Question

Two bulbs have ratings 100w 220v and 60w 220v. which one has a greater resistance

Answer 1

Power = Voltage ^2 / resistance
Resistance = voltage^2/ power
R= 220^2/100 = 48400/100 = 484 ohms
R= 220^2/60 = 48400/60 = 806 ohms
The bulb with rating 60 W and 220 V has greater resistance.
You can do it directly by recognising that power is inversely proportional to resistance as voltage is constant. Hence, the bulb which requires more power will have less resistance and the one which requires less power will have greatest resistance

Answer 2

Answer:

Explanation:

Given :-

Two bulbs have rating 100W, 220V and  60W, 220V.

To Find :-

Which one has the greatest  resistance.

Formula to be used :-

P = V²/R

Solution :-

Putting all the values, we get

For Bulb A

⇒ 100 = (220×220)/R₁

⇒ R₁ = 484 ohm

For Bulb B

⇒ 60 = (220 × 220)/R₂

⇒ R₂  = 806.6 ohm

Hence, bulb B having 60W, 220V will have greater resistance.

Terms to be known :-

P is power in Watt (W) .

R is resistance in ohm .

V is voltage in volts (V) .