OCR A Level Physics A Unified Physics November 2020 question paper H556/03

A ball coated with conducting paint has weight 0.030 N and radius 1.0 cm. The ball is suspended from an insulating thread. The distance between the pivot and the centre of the ball is 120 cm.

The ball is placed between two vertical metal plates. The separation between the plates is 8.0 cm. The plates are connected to a 4.0 kV power supply.

Show that the electric force acting on the charged ball is 4.5 × 10^–4 N.

Draw, on the diagram above, arrows which represent the three forces acting on the ball.

Label each arrow with the name of the force it represents.

By taking moments about the pivot, or otherwise, show that x = 1.8 cm.

The diagram below shows a circuit containing two capacitors which are both initially uncharged. The battery has e.m.f. E and negligible internal resistance.

The switch S is first moved to position A until the capacitor of capacitance C₀ is fully charged.

The switch S is then moved to position B. The initial charge stored by the capacitor of capacitance C₀ is shared between the two capacitors. The final reading on the voltmeter is V.

A student wants to determine the values of E and C₀ by repeating the experiment above and measuring the potential difference (p.d.) V for a selection of capacitors of capacitance C. The student decides to plot a graph of against C.

The data points, error bars and the line of best fit drawn by the student are shown in the graph below.

The gradient of the line of best fit is 51 V^–1 F^–1. The value of E is 9.1 V.

Determine the value of C₀ in millifarads (mF). Write your answer to 2 significant figures.

Draw on the graph a straight line of worst fit.

Use this line to determine the absolute uncertainty in your value of C₀. Write your answer to an appropriate number of significant figures.

This question is about the Sun and its radiation.

Use the data below to show that the luminosity of the Sun is about 4 × 10²⁶ W. (a) (i)

• radius of Sun = 7.0 × 10⁸ m

• surface temperature of Sun = 5800 K

Sirius, the brightest star in the night sky, has a luminosity 25 times greater than that of the Sun. It has diameter 1.7 times greater than that of the Sun.

Calculate the surface temperature T of Sirius.

Both the ISS and the astronauts inside it are in free fall.

Explain why this makes the astronauts feel weightless.

Calculate the value of the gravitational field strength g at the height of the ISS above the Earth.

=........ N kg^–1 g

Use the information in (b)(ii) and the data below to show that the root mean square (r.m.s.) speed of the air molecules inside the ISS is approximately 15 times smaller than the orbital speed of the ISS.

• molar mass of air = 2.9 × 10^–2 kg mol^–1

• temperature of air inside the ISS = 20 °C

The ISS has arrays of solar cells on its wings. These solar cells charge batteries which power the ISS. The wings always face the Sun.

Use the data below and your answer to (b)(ii) to calculate the average power delivered to the batteries.

• The total area of the cells facing the solar radiation is 2500 m².

• 7% of the energy of the sunlight incident on the cells is stored in the batteries.

• The intensity of solar radiation at the orbit of the ISS is 1.4 kW m^–2 outside of the Earth’s shadow and zero inside it.

• The ISS passes through the Earth’s shadow for 35 minutes during each orbit.

Calculate the frequency f of the transmitted wave.

The electromagnetic wave is caused by electrons oscillating in the transmitter aerial. Each electron oscillates with simple harmonic motion.

Calculate the maximum acceleration a_max of an electron which oscillates with an amplitude of 4.0 × 10^–6 m.

=........ m s^–2 a_max

Suggest why the diode in Fig. 5.1 is necessary for an ammeter to detect a signal at the receiver aerial.

A beam of -particles is incident on a thin gold foil. Most -particles pass straight through the foil. A few are deflected by gold nuclei.

The diagram shows the path of one -particle which passes close to a gold nucleus N in the foil. The -particle is deflected through an angle of 60° as it travels from A to B.

P marks its position of closest approach to the gold nucleus.

Another -particle in the beam is deflected by the same gold nucleus N through an angle of 30°.

Sketch its path onto the diagram above.

The initial kinetic energy of each -particle is 5.0 MeV.

Show that the magnitude of the initial momentum of each -particle is about 10^–19 kg m s^–1 Take the mass of the -particle to be 6.6 × 10^–27 kg.

Draw two vectors in the spaces below to represent the initial momentum and the final momentum of the -particle.

initial momentum at A

final momentum at B

Draw a vector in the space below to represent the momentum of the nucleus N when the -particle reaches B.

Explain how you determined this momentum.