The copper coil of an electric door lock is connected across a constant 12 V supply. Its resistance is 24 Ω when it is cold and 30 Ω after it has warmed up.
How does the power of the coil change as it warms up?
It decreases by 1.2 W1.2\ \mathrm{W}1.2 W.
It decreases by 0.10 W0.10\ \mathrm{W}0.10 W.
It increases by 1.5 W1.5\ \mathrm{W}1.5 W.
It increases by 1.2 W1.2\ \mathrm{W}1.2 W.
105 exam-style questions on Edexcel GCSE Physics 10.3 Electrical energy and power, covering 10.3.1 The heating effect of an electric current, 10.3.2 Reducing energy transfer in wires, 10.3.3 Advantages and disadvantages of the heating effect, 10.3.4 Energy transferred by an electrical circuit, 10.3.5 Electrical power, and 10.3.6 Energy transfers in domestic devices. Each one has a worked solution and a mark scheme showing where the marks go.