Question

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

Answer 1

Here, potential difference, V = 220 V

Resistance of each coil, r = 24 $\Omega$

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

(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, i.e., $I_s$ = $\frac{V}{R_s}$ = $\frac{220V}{48\Omega }$= 4.6 A

(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, i.e, $I_p$ = $\frac{V}{R_p}$ = $\frac{220V}{12\Omega }$ = 18.3 A