Practise Edexcel IGCSE Physics investigation variables by identifying what changes, what is measured and what must be controlled in practical methods.
A student uses this apparatus to investigate how the efficiency of an electric motor varies with its input voltage.
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.
Give two control variables for the investigation.
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