AQA A Level Physics Paper 2 June 2018 question paper 7408/2

Explain what is meant by specific latent heat of fusion.

Figure 1 shows how the temperature of the water is maintained in a hot tub.

The hot tub system has a volume of 4.5 m³ and is filled with water at a temperature of 28 °C

The heater transfers thermal energy to the water at a rate of 2.7 kW while a pump circulates the water.

Assume that no heat is transferred to the surroundings.

Calculate the rise in water temperature that the heater could produce in 1.0 hour.

density of water = 1000 kg m^–3 specific heat capacity of water = 4200 J kg^–1 K^–1

The pump can circulate the water at different speeds. When working at higher speeds the rise in temperature is greater.

Explain why. Again assume that no heat is transferred to the surroundings.

Define the electric field strength at a point in an electric field.

Figure 2 shows a point charge of +46 C placed 120 mm from a point charge Q.

Position P is on the line joining the charges at a distance 66 mm from charge Q. The resultant electric field strength at position P is zero.

Calculate the charge Q.

Explain, without calculation, whether net work must be done in moving a proton from infinity to position P in Figure 2.

A small rubber ball coated with a conducting paint carries a positive charge. The ball is suspended in equilibrium from a vertical wall by an uncharged non-conducting thread of negligible mass. The wall is positively charged and produces a horizontal uniform electric field perpendicular to the wall along the whole of its length. Figure 3 shows that the thread makes an angle of 30° to the wall.

The thread breaks.

Explain the motion of the ball.

State what is meant by a capacitance of 370 F

The charging of a 370 F capacitor is investigated using the circuit shown in Figure 4 Both meters in the circuit are ideal.

The power supply of emf 9.8 V has a negligible internal resistance. The capacitor is initially uncharged. When the switch is closed at time t = 0 charge begins to flow through resistor R. The time constant of the charging circuit is 1.0 s

Calculate the resistance of R.

Identify, with the symbol X on Figure 5, the potential difference (pd) across the capacitor when the switch has been closed for 2.0 s Sketch the graph that shows how the pd varies from t = 0 to t = 2.0 s

Calculate the time taken for the charging current to fall to half its initial value.

Calculate the time taken for the charge on the capacitor to reach 3.0 mC

State Lenz’s law.

Lenz’s law can be demonstrated using a bar magnet and a coil of wire connected to a sensitive ammeter as shown in Figure 6.

The bar magnet is moved towards the coil and is then brought to a halt.

State how the reading on the ammeter changes during this process.

During the demonstration an induced current is detected by the ammeter. The induced current is in the direction E to F.

Explain how this demonstrates Lenz’s law.

Figure 7 shows an arrangement for investigating induced emf.

As shown, the uniform vertical magnetic field is confined to the gap between the poles of the magnet. The plane of the square coil is horizontal and is made of conducting wire. The coil consists of a single turn and is attached by flexible wire to an oscilloscope.

The oscilloscope gives a reading of 2.9 10^–4 V when the coil is moved at uniform speed from position G outside the field to position H inside the field, as shown in Figure 8.

Length of side of square coil = 32 mm

Magnetic flux density of uniform magnetic field = 0.38 T

Calculate the time taken to move the coil from position G to position H.

The square coil is rotated through 360 at a constant angular speed about the horizontal axis shown in Figure 9.

Calculate the angular speed of the coil when the maximum reading on the oscilloscope is 5.1 mV

Suggest, with a reason, which type of radiation is likely to be the most appropriate for the sterilisation of metallic surgical instruments.

Explain why the public need not worry that irradiated surgical instruments become radioactive once sterilised.

A student detects the counts from a radioactive source using a G-M radiation detector as shown in Figure 10.

The student measures the count rate for three different distances d. Table 1 shows the count rate, in counts per minute, corrected for background for each of these distances.

Explain, with the aid of suitable calculations, why the data in Table 1 are not consistent with an inverse-square law. You may use the blank columns for your working.

State two possible reasons why the results do not follow the expected inverse-square law.

Figure 11 shows how radioactive decay of one nuclide can be modelled by draining water through a tap from a cylindrical tube.

The water flow-rate is proportional to the pressure of the water. The pressure of the water is proportional to the depth of the water. Therefore the rate at which the depth decreases is proportional to the depth of the water.

Before the tap is opened the depth is 16.0 cm

The tap is opened and the depth is measured at regular intervals. These data are plotted on the graph in Figure 12.

Determine the predicted depth of water when the time is 57 s

Suggest how the apparatus in Figure 11 may be changed to represent a radioactive sample of the same nuclide with a greater number of nuclei.

Suggest how the apparatus in Figure 11 may be changed to represent a radioactive sample of a nuclide with a smaller decay constant.

The age of the Moon has been estimated from rock samples containing rubidium (Rb and strontium (Sr), brought back from Moon landings. ⁸⁷₃₇Rb decays to⁸⁷₃₈Sr with a radioactive decay constant of 1.42 10^–11 year^–1

Calculate, in years, the half-life of⁸⁷₃₇Rb.

A sample of Moon rock contains 1.23 mg of⁸⁷₃₇Rb.

Calculate the mass, in g, of⁸⁷₃₇Rb that the rock sample contained when it was formed 4.47 10⁹ years ago.

Give your answer to an appropriate number of significant figures.

Calculate the activity of a sample of⁸⁷₃₇Rb of mass 1.23 mg

Give an appropriate unit for your answer.

A nucleus of polonium Po may decay to the stable isotope of lead²⁰⁸₈₂Pb through a chain of emissions following the sequence ^{– –} .

Figure 13 shows the position of the isotope²⁰⁸₈₂Pb on a grid of neutron number N against proton number Z.

Draw four arrows on Figure 13 to show the sequence of changes to N and Z that occur as the polonium nucleus is transformed into²⁰⁸₈₂Pb.

A nucleus of the stable isotope²⁰⁸₈₂Pb has more neutrons than protons.

Explain why there is this imbalance between proton and neutron numbers by referring to the forces that operate within the nucleus. Your explanation should include the range of the forces and which particles are affected by the forces.

Many, but not all, isotopes of lead are stable. For example,²⁰⁵₈₂Pb decays by electron capture to become an isotope of thallium, Tl.

Write the equation to represent this decay, including the isotope of thallium produced.

The thallium nucleus is formed in an excited state. Electromagnetic radiation is emitted from the thallium atom following its formation.

Explain the origin and location of two sources of this radiation.

Other nuclides also emit electromagnetic radiation.

Explain why the metastable form of the isotope of technetium⁹⁹₄₃Tc is a radioactive source suitable for use in medical diagnosis.

Section B

Each of Questions 08 to 32 is followed by four responses, A, B, C and D.

For each question select the best response.

ideal gas at constant volume.

What is the gradient of the graph?

Two flasks X and Y are filled with an ideal gas and are connected by a tube of negligible volume compared to that of the flasks. The volume of X is twice the volume of Y. X is held at a temperature of 150 K and Y is held at a temperature of 300 K

The average mass of an air molecule is 4.8 × 10^–26 kg

What is the mean square speed of an air molecule at 750 K ?

A transparent illuminated box contains small smoke particles and air. The smoke particles are observed to move randomly when viewed through a microscope.

What is the cause of this observation of Brownian motion?

The diagram shows a gas particle about to collide elastically with a wall.

Which diagram shows the correct change in momentum mv that occurs during the collision?

The distance between the Sun and the Earth is 1.5 × 10¹¹ m

What is the gravitational force exerted on the Sun by the Earth?

The graph shows how the gravitational potential varies with distance between two planets, K and L, that have the same radius.

Which statement is correct?

The diagram shows equipotential lines near a group of asteroids.

Which arrow shows the direction of the gravitational field at X ?

Planet N has a gravitational potential V at its surface. Planet M has double the density and double the radius of planet N. Both planets are spherical and have uniform density.

What is the gravitational potential at the surface of planet M ?

A spacecraft of mass 1.0 × 10⁶ kg is in orbit around the Sun at a radius of 1.1 × 10¹¹ m The spacecraft moves into a new orbit of radius 2.5 × 10¹¹ m around the Sun.

What is the total change in gravitational potential energy of the spacecraft?

Which graph shows the relationship between the time period T and the orbital radius r of a planet in orbit around the Sun?

The Earth can be assumed to be a uniform sphere of radius R.

What is the mean density of the Earth?

A conducting sphere holding a charge of +10 C is placed centrally inside a second uncharged conducting sphere.

Which diagram shows the electric field lines for the system?

A charged spherical conductor has a radius r. An electric field of strength E exists at the surface due to the charge.

What is the potential of the spherical conductor?

Four positive charges are fixed at the corners of a square as shown.

The total potential at the centre of the square, a distance d from each charge, is .

What is the magnitude of the fourth charge?

An air-filled parallel-plate capacitor is charged from a source of emf. The electric field has a strength E between the plates. The capacitor is disconnected from the source of emf and the separation between the isolated plates is doubled.

What is the final electric field between the plates?

A parallel-plate capacitor has square plates of length l separated by distance d and is filled with a dielectric.

A second capacitor has square plates of length 2 l separated by distance 2 d and has air as its dielectric.

Both capacitors have the same capacitance.

What is the relative permittivity of the dielectric in the first capacitor?

The graph shows the variation of potential difference (pd) with charge for a capacitor while it is charging.

Which statement can be deduced from the graph?

Different magnetic fields are present in the two chambers shown. A particle enters the first chamber at a velocity of 80 m s^–1 and is deflected into a circular path of radius 200 mm In the second chamber it follows a circular path of radius 100 mm

The particle leaves the second chamber at a speed of

The diagram shows a clockwise current I in a circular coil placed in a uniform magnetic field B with the plane of the coil perpendicular to the magnetic field.

What is the effect on the coil of the interaction between the current and the magnetic field?

A transformer has an efficiency of 80% It has 7000 turns on its primary coil and 175 turns on its secondary coil. When the primary of the transformer is connected to a 240 V ac supply, the secondary current is 8.0 A

What are the primary current and secondary voltage?

nucleus?

The radius of a uranium²³⁸₉₂U nucleus is 7.75 × 10¹⁵ m What is the radius of a¹²₆C nucleus?

During a single fission event of uranium-235 in a nuclear reactor the total mass lost is 0.23 u. The reactor is 25% efficient.

How many events per second are required to generate 900 MW of power?

Which of the following substances can be used as a moderator in a nuclear reactor?