9702_s21_qp_43
A paper of Physics, 9702
Questions:
12
Year:
2021
Paper:
4
Variant:
3
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1
The Earth may be assumed to be an isolated uniform sphere with its mass of 6.0 × 1024 kg concentrated at its centre. A satellite of mass 1200 kg is in a circular orbit about the Earth in the Earth’s gravitational field. The period of the orbit is 94 minutes. Define gravitational field strength. Calculate the radius of the orbit of the satellite. radius = m Rockets on the satellite are fired so that the satellite enters a different circular orbit that has a period of 150 minutes. The change in the mass of the satellite may be assumed to be negligible. Show that the radius of the new orbit is 9.4 × 106 m. State, with a reason, whether the gravitational potential energy of the satellite increases or decreases. Determine the magnitude of the change in the gravitational potential energy of the satellite. change in potential energy = J
5. Work, energy and power  →  5.2. Gravitational potential energy and kinetic energy
13. Gravitational fields  →  13.2. Gravitational force between point masses
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2
An ideal gas is contained in a cylinder by means of a movable frictionless piston, as illustrated in . cylinder gas molecule movement of piston piston Initially, the gas has a volume of 1.8 × 10−3 m3 at a pressure of 3.3 × 105 Pa and a temperature of 310 K. Show that the number of gas molecules in the cylinder is 1.4 × 1023. Use kinetic theory to explain why, when the piston is moved so that the gas expands, this causes a decrease in the temperature of the gas. The gas expands so that its volume increases to 2.4 × 10−3 m3 at a pressure of 2.3 × 105 Pa and a temperature of 288 K, as shown in . 1.8 × 10−3 m3 2.4 × 10−3 m3 3.3 × 105 Pa 2.3 × 105 Pa 310 K 288 K The average translational kinetic energy EK of a molecule of an ideal gas is given by EK = 3 2 kT where k is the Boltzmann constant and T is the thermodynamic temperature. Calculate the increase in internal energy ΔU of the gas during the expansion. ΔU = J The work done by the gas during the expansion is 76 J. Use your answer in to explain whether thermal energy is transferred to or from the gas during the expansion.
15. Ideal gases  →  15.3. Kinetic theory of gases
16. Thermodynamics  →  16.2. The first law of thermodynamics
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3
State what is meant by simple harmonic motion. A trolley of mass m is held on a horizontal surface by means of two springs. One spring is attached to a fixed point P. The other spring is connected to an oscillator, as shown in . P spring spring trolley oscillator The springs, each having spring constant k of 130 N m−1, are always extended. The oscillator is switched off. The trolley is displaced along the line of the springs and then released. The resulting oscillations of the trolley are simple harmonic. The acceleration a of the trolley is given by the expression a = − 2k m x where x is the displacement of the trolley from its equilibrium position. The mass of the trolley is 840 g. Calculate the frequency f of oscillation of the trolley. f = Hz ⎛ ⎞ ⎝ ⎠ The oscillator in is switched on. The frequency of oscillation of the oscillator is varied, keeping its amplitude of oscillation constant. The amplitude of oscillation of the trolley is seen to vary. The amplitude is a maximum at the frequency calculated in . State the name of the effect giving rise to this maximum. At any given frequency, the amplitude of oscillation of the trolley is constant. Explain how this indicates that there are resistive forces opposing the motion of the trolley.
17. Oscillations  →  17.1. Simple harmonic oscillations
6. Deformation of solids  →  6.1. Stress and strain
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5
State what is meant by the amplitude modulation (AM) of a radio wave. A radio wave is modulated by an audio signal. The variation with frequency f of the amplitude of the modulated wave is shown in . amplitude f / kHz Determine: the wavelength of the carrier wave wavelength = m the bandwidth of the modulated wave bandwidth = kHz the maximum frequency of the audio signal. maximum frequency = kHz The power of a radio signal at a transmitter is PT. At a receiver, the received power PR is given by the expression PR = 0.082 PT x2 where x is the distance, in metres, between the transmitter and the receiver. For the transmission of this signal, the attenuation is 73 dB. Determine the distance x. x = m
7. Waves  →  7.1. Progressive waves
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6
An isolated metal sphere of radius r is charged so that the electric field strength at its surface is E0. On , sketch the variation of the electric field strength E with distance x from the centre of the sphere. Your sketch should extend from x = 0 to x = 3r. r 2r 3r E0 field strength E distance x The de Broglie wavelength of a particle is λ 0 when its momentum is p0. On , sketch the variation with momentum p of the de Broglie wavelength λ of the particle for values of momentum from p0 2 to p0. p0 p0 momentum p wavelength λ λ λ A radioactive isotope decays with a half-life of 15 s to form a stable product. A fresh sample of the radioactive isotope at time t = 0 contains N0 nuclei and no nuclei of the stable product. On , sketch the variation with t of the number n of nuclei of the stable product for time t = 0 to time t = 45 s. time t / s number n 0.5 N0 N0
23. Nuclear physics  →  23.2. Radioactive decay
11. Particle physics  →  11.1. Atoms, nuclei and radiation
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7
State what is meant by the capacitance of a parallel plate capacitor. A capacitor of capacitance C is connected into the circuit shown in . A sensitive ammeter A V B C + – When the two-way switch is in position A, the capacitor is charged so that the potential difference across it is V. The switch moves to position B and the capacitor fully discharges through the sensitive ammeter. The switch moves repeatedly between A and B so that the capacitor charges and then discharges with frequency f. Show that the average current I in the ammeter is given by the expression I = fCV. For a potential difference V of 150 V and a frequency f of 60 Hz, the average current in the ammeter is 4.8 μA. Calculate the capacitance, in pF, of the capacitor. capacitance = pF A second capacitor, having the same capacitance as the capacitor in , is connected into the circuit of . The two capacitors are connected in series. State and explain the new reading on the ammeter. new reading = μA
19. Capacitance  →  19.1. Capacitors and capacitance
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8
The variation with temperature of the resistance of a thermistor is shown in . 1.0 2.0 3.0 4.0 resistance / kΩ temperature / °C A student includes the thermistor and an ideal operational amplifier (op-amp) in the circuit of . – + 3.0 kΩ 5.0 kΩ 2.5 kΩ +3.0 V + – Calculate the potential V + at the non-inverting input of the op-amp. V + = V At 10 °C, the resistance of the thermistor is 2.5 kΩ. State and explain whether the light-emitting diode (LED) is emitting light. Explain why the student’s circuit will not indicate any change in temperature above 0 °C. The resistor of resistance 5.0 kΩ is changed to a resistor of resistance R so that the LED switches on or off at a temperature of 20 °C. Determine R in kΩ. R = kΩ
9. Electricity  →  9.3. Resistance and resistivity
10. D.C. circuits  →  10.3. Potential dividers
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9
State what is meant by a magnetic field. A rectangular piece of aluminium foil is situated in a uniform magnetic field of flux density B, as shown in . aluminium foil magnetic field, flux density B Q R T P V W S movement of electrons The magnetic field is normal to the face PQRS of the foil. Electrons, each of charge −q, enter the foil at right angles to the face PQTV. On , shade the face of the foil on which electrons initially accumulate. Explain why electrons do not continuously accumulate on the face you have shaded. The Hall voltage VH developed across the foil in is given by the expression VH = BI ntq where I is the current in the foil. State the meaning of the quantity n. Using the letters on , identify the distance t. Suggest why, in practice, Hall probes are usually made using a semiconductor material rather than a metal.
20. Magnetic fields  →  20.3. Force on a moving charge
20. Magnetic fields  →  20.5. Electromagnetic induction
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10
State Lenz’s law. A metal ring is suspended from a fixed point P by means of a thread, as shown in . P metal ring P metal ring magnet pole piece N S The ring is displaced a distance d and then released. The ring completes many oscillations before coming to rest. The poles of a magnet are now placed near to the ring so that the ring hangs midway between the poles of the magnet, as shown in . The ring is again displaced a distance d and then released. Explain why the ring completes fewer oscillations before coming to rest. The ring in is now cut so that it has the shape shown in . Explain why, when the procedure in is repeated, the cut ring completes more oscillations than the complete ring when oscillating between the poles of the magnet.
20. Magnetic fields  →  20.5. Electromagnetic induction
6. Deformation of solids  →  6.1. Stress and strain
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11
State how, in a modern X-ray tube, the intensity of the X-ray beam and its hardness are controlled. intensity: hardness: A model of a limb consists of soft tissue and bone, as illustrated in . I0 I0 IC IS incident intensity transmitted intensity bone soft tissue 9.0 cm 3.0 cm The soft tissue has a thickness of 9.0 cm. The bone within the soft tissue has a thickness of 3.0 cm. Data for the linear attenuation coefficient μ of X-rays in soft tissue and in bone are shown in Table 11.1. Table 11.1 μ / cm−1 soft tissue 0.92 bone 2.90 A parallel beam of X-rays of intensity I0 is incident normally on the model. Calculate, in terms of I0: the transmitted intensity IS through soft tissue alone IS = I0 the transmitted intensity IC through soft tissue and bone. IC = I0 By reference to your answers in , suggest, with a reason, whether good contrast on an X-ray image would be obtained.
24. Medical physics  →  24.2. Production and use of X-rays
24. Medical physics  →  24.1. Production and use of ultrasound
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12
Electromagnetic radiation of a single constant frequency is incident on a metal surface. This causes an electron to be emitted. Explain why the maximum kinetic energy of the electron is independent of the intensity of the incident radiation. Ultraviolet radiation of wavelength 250 nm is incident on the surface of a sheet of zinc. The maximum kinetic energy of the emitted electrons is 1.4 eV. Determine, in eV: the energy of a photon of the ultraviolet radiation energy = eV the work function energy of the surface of the zinc. energy = eV
22. Quantum physics  →  22.2. Photoelectric effect
22. Quantum physics  →  22.1. Energy and momentum of a photon
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