Question

Several electric bulbs designed to be used on a 220 V electric supply line, are rated 10 W. How many lamps can be connected in parallel with each other across the two wires of 220 V line if the maximum allowable current is 5 A?

• A. 110
• B. 580
• C. 220
• D. 50

Answer 1

The correct option is A

110

Resistance of each bulb, r = $\frac{V^2}{P}$ = $\frac{{220}^2}{10}$ = 4840 Ω

Total resistance in the circuit, R =$\frac{220V}{5A}$ = 44 Ω

Let n be the number of bulb (each of resistance r) to be connected in parallel to obtain a resistance R.

Clearly, R = $\frac{r}{n}$ or n = $\frac{r}{R}$ = $\frac{4840\Omega }{44\Omega }$ = 110