OCR A Level Physics A Unified Physics June 2023 question paper H556/03

The MAVEN spacecraft orbits Mars and studies its upper atmosphere.

The diagram below shows the orbit of MAVEN around Mars.

Mark an X on the diagram to show the point in the orbit where MAVEN has maximum

acceleration.

Explain how Kepler’s 1st law applies to MAVEN’s orbit around Mars.

The table shows data for four orbits around Mars.

Phobos and Deimos are moons of Mars.

An areostationary orbit for Mars is the equivalent of a geostationary orbit for Earth.

Show that Kepler’s 3rd law applies to this data.

Suggest two reasons why MAVEN was not placed in an areostationary orbit.

A student uses the circuit below to investigate the resistivity of a wire.

The cell has e.m.f. and internal resistance r. The wire has resistivity and diameter d.

The student takes five measurements of the diameter of the wire, which are shown in the table below.

Suggest how the student made these measurements.

The student calculates the value of the diameter as d = 0.455 ± 0.005 mm.

Explain how the student calculated the value of the diameter, and its uncertainty, from the data in the table above.

The student varies the length L of the wire in the circuit and records the current I using the ammeter.

The student plots a graph of against L. The data points, error bars, line of best fit and a line of worst fit are shown in the graph below.

The cell has e.m.f. = 1.45 ± 0.05 V

The wire has diameter d = 0.455 ± 0.005 mm

1 Calculate the gradient of the best fit line and use this to determine a value for the resistivity of the wire.

You are not required to determine an uncertainty.

2 Determine a value for the internal resistance r of the cell and its absolute uncertainty.

r =........ ±........

A pulsar is a rapidly rotating neutron star that emits radio waves.

Describe the formation of a neutron star.

State one characteristic of a neutron star.

An astronomer uses a radio telescope to observe a pulsar.

The graph below shows the power that the telescope receives due to the radio waves from one full rotation of a pulsar.

By calculating the area between the curve and the horizontal axis, estimate the total energy received by the telescope in one full rotation of the pulsar.

The surface area of the telescope is about 3000 m². (ii)

The distance to the pulsar is about 300 pc.

By assuming that the radiation from the pulsar is emitted equally in all directions, estimate the total energy emitted in one full rotation.

A cloud is made up of droplets of water falling at terminal velocity.

Describe and explain the motion of an object falling at terminal velocity.

The terminal velocity v of a small sphere of density _s and radius r falling through a fluid of density _f is given by the formula:

where is a constant for the fluid and g is the acceleration of free fall.

Water droplets of rain fall to the ground whereas water droplets in mist appear to float.

Use the formula above to suggest why.

Large power stations generate an electrical power of about 1 GW.

Current methods of energy production that use nuclear fusion are unable to produce enough energy for large-scale energy production. A proposed method of controlling nuclear fusion is inertial confinement fusion (ICF). ICF uses a large number of powerful lasers to create the high temperatures required for nuclear fusion to occur.

One ICF experiment uses a network of capacitors to store the energy needed to power the lasers. When the network is fully charged:

• potential difference across the network = 24 kV

• total energy stored in the network = 400 MJ

Calculate the total capacitance, C, of the network.

Explain why the individual capacitors in the network should be connected in parallel in order to produce this total capacitance.

The total stored energy must be released in a time of less than 1 millisecond.

Explain, using a calculation, why the lasers are powered by the network of capacitors instead of being connected directly to the mains electricity supply.

The fusion reaction in the ICF experiment is

Calculate the number of fusion reactions that must occur for the energy released by fusion to be equal to the electrical energy stored in the network of capacitors.

• mass of deuterium = 2.014102 u

• mass of tritium = 3.016049 u

• mass of alpha particle = 4.002603 u

• mass of neutron = 1.008665 u

A 3D printer can manufacture small objects.

Some 3D printers use polylactic acid (PLA). PLA is supplied in the form of long filaments. The 3D printer melts the PLA and builds up the shape of the desired object in layers.

The electrical supply to the heater in the printer has an e.m.f., , of 12 V. The power of the heater is 40 W.

Calculate the resistance, R, of the heater.

The specific latent heat of fusion of PLA is 9.4 × 10⁴ J kg^–1 and its melting point is 160 °C. (b)

Define specific latent heat of fusion.

Calculate the maximum mass m of PLA that the heater could melt in one minute.

Explain why the printing process is slower in practice than your answer to (ii) suggests.

High-energy X-ray photons can destroy living cells. In radiotherapy, these photons are targeted at cancer cells.

The radiation dose is the amount of energy that a patient’s body absorbs from the high-energy X-ray photons.

Fig. 6.2 shows how this dose changes with depth below the surface of the skin.

The dose initially rises with depth because the high-energy X-ray photons produce electrons and positrons as they pass through the body. These electrons and positrons are quickly absorbed, increasing the dose.

Explain why high-energy X-ray photons produce electrons and positrons as they pass through the body.

*(ii) A 3D object called a bolus is used in radiotherapy for patients with skin cancer. A bolus targets the maximum radiation dose near the surface of the skin. So using a bolus makes the radiotherapy more effective.

A bolus can be made from PLA using a 3D printer. The bolus must fit the shape of the patient’s body exactly. This shape is found beforehand by giving the patient either a CAT scan or a PET scan.

• Explain how CAT scans and PET scans work.

• Discuss the advantages and disadvantages of having a scan to produce a bolus for radiotherapy.