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Practice each question, then open the answer or worked solution.
Why does the cord of an electric heater not glow while the heating element does?
The heating element of an electric heater is made of an alloy which has a high resistance. When the current flows through the heating element, the heating element becomes too hot and glows red. The cord is usually made of copper or aluminum which has low resistance. Hence the cord doesn’t glow.
Compute the heat generated while transferring 96000 coulomb of charge in one hour through a potential difference of 50 V.
The heat generated can be computed by Joule’s law as follows:
H = VIt
where,
V is the voltage, V = 50 V
I is the current
t is the time in seconds, 1 hour = 3600 seconds
The amount of current can be calculated as follows:
2. An electric iron of resistance 20 Ω takes a current of 5 A. Calculate the heat developed in 30 s.
The amount of heat generated can be calculated using the Joule’s law of heating, which is given by the equation
H = VIt
Substituting the values in the above equation, we get,
H = 100 × 5 × 30 = 1.5 × 104 J
The amount of heat developed by the electric iron in 30 s is 1.5 × 104 J.