Question

A bulb is rated at 200V-100W. What is it's resistance? Five such bulbs burn for 4 hours. What is the electrical energy consumed? Calculate the cost if the rate is 4.60 ruppes per unit.

Answer 1

Here, Power (P) = 100 watts = (100/1000)kilowatts
=0.1 kw

Voltage (V) = 200 Volts

Time (t) = 4 hrs.

We know that

Power = P = $\frac{V^2}{R}$

$\Rightarrow R=\frac{V^2}{P}$

$\Rightarrow R=\frac{{200}^2}{100}=\frac{40000}{100}=400\Omega$

$Also,E=P\times t$

$E=100\times 4\times 60\times 60=1.44\times {10}^{6}J$

.: Energy consumed by each bulbs = $\frac{1.44\times {10}^6}{3.6\times {10}^6}$ = 0.4 KWh.

total energy in units = $5\times 0.4$ = 2 units

Since the cost of 1 unit of electricity = Rs. 4.60

Therefore, Cost of 2 units of electricity = 4.60 x 2 = Rs 9.20