Question

1. An electric bulb is rated at 200 V; 100 W. What is its resistance?
2. Calculate the energy consumed by 3 such bulbs if they glow continuously for 10 hours for complete month of November.
3. Calculate the total cost if the rate is ₹ 6.50 per unit.

Answer 1

(a) Given, V = 200 volts and P  = 100 watt

As P = `"V"^2/"R"`

Or R = `"V"^2/"R"`

= `(200)^2/(100  "W")`

= `40000/(100  Ω)`

= 400 Ω

(b) Electrical energy consumed, E = number of units × Power of each unit × time × total days

Here, n = 3, P = 100 W, t = 10 hours, Days = 30

So, E = 3 × 100 W × 10 h × 30

= 90,000 Wh

= 90 kWh

(c) Total cost of electricity = Total unit of energy consumed × Cost per unit

= 90 kWh × 6.50

= ₹ 585