9702_w18_qp_41
A paper of Physics, 9702
Questions:
12
Year:
2018
Paper:
4
Variant:
1
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1
State what is meant by gravitational potential at a point. Suggest why, for small changes in height near the Earth’s surface, gravitational potential is approximately constant. The Moon may be considered to be a uniform sphere with a diameter of 3.5 × 103 km and a mass of 7.4 × 1022 kg. A meteor strikes the Moon and, during the collision, a rock is sent off from the surface of the Moon with an initial speed v. Assuming that the Moon is isolated in space, determine the minimum speed of the rock such that it does not return to the Moon’s surface. Explain your working. minimum speed = m s–1
13. Gravitational fields  →  13.4. Gravitational potential
13. Gravitational fields  →  13.3. Gravitational field of a point mass
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2
State what is meant by the internal energy of a system. An ideal gas undergoes a cycle of changes as shown in . 3.00 2.80 2.60 2.40 2.20 2.00 pressure / 105 Pa volume / cm3 P R Q 97.0 J 280 K 332 K 372 K At point P, the gas has volume 950 cm3, pressure 2.10 × 105 Pa and temperature 280 K. The gas is heated at constant volume and 97.0 J of thermal energy is transferred to the gas. Its pressure and temperature change so that the gas is at point Q on . The gas then undergoes the change from point Q to point R and then from point R back to point P, as shown on . Some energy changes that take place during the cycle PQRP are shown in . change P → Q change Q → R change R → P thermal energy transferred to gas / J work done on gas / J increase in internal energy of gas / J +97.0 –42.5 +37.0 State the total change in internal energy of the gas during the complete cycle PQRP. Explain your answer. On , complete the energy changes for the gas during 1. the change P → Q, 2. the change Q → R, 3. the change R → P.
16. Thermodynamics  →  16.2. The first law of thermodynamics
16. Thermodynamics  →  16.1. Internal energy
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3
A U-tube contains liquid, as shown in . liquid liquid L x x The total length of the column of liquid in the tube is L. The column of liquid is displaced so that the change in height of the liquid in each arm of the U-tube is x, as shown in . The liquid in the U-tube then oscillates with simple harmonic motion such that the acceleration a of the column is given by the expression a = – L g e o x where g is the acceleration of free fall. Calculate the period T of oscillation of the liquid column for a column length L of 19.0 cm. T = s The variation with time t of the displacement x is shown in . +2.0 +1.0 T 2T 3T t x / cm –1.0 –2.0 The period of oscillation of the liquid column of mass 18.0 g is T. The oscillations are damped. Suggest one cause of the damping. Calculate the loss in total energy of the oscillations during the first 2.5 periods of the oscillations. energy loss = J
17. Oscillations  →  17.1. Simple harmonic oscillations
17. Oscillations  →  17.3. Damped and forced oscillations, resonance
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4
Explain the main principles behind the use of ultrasound to obtain diagnostic information about internal body structures. Define specific acoustic impedance. The fraction of the incident intensity of an ultrasound beam that is reflected at a boundary between two media depends on the specific acoustic impedances Z1 and Z2 of the media. Discuss qualitatively how the relative magnitudes of the two specific acoustic impedances affect the reflected intensity.
24. Medical physics  →  24.1. Production and use of ultrasound
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5
State two advantages of the transmission of data in digital form, compared with the transmission in analogue form. 1. . 2. The digital numbers shown in are transmitted at a sampling rate of 500 Hz. end of transmission start of transmission The digital numbers are received, after transmission, by a digital-to-analogue converter (DAC). On , complete the graph to show the variation with time t of the signal level from the DAC. t / ms signal level State the effect on the transmitted analogue signal when the sampling rate of the analogue-to-digital converter (ADC) and of the DAC is increased, the number of bits in each sample is increased.
21. Alternating currents  →  21.2. Rectification and smoothing
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6
Define electric potential at a point. State the relationship between electric potential and electric field strength at a point. Two parallel metal plates A and B are situated a distance 1.2 cm apart in a vacuum, as shown in . 1.2 cm –75 V plate B plate A helium nucleus x 0 V Plate A is earthed and plate B is at a potential of –75 V. A helium nucleus is situated between the plates, a distance x from plate A. Initially, the helium nucleus is at rest on plate A where x = 0. The helium nucleus is free to move between the plates. By considering energy changes of the helium nucleus, explain why the speed at which it reaches plate B is independent of the separation of the plates. As the helium nucleus (4 2He) moves from plate A towards plate B, its distance x from plate A increases. Calculate the speed of the nucleus after it has moved a distance x = 0.40 cm from plate A. speed = m s–1
18. Electric fields  →  18.5. Electric potential
18. Electric fields  →  18.2. Uniform electric fields
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7
An ideal operational amplifier (op-amp) has infinite bandwidth and infinite slew rate. State what is meant by infinite bandwidth, infinite slew rate. An incomplete circuit for a non-inverting amplifier incorporating an ideal operational amplifier is shown in . V OUT V IN + – R2 R1 +5.0 V –5.0 V On , draw lines to show the connections between the components to complete the circuit. The completed amplifier of has a voltage gain of 10. State the output voltage VOUT for an input voltage VIN of –0.36 V, VOUT = V 0.56 V. VOUT = V
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8
Explain what is meant by a magnetic field. A particle has mass m, charge +q and speed v. The particle enters a uniform magnetic field of flux density B such that, on entry, it is moving normal to the magnetic field, as shown in . path of particle mass m charge +q speed v region of magnetic field The direction of the magnetic field is perpendicular to, and into, the plane of the paper. On , draw the path of the particle through, and beyond, the region of the magnetic field. There is a force acting on the particle, causing it to accelerate. Explain why the speed of the particle on leaving the magnetic field is v. The particle in loses an electron so that its charge becomes +2q. Its change in mass is negligible. Determine, in terms of v, the initial speed of the particle such that its path through the magnetic field is unchanged. Explain your working. speed =
20. Magnetic fields  →  20.3. Force on a moving charge
20. Magnetic fields  →  20.1. Concept of a magnetic field
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9
State Faraday’s law of electromagnetic induction. A solenoid S is wound on a soft-iron core, as shown in . V V coil C soft-iron core Hall probe solenoid S A coil C having 120 turns of wire is wound on to one end of the core. The area of cross- section of coil C is 1.5 cm2. A Hall probe is close to the other end of the core. When there is a constant current in solenoid S, the flux density in the core is 0.19 T. The reading on the voltmeter connected to the Hall probe is 0.20 V. The current in solenoid S is now reversed in a time of 0.13 s at a constant rate. Calculate the reading on the voltmeter connected to coil C during the time that the current is changing. reading = V Complete for the voltmeter readings for the times before, during and after the direction of the current is reversed. before current changes during current change when current is zero after current changes reading on voltmeter connected to coil C / V reading on voltmeter connected to Hall probe / V 0.20
20. Magnetic fields  →  20.5. Electromagnetic induction
20. Magnetic fields  →  20.4. Magnetic fields due to currents
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12
State what is meant by radioactive decay. The variation with time t of the number N of undecayed nuclei in a sample of a radioactive isotope is shown in . 1.0 2.0 3.0 4.0 5.0 6.0 t / hours N / 1010 Use the gradient of the line in to determine the activity, in Bq, of the sample at time t = 4.0 hours. Show your working. activity = Bq Use your answer in to show that the decay constant λ of the isotope is approximately 4 × 10–5 s–1. A sample of a different radioactive isotope has an initial activity of 4.6 × 103 Bq. The sample must be stored safely until its activity is reduced to 1.0 × 103 Bq. The decay constant of the isotope is 5.5 × 10–7 s–1. The decay products are not radioactive. Calculate the minimum time, in days, for which the sample must be stored. time = days
23. Nuclear physics  →  23.2. Radioactive decay
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