9702_s15_qp_43
A paper of Physics, 9702
Questions:
13
Year:
2015
Paper:
4
Variant:
3
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1
State Newton’s law of gravitation. The planet Neptune has eight moons . Each moon orbits Neptune in a circular path of radius r with a period T. Assuming that Neptune and each moon behave as point masses, show that r and T are related by the expression GMN = 4π2r3 T 2 where G is the gravitational constant and MN is the mass of Neptune. Data for the moon Triton that orbits Neptune and for the moon Oberon that orbits the planet Uranus are given in . planet moon radius of orbit r /105 km period of orbit T / days Neptune Uranus Triton Oberon 3.55 5.83 5.9 13.5
13. Gravitational fields  →  13.2. Gravitational force between point masses
13. Gravitational fields  →  13.3. Gravitational field of a point mass
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2
State what is meant by internal energy. The variation with volume V of the pressure p of an ideal gas as it undergoes a cycle ABCA of changes is shown in . 1.0 1.5 3.0 4.0 5.0 6.0 7.0 8.0 2.0 2.5 3.0 p / 105 Pa V / 10ï m3 3.5 4.0 A C B The temperature of the gas at A is 290 K. The temperature at B is 870 K. Determine the amount, in mol, of gas, amount = mol the temperature of the gas at C. temperature = K Explain why the change from C to A involves external work and a change in internal energy.
16. Thermodynamics  →  16.2. The first law of thermodynamics
15. Ideal gases  →  15.2. Equation of state
16. Thermodynamics  →  16.1. Internal energy
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3
Define specific latent heat. An electrical heater is immersed in some melting ice that is contained in a funnel, as shown in . heater melting ice water The heater is switched on and, when the ice is melting at a constant rate, the mass m of ice melted in 5.0 minutes is noted, together with the power P of the heater. The power P of the heater is then increased. A new reading for the mass m of ice melted in 5.0 minutes is recorded when the ice is melting at a constant rate. Data for the power P and the mass m are shown in . power of heater P / W mass m melted in 5.0 minutes / g mass m melted per second / g s−1 Complete to determine the mass melted per second for each power of the heater. Use the data in the completed to determine 1. a value for the specific latent heat of fusion L of ice, L = J g−1 2. the rate h of thermal energy gained by the ice from the surroundings. h = W
14. Temperature  →  14.3. Specific heat capacity and specific latent heat
16. Thermodynamics  →  16.2. The first law of thermodynamics
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5
A charged metal sphere is isolated in space. Measurements of the electric potential V are made for different distances x from the centre of the sphere. The variation with distance x of the potential V is shown in . 1.0 2.0 4.0 6.0 8.0 10.0 2.0 3.0 4.0 V / 103 V x / cm Use to determine the electric field strength, in N C−1, at a point where x = 4.0 cm. Explain your working. electric field strength = N C−1 The charge on the sphere is 8.0 × 10−9 C. Use to state the electric potential at the surface of the sphere. potential = V The sphere acts as a capacitor. Determine the capacitance of the sphere. capacitance = F
18. Electric fields  →  18.5. Electric potential
18. Electric fields  →  18.3. Electric force between point charges
18. Electric fields  →  18.4. Electric field of a point charge
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6
State the type of field, or fields, that may cause a force to be exerted on a particle that is uncharged and moving, charged and stationary, charged and moving at right-angles to the field. A particle X has mass 3.32 × 10−26 kg and charge +1.60 × 10−19 C. The particle is travelling in a vacuum with speed 7.60 × 104 m s−1. It enters a region of uniform magnetic field that is normal to the direction of travel of the particle. The particle travels in a semicircle of diameter 12.2 cm, as shown in . 12.2 cm path of particle X region of uniform magnetic field For the uniform magnetic field, state its direction, calculate the magnetic flux density. magnetic flux density = T A second particle Y has mass less than that of particle X in and the same charge. It enters the region of uniform magnetic field in with the same speed and along the same initial path as particle X. On , draw the path of particle Y in the region of the magnetic field.
20. Magnetic fields  →  20.3. Force on a moving charge
18. Electric fields  →  18.2. Uniform electric fields
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8
A photon of wavelength 6.50 × 10−12 m is incident on an isolated stationary electron, as illustrated in . incident photon electron mass me deflected photon wavelength 6.84 × 10–12 m e wavelength 6.50 × 10–12 m The photon is deflected elastically by the electron of mass me. The wavelength of the deflected photon is 6.84 × 10−12 m. Calculate, for the incident photon, its momentum, momentum = N s its energy. energy = J The angle θ through which the photon is deflected is given by the expression Δλ = h mec (1 – cos θ) where Δλ is the change in wavelength of the photon, h is the Planck constant and c is the speed of light in free space. Calculate the angle θ. θ = ° Use energy considerations to suggest why Δλ must always be positive.
22. Quantum physics  →  22.1. Energy and momentum of a photon
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9
An isotope of an element is radioactive. Explain what is meant by radioactive decay. At time t, a sample of a radioactive isotope contains N nuclei. In a short time Δt, the number of nuclei that decay is ΔN. State expressions, in terms of the symbols t, Δt, N and ΔN for the number of undecayed nuclei at time (t + Δt), number = the mean activity of the sample during the time interval Δt, mean activity = the probability of decay of a nucleus during the time interval Δt, probability = the decay constant. decay constant = The variation with time t of the activity A of a sample of a radioactive isotope is shown in . A t ½ 2t ½ 3t ½ t The radioactive isotope decays to form a stable isotope S. At time t = 0, there are no nuclei of S in the sample. On the axes of , sketch a graph to show the variation with time t of the number n of nuclei of S in the sample. n t ½ 2t ½ 3t ½ t
23. Nuclear physics  →  23.2. Radioactive decay
11. Particle physics  →  11.1. Atoms, nuclei and radiation
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10
An operational amplifier (op-amp) is used in the comparator circuit of . V IN V OUT 1.2 k1 4.2 k1 R –5 V +5 V +4.5 V + – Show that the potential at the inverting input of the op-amp is +1.0 V. Explain why the potential difference across resistor R is + 5 V when VIN is greater than 1.0 V and is zero when VIN is less than 1.0 V. VIN > 1.0 V: VIN The variation with time t of the input voltage VIN is shown in . 0 0 time t V IN +1 V voltage / V On the axes of , draw the variation with time t of the output potential VOUT. Suggest a use for this type of circuit.
10. D.C. circuits  →  10.3. Potential dividers
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11
State and explain how, in an X-ray tube, the hardness of the X-ray beam is controlled. A parallel beam of X-rays has intensity I0 and is incident on a medium having a linear absorption coefficient μ. State an equation for the variation of the intensity I with the thickness x of the medium. Data for the linear absorption coefficient μ for an X-ray beam in blood and in muscle is shown in . μ / cm−1 blood muscle 0.23 0.22 Suggest why, if this X-ray beam is used to image blood vessels in muscle, contrast on the image would be poor.
24. Medical physics  →  24.2. Production and use of X-rays
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12
Information may be carried by means of various channels of communication. Name examples, one in each case, of devices where information is carried to the device using a wire pair, a coaxial cable, microwaves. State two advantages of optic fibres as compared with coaxial cables for long-range communication. 1. 2. An optic fibre has length 62 km and an attenuation per unit length of 0.21 dB km−1. The input power to the fibre is P. At the receiver, the noise power is 9.2 μW. The signal-to-noise ratio at the receiver is 25 dB. Calculate the ratio, in dB, of the input power P to the noise power at the receiver. ratio = dB Use your answer in to determine the input power P . P = W
8. Superposition  →  8.3. Interference
7. Waves  →  7.5. Polarisation
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13
During magnetic resonance imaging to obtain information about internal body structures, a large constant magnetic field is used with a calibrated non-uniform magnetic field superimposed on it. State and explain the purpose of the large constant magnetic field, the non-uniform magnetic field. The de-excitation energy E (measured in joule) of a proton in magnetic resonance imaging is given by the expression E = 2.82 × 10−26 B where B is the magnetic flux density measured in tesla. The energy E is emitted as a photon of electromagnetic radiation in the radio-frequency range. Calculate the magnetic flux density required for the radio frequency to be 42 MHz. magnetic flux density = T
20. Magnetic fields  →  20.5. Electromagnetic induction
20. Magnetic fields  →  20.1. Concept of a magnetic field
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