OCR GCSE Combined Science B (21st Century) Paper 7 June 2019 question paper

In the National Grid, what is the name of the devices that change the voltage?

Complete the sentences about the diagram. Use words from the list.

You may use each word once, more than once, or not at all.

decreased increased unchanged

At Point A, the potential difference (voltage) is........

At Point B, the potential difference (voltage) is........

Appliances can be connected to the mains electricity supply in homes using 3-pin plugs.

What is the potential difference (voltage) of the mains electricity in a home?

Amaya thinks of a hazard with using mains electricity.

Explain why Amaya is correct.

Alex is frying potatoes in oil. Ben is boiling potatoes in water.

Their teacher suggests they compare the specific heat capacities of oil and water.

Alex and Ben set up the apparatus shown in this diagram to measure the specific heat capacity of the oil.

Explain how they can safely use the apparatus, to take measurements, and to determine the specific heat capacity of the oil.

Alex and Ben repeat their experiment 3 times. Their results are shown in Table 2.1.

Calculate the mean specific heat capacity of the oil, using all the data in Table 2.1.

Mean specific heat capacity =........ kJ/kg °C

Table 2.2 shows accurate values for the specific heat capacities of the oil and water.

Compare the accurate value for the oil with Alex and Ben’s calculated value in (b).

Suggest a reason for the difference, and suggest how they could improve their experiment to get a more accurate result.

The diagram below shows a game that uses magnets.

When the stick is moved near the boat, the boat moves towards it.

Two students are discussing why the boat moves towards the stick.

Describe the difference between a permanent magnet and an induced magnet.

Describe what happens if the poles of two permanent magnets are brought close together:

When unlike poles are brought close together, they........

When like poles are brought close together, they........

Describe how the strength and direction of the magnetic field change around a bar magnet.

Add to the diagram to help you answer the question.

Beth has a magnetic compass. It always points to Earth’s magnetic north pole.

Explain what this tells you about the core of the Earth.

An ultrasound scanner makes images of unborn babies using sound waves with a frequency of 3.5 MHz.

Define frequency.

The ultrasound waves travel at a speed of 1540 m/s through the head.

Calculate the wavelength of the waves.

Use the equation: wave speed = frequency × wavelength

Give your answer in standard form.

Calculate the size of the baby’s head.

The diagram below shows how an aluminium sheet is compressed to make aluminium foil of the required thickness.

A detector measures how much radiation passes through the aluminium foil. A computer uses this measurement to calculate the thickness of the foil.

Americium-241 and promethium-147 are radioactive isotopes used in industrial processes.

Complete the decay equations for these isotopes.

Which of these two isotopes, americium-241 or promethium-147 is most suitable for measuring the thickness of the aluminium foil?

Explain your answer.

The radioactive source has a safety-shutter at the front which is closed when it is not in use.

Explain why the safety-shutter is needed.

A London Underground train travels on a level track inside a tunnel.

The brakes are applied at point B. The train stops at point P.

The braking force is 2.3 × 10⁵ N and the work done by the braking force is 4.6 × 10⁷ J.

Calculate the distance, d.

Describe the main energy transfers that take place when the train slows to a stop.

The total mass of the train and passengers is 280 000 kg.

Calculate the force required to accelerate the train from rest to a speed of 12 m/s over a distance of 56 m.

Use the equation: kinetic energy = ½ × mass × speed²

When the underground train system was built, the temperature of the air in the tunnels was about 14 °C.

Today it is about 23 °C and cooling systems are required.

Suggest why the temperature of the air in the tunnels has increased.

Jamal is choosing a lamp that emits coloured light.

He looks at a lamp which has a white light at the centre and glass prisms surrounding it. Each prism produces a spectrum.

Jamal knows this is because the light is refracted when it moves from air to glass and from glass to air.

Explain what happens to the light that causes it to be refracted when it enters and leaves a glass prism.

A cheetah is the fastest land mammal. Cheetahs hunt gazelles.

A cheetah has a maximum speed of 110 km/h.

Determine the cheetah’s maximum speed in metres per second.

Give your answer to 2 significant figures.

Explain the difference between a vector and a scalar quantity.

Which of the quantities below are vectors and which are scalars ?

Tick one box in each row.

Fig. 9.1 shows a speed-time graph of a gazelle which starts moving.

Use Fig. 9.1 to calculate the deceleration of the gazelle.

Use Fig. 9.1 to calculate the distance the gazelle travels as it decelerates.

A second gazelle starts moving at the same time. The table below describes its motion.

Plot a graph on Fig. 9.1 for the motion of the second gazelle.

Without further calculation, judge which gazelle travelled furthest.

Explain your answer.

The diagram shows a copper rod in a magnetic field.

The copper rod is 0.25 m long and weighs 0.63 N. The entire length of the copper rod is on a horizontal table in a magnetic field of flux density 1.8 T.

The magnetic field is at right angles to the table and the copper rod.

The copper rod is connected to an electric circuit which is switched on, and the current is slowly increased.

Calculate the current needed to cause a force on the copper rod equal to its weight.

Buildings need heating and cooling systems.

Describe the changes that take place when a liquid is heated, and then changes state from liquid to gas.

Use ideas from the particle model in your answer.

In a sustainable office building, water is circulated to keep the building cool in the day.

This water is cooled by passing through a tank containing stainless steel spheres. Inside the spheres there is a material called a phase change material (PCM) that melts when the water is warm.

When the water is cooled by the night air it freezes the PCM again.

Describe how the energy transfers involved help to cool the building at night.

The ideal building temperature is 22 °C.

Which PCM, A or B, is more suitable for cooling the building? Justify your answer.

Calculate the specific latent heat of PCM B.