Physics 5054 · O Level · Electrical safety

Electrical safety — practice question

Fig. 5.1 shows a section of a circuit with a $240\,\text{V}$ a.c. mains supply linked to a lamp and two heaters with resistances of $40\,\Omega$ and $60\,\Omega$.
(a)[1]

Complete Fig. 5.1 by drawing the symbol for a fuse in the gap in the circuit.

(b(i))[1]

On Fig. 5.2 sketch the current-voltage graph of a filament lamp.

(b(ii))[2]

Explain why the current-voltage graph you drew in (i) has that shape.

(c)[3]

Calculate the current at point P in the circuit diagram in Fig. 5.1.

(d(i))[1]

The lamp current is $1.5\,\text{A}$. Suggest an appropriate fuse rating for the fuse.

(d(ii))[2]

Explain why a fuse rating that is much greater than the value in (i) is unsuitable.

(d(iii))[1]

Explain why a fuse must be connected in the live wire instead of the neutral wire or earth wire.

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