Question

Two lamps one rated 100w at 220v and other 60w at 220v are connected in parallel to electric mains of 220v.find the current drawn by the bulbs from the mains

Answer 1

Given,

In case of Bulb 1

Potential difference,V1= 220v

Power,P1 = 100w

In case of Bulb 2

Potential Difffernce,D2 =220v

Power,P2 = 60w

Now, since they are connected in parallel combination hence they have same potential difffernce and the total Current in the circuit is given the sum of currents flowing in both the resistors.

Power = Potential difference×Current

=>P = V×I

=>I= P/V.

Now,In case of Bulb 1

I1 = 100/220

=> I1 = 5/11 watts ------------(i)

Now,in case if bulb 2

I2 = 60/220

=>I2= 3/11watts ---------------(ii)

From (i) and (ii) we get=>

Total Current in circuit,(I)n=>

(I)1 + (I)2

=>(3/11)+(5/11)

=>8/11 watts.

Hence, the current in the circuit is 8/11 watts or 0.73 watts which is drawn from mains.

Remember

1)Ohm's law of resistance

V=I×R(Vis directly proportional to I)

2) Power = Work/Time

or

Power = V×I = I^2×R = V^2/R