Page No 218: - 12) ELECTRICITY

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Question 1:

Why does the cord of an electric heater not glow while the heating element does?

Answer:

The heating element of an electric heater is a resistor. The amount of heat produced by it is proportional to its resistance. The resistance of the element of an electric heater is very high. As current flows through the heating element, it becomes too hot and glows red. On the other hand, the resistance of the cord is low. It does not become red when current flows through it.

Question 2:

Compute the heat generated while transferring 96000 coulomb of charge in one hour through a potential difference of 50 V.

Answer:

The amount of heat (H) produced is given by the Joule’s law of heating as

Where,

Voltage, V = 50 V

Time, t = 1 h = 1 × 60 × 60 s

Amount of current, 

Therefore, the heat generated is  .

Question 3:

An electric iron of resistance 20 Ω takes a current of 5 A. Calculate the heat developed in 30 s.

Answer:

The amount of heat (H) produced is given by the joule’s law of heating as

Where,

Current, I = 5 A

Time, t = 30 s

Voltage, V = Current × Resistance = 5 × 20 = 100 V

Therefore, the amount of heat developed in the electric iron is .