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Edexcel IGCSE Physics 4.4 Efficiency Equation Questions

Use the efficiency percentage to compare devices and calculate useful, total or wasted energy in heaters, motors, transformers or power stations.

Syllabus
First assessment 2019
Course
Physics 4PH1

Exam points

  • Use efficiency = useful energy output ÷ total energy output × 100%, rearranging to find a missing quantity.
  • Calculate efficiency from a device’s measured useful and total energy or power values.
  • Find wasted energy from an efficiency and useful output, or as total output minus useful output.
  • Interpret an efficiency percentage as the useful share of total output when comparing devices.

Edexcel IGCSE Physics 4.4 Efficiency Equation Questions question 1

[Maximum number: 3]

A student uses this apparatus to investigate how the efficiency of an electric motor varies with its input voltage.

Figure for Question Edexcel IGCSE Physics 4.4 Efficiency Equation Questions question 1 — Edexcel IGCSE Physics

This is the student's method.
- connect the electric motor to a d.c. power supply and a joulemeter
- attach a 1.0 kg mass to the electric motor using a length of string
- set the voltage of the power supply to 10 V and switch on the power supply
- switch off the power supply when the mass has been lifted through a distance of 50 cm
- record the input energy to the motor from the joulemeter
- calculate the energy transferred to the gravitational store of the mass
- calculate the efficiency of the motor

The student repeats this process, setting the power supply to a different voltage each time.

The table shows the student's results.

Table for Question Edexcel IGCSE Physics 4.4 Efficiency Equation Questions question 1 — Edexcel IGCSE Physics

Calculate the motor efficiency when the power supply is set to a voltage of 10 V.

efficiency = ............ %

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