Question

A potential difference of 220 V is applied across the 100 W bulb. Find:
1. Power
2. Current flowing through it
3. Resistance of the filament of the bulb
4. Electric Energy consumed by it in 10 sec.
5. How much will be the cost of bill. If the rate is Rs. 4.2 per Joule.

Answer 1

1) power = i^2R
where i is current and R is resistance
now,
but bulb consume 100 w power in 220 volt so,
power =100 watt

2) use above formula ,
p=i^2R
we also know ,
v=iR
so, R=v/i
hence ,
p=vi
100=220 x i
i=10/22=5/11 A

3) v=iR
220 = 5/11 x R
R = 220 x 11 /5 =484 ohm

4) energy = power x time
=100 x 10 = 1000 joule

5) cost = rate x energy
=4.2 x 1000 = 4200 Rs

Answer 2

1)Power = 100W

2) current = P/V
= 100/220
= 5/11 A

3)Resistance = V^2/P
= (220)^2/100
=484 ohm

4)1 s = 1/3600 hr
10 s = 10/3600 hr
= 1/360 hr
energy = P x t
= 100 x 1/360 Wh
=10/36 Wh

5)1Wh = 3600 J
10/36 Wh =( 3600 x 10/36 )J
= 1000 J
Cost = 1000 x 4.2 = Rs 4200