Question

calculate the ratio of resistance of a 50w bulb and a 25w bulb

Answer 1

Answer:

Let us assume that Potential difference applied across the two lamps is same.

The relation between power and resistance is given by,

P= V2/R

Thus, from this we can say that power is inversely proportional to resistance.

So more the power, less is the resistance.

Thus,

For lamp with power 50 Watt resistance is less than that with lamp 25 Watt.

Consider the resistance of bulb with power 25 W as R1 and that of bulb with power 50 W be R2 .

As the voltage is constant we can take the ratio of the power of bulb

Answer 2

Explanation:

P1 = 50W

P2 = 25W

R

R'

assumption : Voltage is constant

P1 = V²/R => R = V²/P1

P2 = V²/R' => R' = V²/P2

R/R' = (V²/P1) / (V²/P2)

=> R/R' = P2/P1 (V² gets cancelled)

=> R/R' = 25/50

=> R/R' = 1/2

Therefore R : R' = 1 : 2