Physics Paper 1 Mistakes

A student investigated how the current in a filament lamp varied with the potential difference across the filament lamp.

A second student did the same investigation. The ammeter used had a zero error.

What is meant by a zero error? [1 mark]

Ammeter displays a reading when not connected to a circuit.

Figure 3 shows an LED torch.

The torch contains one LED, one switch and three cells.

When replaced, the cells were put into the torch the wrong way around.

Explain why the torch did not work. [2 marks]

• There is no current in a diode in the reverse direction

  • because a diode has a high resistance in the reverse direction

Write down the equation which links density (ρ), mass (m) and volume (V). [1 mark]

$$\rho=\frac{m}{V}$$

density = mass ÷ volume

Give two environmental advantages of using a gas-fired power station to generate electricity compared with using a coal-fired power station. [2 marks]

• No sulfur dioxide so no acid rain

• No particulates released so no global dimming

A thermistor can be used to measure temperature.

Figure 8 shows how the resistance of four different thermistors A, B, C and D, varies with temperature.

Which of the four thermistors would be the most suitable to measure the surface temperature of the sea?

Explain your answer. [3 marks]

• C

  • the change in resistance is greatest between 0 and 25ºC

Radioactive waste from nuclear power stations is a man-made source of background radiation.

Give one other man-made source of background radiation. [1 mark]

X-rays

Nuclear fission releases energy.

Describe the process of nuclear fission inside a nuclear reactor. [4 marks]

• Neutron absorbed by a uranium nucleus

• Nucleus splits into two parts

• 2 - 3 neutrons are released

• Gamma rays are emitted

Explain how the process of nuclear fusion leads to the release of energy. [2 marks]

• Lighter nuclei join to form heavier nuclei

• Some mass of the nuclei is converted to energy

Nuclear fusion power stations will produce radioactive waste.

This waste will have a much shorter half-life than the radioactive waste from a nuclear fission power station.

Explain the advantage of the radioactive waste having a shorter half-life. [2 marks]

• Activity decreases quickly

  • so doesn’t need to be buried underground for as long

Figure 9 shows a theme park ride called AquaShute.

Riders of the AquaShute sit on a sled and move down a slide.

A light gate and data logger can be used to determine the speed of each rider and sled.

What two measurements are needed to determine the speed of a rider and sled? [2 marks]

• Gravitational field strength

• Length of sled

• Mass of rider and sled

• Temperature of surroundings

• Time for sled to pass light gate

• Length of sled

• Time for sled to pass light gate

Figure 9 shows a theme park ride called AquaShute.

Riders of the AquaShute sit on a sled and move down a slide.

At the bottom of the slide, all riders and their sleds have approximately the same speed.

Explain why. [4 marks]

• ½mv² = mgh

• v² = 2gh

• Final speed depends on vertical height and gravitational field strength

• Variations will be due to friction

An electric kettle was switched on.

Figure 10 shows how the temperature of the water inside the kettle changed.

The straight section of the line in Figure 10 can be used to calculate the useful power output of the kettle.

Explain how. [3 marks]

• gradient = ∆θ ÷ t

• Pt = mc∆θ

• P = gradient × mc

A student investigated how the total resistance of identical resistors connected in parallel varied with the number of resistors.

The student used an ohmmeter to measure the total resistance of the resistors.

Figure 11 shows the student’s circuit with 3 resistors.

The student repeated each reading of resistance three times.

Table 1 shows some of the results for 3 resistors in parallel.

Number of resistors	Reading 1 (ohms)	Reading 2 (ohms)	Reading 3 (ohms)	Mean (ohms)
3	15.8	15.3	X	15.7

The student thought that taking a fourth reading would improve the precision of the results.

The fourth reading was 16.2 Ω.

Explain why the student was wrong. [2 marks]

• Precise results show little variation

• The 4th result is further away from the mean than the other values

A student investigated how the total resistance of identical resistors connected in parallel varied with the number of resistors.

The student used an ohmmeter to measure the total resistance of the resistors.

Figure 12 shows the results from the investigation.

The student concluded that the number of resistors in parallel was inversely proportional to the mean total resistance.

Explain why the student was correct. [3 marks]

Use data from Figure 12 in your answer.

• n × R = constant

  • 2 × 24 = 48

  • 3 × 16 = 48

  • 4 × 12 = 48

Explain why adding resistors in parallel decreases the total resistance. [2 marks]

• Multiple paths for electrons to flow

• Total current is greater

Figure 13 shows part of a mains electricity lighting circuit in a house.

A fault in the switch caused a householder to receive a mild electric shock before a safety device switched the circuit off.

An electrician replaced the switch.

The electrician would have received an electric shock unless the circuit was disconnected from the mains supply.

Explain why. [3 marks]

• One wire in the switch is live

• The electrician is earthed

  • so there will be a large potential difference between the live wire and the electrician

The current from an electric shock causes a person’s muscles to contract.

The person cannot let go of the electrical circuit if the current is too high. Figure 14 shows how the maximum current at which a person can let go depends on the frequency of the electricity supply.

The UK mains frequency is 50 Hz.

Explain why it would be safer if the UK mains frequency was not 50 Hz. [2 marks]

• 50Hz has the lowest maximum let-go current

• Lower or higher mains frequency would allow a person to let go at higher currents

The temperature of the helium in a balloon was increased.

The mass and volume of helium in the balloon remained constant.

Explain why the pressure exerted by the helium inside the balloon would increase. [4 marks]

• Particles would have a higher mean kinetic energy

  • so increased collisions with the walls of the balloon per second

• Greater forces exerted in collisions

• Greater force exerted on the same area

Figure 2 box shows the equipment a student used to determine the specific heat capacity of iron. 

The iron block the student used has two holes, one for the heater and one for the thermometer.

Before the power supply was switched on, the thermometer was used to measure the temperature of the iron block. 

The student left the thermometer in the iron block for a few minutes before recording the initial temperature.

Suggest why. [1 mark]

So the thermometer temperature was the same as the temperature of the metal block

What is meant by ‘direct potential difference’? [1 mark]

Polarity of the potential difference doesn’t change

The electrical circuit was left switched on while the ice changed from a solid to a liquid and increased in temperature to 5 °C.

Explain the changes in the arrangement and movement of the particles as the ice melted and the temperature increased to 5 °C. [6 marks]

• Particles in a solid are in a regular pattern

• Particles in a liquid are in a random arrangement

• Particles in a solid are vibrating about fixed positions

• Particles in a liquid are moving freely

• As ice changes state to water the temperature remains constant as the potential energy of the particles increases

• As the temperature increases the particles move faster so the kinetic energy of the particles increases

Figure 5 shows how the power output of the generator varied during one year.

A solar power system is installed in the remote village in addition to the hydroelectric generator.

Explain why this improves the reliability of the electricity supply to the village. [2 marks]

Use information from Figure 5.

• In the summer months the power output is lower but it would be higher with a solar power system

  • So there is less variation in total power output

Carbon-14 is a radioactive isotope.

Carbon-14 has a half-life of 5700 years.

What does ‘a half-life of 5700 years’ mean? [1 mark]

Time it takes for the radiation emitted to halve

Table 1 gives the half-life of some other radioactive isotopes.

A sample of fluorine-17 has an activity that is one quarter of its original activity.

Calculate the age of the sample of fluorine-17. [2 marks]

• 2 half lives

• 64.37 × 2 = 128.74

Table 1 gives the half-life of some other radioactive isotopes.

All of the isotopes in Table 1 emit beta radiation.

Explain which isotope would cause the biggest risk to a person’s health based only on the half-life of each isotope. [3 marks]

• Nitrogen-18

• Greatest activity

• Greatest dose of radiation absorbed

A student investigated how the current in a filament lamp varies with the potential box difference across the filament lamp.

Figure 6 shows the results

Describe a method the student could use to obtain these results. [6 marks]

You should include a circuit diagram.

• Turn on the power supply and measure the current using an ammeter and the p.d. using a voltmeter

• Adjust the variable resistor and record the readings again

  • range of p.d. 0 to 6V

  • in intervals of 1V

• Repeat step 2 to get several readings

• Swap the connections on the power supply to get negative values

• Repeat steps 2 and 3

• Calculate a mean and discard anomalies

A student investigated how the current in a filament lamp varies with the potential box difference across the filament lamp.

Figure 6 shows the results

The power output of the lamp is 1.0 W when the potential difference across the lamp is 5.0 V.

A student predicts that the power output would be 4.0 W if the potential difference was doubled.

Explain why the student is not correct. [2 marks]

• The current and the p.d. would both need to double

  • but the graph doesn’t show direct proportionality

A baby bouncer is a harness attached to a spring that hangs from a door frame.

Figure 7 shows a baby in a baby bouncer in two positions.

The baby bouncer should not be used with babies that have a mass greater than 12 kg.

Suggest one reason why. [1 mark]

Spring may become permanently extended