Chapter 11 Electricity Questions-06
QUESTIONS
1. Why does the cord of an electric heater not glow while the heating element does?
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Answer
The heating element of the heater is made up of alloy which has very high resistance so when current flows through the heating element, it becomes too hot and glows red. But the resistance of cord which is usually of copper or aluminium is very law so it does not glow.
2. Compute the heat generated while transferring 96000 coulomb of charge in one hour through a potential difference of $50 V$.
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Answer
Given Charge, $Q=96000 C$
Time, $t=1 hr=60 \times 60=3600 s$
Potential difference, $V=50$ volts
Now we know that $H=$ VIt
So we have to calculate / first
As $l=Q / t$
$\therefore I=96000 / 3600=80 / 3 A$
$ H=50 \times \dfrac{80}{3} \times 60 \times 60=4.8 \times 10^{6} J $
Therefore, the heat generated is $4.8 \times 10^{6} J$.
3. An electric iron of resistance $20 \Omega$ takes a current of $5 A$. Calculate the heat developed in $30 s$.
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Answer
The amount of heat $(H)$ produced is given by the joule’s law of heating as $H=Vlt$ Where, Current, $I=5 A$
Time, $t=30 s$
Voltage, $V=$ Current $\times$ Resistance $=5 \times 20=100 V$
$H=100 \times 5 \times 30=1.5 \times 10^{4} J$.
Therefore, the amount of heat developed in the electric iron is $1.5 \times 10^{4} J$.
