Science
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Chapter: 12 Electricity
Class: X
Exercise 6
Question 1
Why does the cord of an electric heater not glow while the heating element does?
Answer 1
The heating element of an electric heater is a resistor. According to Joule’s law of heating, the amount of heat produced by it is proportional to its resistance.
H = I2Rt
The resistance of the heating element of an electric heater is very high. As current flows through the element, high amount of heat produced is very high which make it very hot and it glows red. On the other hand, the cord has low resistance and tt does not become hot and does not glow 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 2
Question 3
An electric iron of resistance 20 Ω takes a current of 5 A. Calculate the heat developed in 30 s.
Answer 3
According to Joule’s law of heating, the amount of heat produced is
H = V x I x t
Given:
I = 5 A
R = 20 Ω
t = 30 seconds
V =?
H =?
V = I x R = 5A x 20Ω = 100 V
H = 100 x 5A x 30 sec = 15000 J
H = 1.5 x 104 J
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