Edexcel IGCSE Physics (b) Mains electricity Question Bank

power = current x voltage

Accept:
- standard symbols, e.g. P = I x V

Ignore:
- C or c for current

- substitution
- evaluation
- unit

Example:
- P = 9.6 x 230
- P = 2200
- unit = watts / W

The coil has resistance. When current flows, electrons transfer energy to the lattice ions by collisions, increasing the thermal store/temperature of the coil.

Marking points:
- substitution into formula
- conversion from $\mathrm{mA}$ to $\mathrm{A}$
- evaluation to 2 or more significant figures

Example:
$$P=230\times22\times10^{-3}$$$$P=230\times0.022$$$$P=5.1\ \mathrm{W}$$

Accept:
- $5.06\ \mathrm{W}$
- 0.022 or $\div1000$ seen anywhere in working

Ignore:
- units

Marking guidance:
- Condone a calculation of current or voltage given to at least 3 significant figures using a power of $5\ \mathrm{W}$ for full marks.

Marking points:
- substitution into $P=\frac{E}{t}$
- rearrangement
- evaluation

Example:
$$5=\frac{E}{30}$$$$E=5\times30$$$$E=150\ \mathrm{J}$$

Accept:
- ECF from 7(b)(ii)
- $$E=230\times22\times10^{-3}\times30$$
- 151.8, 152, or $153\ \mathrm{J}$
- use of E=VIt or other valid methods

Marking guidance:
- Deduct 1 mark for power-of-ten error.