An electric bulb rated for $500\, watts$ at $100\, volts$ is used in a circuit having a $200-volt$ supply. The resistance $R$ that must be put in series with the bulb, so that the bulb draws $500\, W$ is .................. $\Omega$
A$10$
B$20$
C$50$
D$100$
Medium
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B$20$
b Rated current through the circuit $i = \frac{{500}}{{100}} = 5\,A$
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Two batteries, one of $emf$ $18\, volts$ and internal resistance $2\,\Omega $ and the other of $emf$ $12\, volt$ and internal resistance $1\,\Omega $, are connected as shown. The voltmeter $V$ will record a reading of .............. $\mathrm{volt}$
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