Question

Q.14 Two appliances of rating 200
watt-250 volts and 100 watt-250
volts are joined in series to a 250
volts supply. Total power consumed
in the circuit is​

Answer 1

For bulb 1

P = 200 watt

V = 250 V

I = P/V

I = 200/250

I = 0.8 A

R = V/I

R = 250/0.8

R = 312.5 ohm

For bulb 2

P = 100 watt

V = 250 V

I = P/V

I = 100/250

I = 0.4 A

R = V/I

R= 250/0.4

R = 625 ohm

Total resistance in circuit = 625 + 312.5

= 937.5 ohm

Total power consumed, P = V²/R

= 250 × 250/937.5

= 66.66 watt or 67 watt

Answer 2

Answer:

Normally it is a common feeling that we are adding two bulbs in series and so their consumption should add up. But, when we make a series connection, both the bulbs do not get 250V because of voltage drop for series connection.

Power varies in square of the available voltage across the terminals of the bulb. In practical life also when you add the bulbs in series you see the glow is diminished as voltage available at the terminals are much less than the supply voltage.

For the given problem calculate the resistance of the bulbs by R=V^2/W. Get the series current by I= 250/(R1+R2) and then calculate total power by W=I^2*(R1+R2).

Thanks for asking.