Question

what is the value of hot resistance of a bulb rated as 100W/​

Answer 1

Generally electrical appliances such as an electric bulb, geyser, heater, etc. are rated with power and voltage. If a bulb is rated 100W - 250V, it means that when a bulb is lit on a 250V supply, it consumes 100 W of electric power. This means that, 100 Joules of electrical energy gets converted into heat and light energy in 1 second.

From this rating we can calculate the resistance of the filament of the appliance while it is glowing and also the current which flows through it.

SinceP= V²/R,R=V²/P

.

For the bulb rated as 100 W - 250 V, the resistance of its filament

R= V²/P=250²/100 = 625Ω

The resistance of the filament of a bulb is much less than this value when it is not lit because the resistance of a filament increases with the increasing temperature.

Answer 2

Answer:

The resistance of a bulb with given ratings would be 625 Ω.

Explanation:

Given - P = 100 W
            V = 250 V (usually, appliances of 100W come with a voltage rating of 250 V)
To find - The resistance of the bulb
Formula - $P = \frac{V^2}{R}$
            ⇒ $R = \frac{V^2}{P}$

Solution - $R = \frac{250^2}{100}$
                $R = \frac{250 \times 250}{100}$
                Solving this, we get
                $R = 625 \ohm$ ohm

Conclusion - The bulb's resistance is a lot lesser than the given value when not lit. It only increases with an increase in temperature (i.e., power consumption).
Also, we can conclude that the resistance of a bulb with given ratings would be 625 Ω.

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