9702_w10_qp_41
A paper of Physics, 9702
Questions:
12
Year:
2010
Paper:
4
Variant:
1
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1
Define gravitational field strength. An isolated star has radius R. The mass of the star may be considered to be a point mass at the centre of the star. The gravitational field strength at the surface of the star is gs. On , sketch a graph to show the variation of the gravitational field strength of the star with distance from its centre. You should consider distances in the range R to 4R. 0R 2R 3R 4R distance 0.2gs 0.4gs 0.6gs 0.8gs gravitational field strength surface of star 1.0gs The Earth and the Moon may be considered to be spheres that are isolated in space with their masses concentrated at their centres. The masses of the Earth and the Moon are 6.00 × 1024 kg and 7.40 × 1022 kg respectively. The radius of the Earth is RE and the separation of the centres of the Earth and the Moon is 60 RE, as illustrated in . Earth mass 6.00 x 1024 kg Moon mass 7.40 x 1022 kg RE 60 RE (not to scale) For Examiner’s Use Explain why there is a point between the Earth and the Moon at which the gravitational field strength is zero. Determine the distance, in terms of RE, from the centre of the Earth at which the gravitational field strength is zero. distance = RE On the axes of , sketch a graph to show the variation of the gravitational field strength with position between the surface of the Earth and the surface of the Moon. gravitational field strength surface of Earth surface of Moon distance
13. Gravitational fields  →  13.4. Gravitational potential
13. Gravitational fields  →  13.3. Gravitational field of a point mass
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2
For Examiner’s Use State the basic assumption of the kinetic theory of gases that leads to the conclusion that the potential energy between the atoms of an ideal gas is zero. State what is meant by the internal energy of a substance. Explain why an increase in internal energy of an ideal gas is directly related to a rise in temperature of the gas. A fixed mass of an ideal gas undergoes a cycle PQRP of changes as shown in . volume / 10–4 m3 pressure / 105 Pa Q P R For Examiner’s Use State the change in internal energy of the gas during one complete cycle PQRP. change = J Calculate the work done on the gas during the change from P to Q. work done = J Some energy changes during the cycle PQRP are shown in . change work done on gas / J heating supplied to gas / J increase in internal energy / J P Q Q R R P –600 +720 +480 Complete to show all of the energy changes.
16. Thermodynamics  →  16.2. The first law of thermodynamics
16. Thermodynamics  →  16.1. Internal energy
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3
For Examiner’s Use A student sets up the apparatus illustrated in in order to investigate the oscillations of a metal cube suspended on a spring. variable-frequency oscillator thread pulley spring metal cube The amplitude of the vibrations produced by the oscillator is constant. The variation with frequency of the amplitude of the oscillations of the metal cube is shown in . amplitude / mm frequency / Hz State the phenomenon illustrated in . For the maximum amplitude of vibration, state the magnitudes of the amplitude and the frequency. amplitude = mm frequency = Hz For Examiner’s Use The oscillations of the metal cube of mass 150 g may be assumed to be simple harmonic. Use your answers in to determine, for the metal cube, its maximum acceleration, acceleration = m s–2 the maximum resultant force on the cube. force = N Some very light feathers are attached to the top surface of the cube so that the feathers extend outwards, beyond the vertical sides of the cube. The investigation is now repeated. On , draw a line to show the new variation with frequency of the amplitude of vibration for frequencies between 2 Hz and 10 Hz.
17. Oscillations  →  17.1. Simple harmonic oscillations
17. Oscillations  →  17.3. Damped and forced oscillations, resonance
6. Deformation of solids  →  6.1. Stress and strain
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4
For Examiner’s Use Define capacitance. An isolated metal sphere has a radius r. When charged to a potential V, the charge on the sphere is q. The charge may be considered to act as a point charge at the centre of the sphere. State an expression, in terms of r and q, for the potential V of the sphere. This isolated sphere has capacitance. Use your answers in and to show that the capacitance of the sphere is proportional to its radius. The sphere in has a capacitance of 6.8 pF and is charged to a potential of 220 V. Calculate the radius of the sphere, radius = m For Examiner’s Use the charge, in coulomb, on the sphere. charge = C A second uncharged metal sphere is brought up to the sphere in so that they touch. The combined capacitance of the two spheres is 18 pF. Calculate the potential of the two spheres, potential = V the change in the total energy stored on the spheres when they touch. change = J
19. Capacitance  →  19.1. Capacitors and capacitance
18. Electric fields  →  18.3. Electric force between point charges
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5
For Examiner’s Use Positive ions are travelling through a vacuum in a narrow beam. The ions enter a region of uniform magnetic field of flux density B and are deflected in a semi-circular arc, as shown in . 12.8 cm detector beam of positive ions uniform magnetic field The ions, travelling with speed 1.40 × 105 m s–1, are detected at a fixed detector when the diameter of the arc in the magnetic field is 12.8 cm. By reference to , state the direction of the magnetic field. The ions have mass 20 u and charge +1.6 × 10–19 C. Show that the magnetic flux density is 0.454 T. Explain your working. For Examiner’s Use Ions of mass 22 u with the same charge and speed as those in are also present in the beam. On , sketch the path of these ions in the magnetic field of magnetic flux density 0.454 T. In order to detect these ions at the fixed detector, the magnetic flux density is changed. Calculate this new magnetic flux density. magnetic flux density = T
20. Magnetic fields  →  20.3. Force on a moving charge
20. Magnetic fields  →  20.5. Electromagnetic induction
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6
For Examiner’s Use A simple iron-cored transformer is illustrated in . output input primary coil secondary coil iron core State why the primary and secondary coils are wound on a core made of iron. Suggest why thermal energy is generated in the core when the transformer is in use. For Examiner’s Use The root-mean-square (r.m.s.) voltage and current in the primary coil are VP and IP respectively. The r.m.s. voltage and current in the secondary coil are VS and IS respectively. Explain, by reference to direct current, what is meant by the root-mean-square value of an alternating current. Show that, for an ideal transformer, VS VP = IP IS .
21. Alternating currents  →  21.1. Characteristics of alternating currents
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7
For Examiner’s Use State an effect, one in each case, that provides evidence for the wave nature of a particle, the particulate nature of electromagnetic radiation. Four electron energy levels in an atom are shown in . electron energy –0.87 × 10–19 J –1.36 × 10–19 J –2.42 × 10–19 J –5.44 × 10–19 J (not to scale) An emission spectrum is associated with the electron transitions between these energy levels. For this spectrum, state the number of lines, calculate the minimum wavelength. wavelength = m
22. Quantum physics  →  22.4. Energy levels in atoms and line spectra
22. Quantum physics  →  22.3. Wave-particle duality
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8
For Examiner’s Use In some power stations, nuclear fission is used as a source of energy. State what is meant by nuclear fission. The nuclear fission reaction produces neutrons. In the power station, the neutrons may be absorbed by rods made of boron-10. Complete the nuclear equation for the absorption of a single neutron by a boron-10 nucleus with the emission of an a-particle. 5B + 3Li + Suggest why, when neutrons are absorbed in the boron rods, the rods become hot as a result of this nuclear reaction.
23. Nuclear physics  →  23.1. Mass defect and nuclear binding energy
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9
An amplifier circuit incorporating an operational amplifier (op-amp) is shown in . R2 VIN VOUT R1 – –9 V +9 V + State the name of this type of amplifier circuit, the gain G in terms of resistances R1 and R2. For Examiner’s Use The value of R1 is 820 Ω. The resistor of resistance R2 is replaced with a light-dependent resistor (LDR). The input potential difference VIN is 15 mV. Calculate the output potential difference VOUT for the LDR having a resistance of 100 Ω (the LDR is in sunlight), VOUT = V 1.0 MΩ (the LDR is in darkness). VOUT = V
10. D.C. circuits  →  10.3. Potential dividers
9. Electricity  →  9.3. Resistance and resistivity
10. D.C. circuits  →  10.1. Practical circuits
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10
For Examiner’s Use 10 State what is meant by the acoustic impedance of a medium. Data for some media are given in . medium speed of ultrasound / m s–1 acoustic impedance / kg m–2 s–1 air gel soft tissue bone 4.3 × 102 1.5 × 106 1.6 × 106 7.0 × 106 Use data from to calculate a value for the density of bone. density = kg m–3 A parallel beam of ultrasound has intensity I. It is incident at right-angles to a boundary between two media, as shown in . transmitted intensity IT reflected intensity IR incident intensity I acoustic impedance Z2 acoustic impedance Z1 boundary The media have acoustic impedances of Z1 and Z2. The transmitted intensity of the ultrasound beam is IT and the reflected intensity is IR. State the relation between I, IT and IR. For Examiner’s Use The reflection coefficient a is given by the expression a = (Z2 – Z1)2 (Z2 + Z1)2. Use data from to determine the reflection coefficient a for a boundary between 1. gel and soft tissue, a = 2. air and soft tissue. a = By reference to your answers in , explain the use of a gel on the surface of skin during ultrasound diagnosis.
24. Medical physics  →  24.1. Production and use of ultrasound
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11
For Examiner’s Use 11 Wire pairs provide one means of communication but they are subject to high levels of noise and attenuation. Explain what is meant by noise, attenuation. A microphone is connected to a receiver using a wire pair, as shown in . receiver wire pair microphone The wire pair has an attenuation per unit length of 12 dB km–1. The noise power in the wire pair is 3.4 × 10–9 W. The microphone produces a signal power of 2.9 lW. Calculate the maximum length of the wire pair so that the minimum signal-to-noise ratio is 24 dB. length = m Communication over distances greater than that calculated in is required. Suggest how the circuit of may be modified so that the minimum signal-to-noise ratio at the receiver is not reduced.
24. Medical physics  →  24.1. Production and use of ultrasound
6. Deformation of solids  →  6.1. Stress and strain
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