first radiator was made of copper and the second was made of aluminium. Copper is a better thermal conductor and also a better electrical conductor than aluminium.

 

 

 

 

 

 

 

 

 

Which of the following statements correctly describes the radiation emitted from each radiator when each is heated to the same temperature?

 

(a)    No radiation would be emitted from either hole as they are both black bodies.

(b)   The radiation emitted from the copper would have a longer wavelength than that emitted from the aluminium.

(c)    The radiation emitted from the copper would have a shorter wavelength than that emitted from the aluminium.

(d)   The radiation emitted from both radiators would be identical.

 

19.              Yellow light is found to emit photoelectrons from a metal with kinetic energy Ek and current I.  What will be the effect on the kinetic energy of the photoelectrons and on the current if the intensity of the yellow light is increased so that it is brighter?

 

 

Kinetic Energy Ek

Current I

A

Same

Same

B

Increase

Same

C

Same

Increase

D

Increase

Increase

 

 

20.              Germanium was used to manufacture early transistors whereas silicon is used to manufacture present day transistors.      

What is the reason that silicon was not used in early transistors?                                                                             

(a)    Technology had not been developed that enabled silicon to be used in transistors.

(b)   Germanium was less expensive than silicon.

(c)    Germanium was used in thermionic devices that transistors replaced.

(d)   Silicon could not be obtained in sufficiently pure form.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NAME: ……………………………………….

 

 

PART  B

 

The marks allocated to each question are shown.

Answer this Part in the spaces provided in your examination book

Show all necessary working.

Marks may be awarded for relevant working.

 

21.              A trip to a fun park with a roller coaster is much less expensive than a rocket launch.  Compare the forces acting on an astronaut during launch with the forces acting on a person during a roller coaster ride. (3 marks)

 

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22        Describe a simple experiment you could perform to determine if you were in an inertial frame of reference.  (2 marks)

 

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23.              What is the difference between Einstein’s theory of general relativity and his theory of special relativity.  (1 mark)

 

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24.              The importance of the Michelson-Morely experiment was its null result. What is the role of such an experiment in making determinations about competing theories.           (2 marks)

 

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25.              One of the most dangerous parts of a space flight is the re-entry into the Earth’s atmosphere.

Discuss issues associated with safe re-entry into the Earth’s atmosphere. (3 marks)

 

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26.              With reference to Lenz’s law explain why an electric motor or generator can never be 100% efficient. (2 marks).

 

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27.              What is the role of transformers in electricity sub stations?  (1 mark)

 

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28.              The diagram below shows a moving coil meter.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Describe the principles of the moving coil meter that enable it to measure the current flowing through a circuit. (5 marks)

 

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29.              A D.C. motor requires a commutator to operate effectively.  Describe the construction and operation of the commutator in a typical D.C. electric motor. (4 marks)

 

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30.       Discuss how semiconductors can be used to make solid state components that replace thermionic devices and describe the advantages of these solid state components.            (5 marks)

 

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31.              In 1892 the German scientist Heinrich Hertz was of the opinion that cathode rays were electromagnetic radiation yet British scientists a few years later demonstrated that they were particles.

Discuss the evidence that suggested that cathode rays were electromagnetic radiation and outline the experimental evidence that caused scientists to conclude that they were particles. (5 marks)

 

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32.              Describe the differense between conductors, semiconductors and insulators in terms of band structures and relative electrical resistance. (3 marks)                                                           

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33.       Discuss Einstein’s and Planck’s debate about whether science research is removed from social and political forces. (3 marks)

 

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34.              Tin is a fairly good conductor but becomes a superconductor below its critical temperature of about 3.7K. Outline how the lattice of tin impedes the path of electrons causing heat to be generated but below 3.7K electrons pass through unimpeded with no energy loss. (4 marks)

 

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NAME:………………………………….

 

TEACHER:……………………………..

 

FORT STREET HIGH SCHOOL

TRIAL  HIGHER  SCHOOL  CERTIFICATE EXAMINATION

2001

PHYSICS

2 UNIT

ANSWER BOOK

 

*Part A           20 multiple choice questions, each worth 1 mark.

Choose the best answer from the alternatives offered and indicate your choice by shading in the appropriate spaces below.

 

            A         B         C         D                                             A         B         C         D

Q.1.     0          0          0          0                                  Q.11.   0          0          0          0

 

Q.2.     0          0          0          0                                  Q.12.   0          0          0          0

 

Q.3.     0          0          0          0                                  Q.13.   0          0          0          0

 

Q.4.     0          0          0          0                                  Q.14.   0          0          0          0

 

Q.5.     0          0          0          0                                  Q.15.   0          0          0          0

 

 

 

Q.6.     0          0          0          0                                  Q.16.   0          0          0          0

 

Q.7.     0          0          0          0                                  Q.17.   0          0          0          0

 

Q.8.     0          0          0          0                                  Q.18.   0          0          0          0

 

Q.9.     0          0          0          0                                  Q.19.   0          0          0          0

 

Q.10.   0          0          0          0                                  Q.20.   0          0          0          0

 

 

 

OPTION: FROM QUANTA TO QUARKS

 

(a)        James Chadwick is credited with discovering the neutron yet the experiment that led to its discovery was first performed by Frederic and Irene Joliot.

Outline how Chadwick interpreted the Joliot experiment to verify the existence of the neutron. (3 marks)

 

(b)               Name a nucleon that has no charge. (1 mark)

 

(c)                In 1930 Wolfgang Pauli predicted the existence of the neutrino yet it was not actually detected until an experiment by Cowan and Raines in 1956.

What led Pauli to predict the existence of the neutrino? (3 marks)

 

(d)       Define the term “transmutation”. (1 mark)

 

(e)        In 1808 John Dalton wrote; “Atoms of different elements cannot be changed from one into the other.”

Evaluate this statement with reference to the beta decay of carbon-14. (2 marks)

 

(f)        A student said to you that the protons in the nucleus were held together by gravitational attraction that just balanced the electrostatic force of repulsion.  With reference to the relative contributions of electrostatic and gravitational forces between nucleons explain why you would disagree with the statement. (2 marks)

 

(g)        How do the properties of the strong nuclear force vary with distance between nucleons.

Draw a graph (numerical values not required) to show this relationship. (3 marks)

 

(h)        An atom bomb and a nuclear reactor both produce nuclear reactions, but whereas the first is an uncontrolled, fast reaction the second is a controlled, much slower reaction. Compare the requirements for these two types of nuclear reactions. (3 marks)

 

(i)         An equation for the fission of uranium-235 is:

92U235 + 0n1           92U236               57La148 + 35Br85 + 3 0n1

 

If the masses of the atoms in this equation are:

92U235 = 235.044 a.m.u.

57La148 = 147.915 a.m.u.

35Br85 = 84.911 a.m.u.

0n1 = 1.009 a.m.u.

1 a.m.u. = 1.66 x 10-27 kg

 

(I) Calculate the mass defect in a.m.u. for the fission of 1 atom of uranium (1 mark)

(II) Calculate the energy released in joules from the fission of 1 atom of uranium.              (2 marks)

 

(j)         In 1934 Enrico Fermi irradiated uranium with neutrons. The product emitted beta particles and Fermi thought it was an isotope of uranium. Later work however showed that the product was consistent with being composed of smaller nuclei such as barium and lanthanum.

What was the name of the type of nuclear reaction that Fermi produced? (1 mark)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

….

 

 

 

 

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