Efficiency

Figure 17 shows solar panels in a field on a small remote island.

The solar panels provide electricity to a small village.

Use the Physics Equations Sheet to answer questions 10.2 and 10.3.

Which equation links efficiency, total power input and useful power output?

Tick () one box.

efficiency = total power input × useful power output

On a cloudy day, the total power input to the solar panels is 250 000 W.

The efficiency of the solar panels is 0.20

Calculate the useful power output of the solar panels.

Figure 18 shows during one day:

the electrical power demand of the village

the electrical power output of the solar panels.

Determine for how much time the electrical power demand was greater than the electrical power output.

A large battery is used to store excess energy from the solar panels.

The battery transfers power to the village when the power output of the solar panels is less than the demand.

The village is not connected to the National Grid.

Explain why the village needs the solar panels and the battery for a continuous electricity supply.

Use information from Figure 18.

Figure 4 shows solar panels in a field on a small remote island.

The solar panels provide electricity to a small village.

Use the Physics Equations Sheet to answer questions 03.2 and 03.3.

Which equation links efficiency, total power input and useful power output?

Tick () one box.

efficiency = total power input × useful power output

On a cloudy day, the total power input to the solar panels is 250 000 W.

The efficiency of the solar panels is 0.20

Calculate the useful power output of the solar panels.

Figure 5 shows during one day:

the electrical power demand of the village

the electrical power output of the solar panels.

Determine for how much time the electrical power demand was greater than the electrical power output.

A large battery is used to store excess energy from the solar panels.

The battery transfers power to the village when the power output of the solar panels is less than the demand.

The village is not connected to the National Grid.

Explain why the village needs the solar panels and the battery for a continuous electricity supply.

Use information from Figure 5.

Energy resources are renewable or non-renewable.

Which two of the following energy resources are renewable?

Tick (✓) two boxes.

Biofuel

Coal

Nuclear

Oil

Wind

Figure 5 shows wind turbines in the countryside.

What are two effects on the environment of using wind turbines to generate electricity?

Tick (✓) two boxes.

Some birds are killed by wind turbines.

There is no fuel cost when using wind turbines.

Wind is an unreliable energy resource.

Wind turbines generate lots of electricity in windy conditions.

Wind turbines produce low frequency noise.

Figure 6 shows a wind turbine.

The useful power output of the generator in the wind turbine is 144 000 W.

The efficiency of the wind turbine is 0.30

Calculate the total power input to the wind turbine.

Use the equation:

Use the Physics Equations Sheet to answer Questions 05.4 and 05.5.

Which equation links current, potential difference and power?

Tick (✓) one box.

power = potential difference × current

The power output of the generator in the wind turbine is 144 000 W.

The potential difference across the generator is 960 V.

Calculate the current in the generator.

Figure 7 shows how the National Grid links the wind turbine to consumers.

The step-up transformer increases the potential difference and decreases the current.

What effect does decreasing the current have on the energy loss from the power cables?

Tick (✓) one box.

The energy loss decreases.

The energy loss is not affected.

The energy loss increases.

What is the function of the step-down transformer in Figure 7 ?

Tick (✓) one box.

To decrease the current.

To decrease the potential difference.

To decrease the power input.

Figure 7 shows a student driving a bumper car at a theme park.

Figure 8 shows how the speed of the bumper car changed during a time of 20 seconds.

Estimate the distance travelled by the bumper car during the 20 seconds.

The bumper car motor has an efficiency of 80%.

The useful power output of the motor is 220 W.

Calculate the total power input to the motor.

Use the Physics Equations Sheet.

A bumper car collides with a stationary barrier and stops.

The student is wearing a seatbelt.

Explain how the seatbelt stops the student moving.

When the bumper car collided with the barrier, the bumper car came to a stop in a time of 600 ms.

The deceleration of the student was 2.0 m/s².

Calculate the initial velocity of the student.

Use the Physics Equations Sheet.

Figure 17 shows a desk lamp connected to the mains electricity supply.

The desk lamp is fitted with a high-efficiency LED bulb.

What does ‘high-efficiency’ mean?

Tick (✓) one box.

A large proportion of the total energy input is destroyed.

A large proportion of the total energy input is usefully transferred.

A large proportion of the total energy input is wasted.

The LED bulb wastes energy as thermal energy.

How does the thermal energy affect the temperature of its surroundings?

The output power of the lamp is 2.8 W.

Calculate the energy transferred by the lamp in 60 seconds.

Use the equation:

energy transferred = power × time

Mains electricity can be dangerous.

Table 2 shows information about the effects of different electrical supplies on the human body.

ac is alternating current.

Compare the effects on the human body of 50 Hz ac with 10 000 Hz ac.

Use data from Table 2.

Ten-pin bowling is a game where a ball is rolled along the floor to knock over some wooden pins.

Figure 1 shows a person ten-pin bowling.

The speed of the ball was 8.0 m/s just after leaving the person’s hand.

The mass of the ball was 5.5 kg.

Calculate the kinetic energy of the ball.

Use the equation:

kinetic energy = 0.5 × mass × (speed)²

When the ball collides with the pins, energy is conserved.

What is meant by ‘conservation of energy’ when the ball collides with the pins?

Tick (✓) one box.

The gravitational potential energy of the pins is the same before and after the collision.

The kinetic energy of the ball is the same before and after the collision.

The total energy of the ball and pins is the same before and after the collision.

A machine returns the ball to the person.

The machine takes 25.0 s to return the ball to the person.

The useful power output of the machine is 660 W.

Calculate the work done by the machine in returning the ball to the person.

Use the equation:

work done = power × time

The machine has an efficiency of 0.60

The useful power output of the machine is 660 W.

Calculate the total power input to the machine.

Use the equation:

The machine has several moving parts.

What is the name of the force caused by the moving parts rubbing together?

What happens to the wasted energy from the machine?

Tick (✓) one box.

The wasted energy cools the surroundings.

The wasted energy heats the surroundings.

The wasted energy is destroyed.

An energy input of 1.3 × 10¹⁸ J is supplied each year by power stations to the National Grid.

Not all of this energy is supplied to consumers. Some of the energy is wasted in the distribution process.

Write the equation which links efficiency, total input energy transfer and useful output energy transfer.

The energy supplied each year to consumers is 1.2 × 10¹⁸ J

Calculate the efficiency of the distribution process.

How is electrical power transmitted across the National Grid to make the process as efficient as possible?

Tick one box.

Write the equation which links energy transferred, power and time.

A wind turbine supplies a power output of 8000 kW for 1200 seconds.

Calculate the energy transferred by the wind turbine in kJ

Describe the environmental advantages and disadvantages of using wind turbines to generate electricity in the UK.