Question

A bulb is rated at 230V- 100W. What is its resistance? Two such bulbs are switched-on for 4 hours continously. How much electrical energy is consumed by these two bulbs together?

• A. $592\Omega ,1.44\times$ ${10}^{5}J$
• B. $529\Omega ,1.44\times {10}^{4}J$
• C. $592k\Omega ,1.44\times {10}^{5}J$
• D. $529\Omega ,1.44\times {10}^{5}J$

Answer 1

The correct option is D

$529\Omega ,1.44\times {10}^{5}J$

Given: voltage, V = 230 volts, power consumed, P = 100 watts,
time, t = 4 hours.
Let the resistance of the bulb = R.
So using, $P=\frac{V²}{R}$,
$R=\frac{V²}{P}$
$=\frac{230²}{100}=529\Omega$.
Now, energy consumed = heat generated, $H=\frac{V²}{R}$ $\times$ t

t = 4 hours = 4 $\times$ 3600 = 14400 s.

So, $H=\frac{230²}{529}$ $\times$ 14400

Therefore, $H=1.44\times {10}^{5}J$.