A coil of wire is suspended between the poles of a magnet. The coil consists of 30 turns of insulated wire and is connected in series with a variable resistor and a DC power supply.
Which of the following modifications would result in a decrease in the turning effect on the coil?
replacing the permanent magnet with a weaker magnet
decreasing the resistance of the variable resistor
increasing the number of turns in the coil to 50
increasing the voltage of the power supply
31 exam-style questions on CIE IGCSE Physics 4.5.5 The d.c. motor. Each one has a worked solution and a mark scheme showing where the marks go.