Question

A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of 24$\Omega$ resistance, which may be used separately, in series, or in parallel. What are the currents in the three cases? [3 MARKS]

Answer 1

Each point: 1 Mark


Here, potential difference, V = 220 V
Resistance of each coil, $r=24\Omega$

(i) When each coils A or B is connected separately, current through each foil, i.e.,
$I=\frac{V}{r}=\frac{220}{24}=9.2A$

(ii) When coils A and B are connected in series, equivalent resistance in the circuit,
$R_s=r+r=2r=48\Omega$

Current through the series combination, ie e, $I_s=\frac{V}{R_x}=\frac{220V}{48\Omega }=4.6A$

(iii) When the coils A and B are connected in parallel, equivalent resistance in the circuit,
$R_p=\frac{r}{2}=\frac{24\Omega }{2}=12\Omega$

Current through the parallel combination, ie. e,
$I_p=\frac{V}{R_v}=\frac{220V}{12\Omega }=18.3A$