Physics problems: electricity

Part 5


Problem 41.

A conducting sphere has a net charge of charge. What is the approximate number of excess electrons on the sphere?



Problem 42.

The current passing through a room heater has been halved. What will happen to the heat produced by it?



Problem 43.

An electric iron of resistance 20 ohm draws a current of 5 amperes. Calculate the heat produced in 30 seconds.



Problem 44.

A resistance of 40 ohms and one of 60 ohms are arranged in series across 220 volt supply. Find the heat in joules produced by this combination in half a minute.



Problem 45.

A resistance of 25 ohm is connected to a 12 V battery. Calculate the heat energy in joules generated per minute.





Problem 46.

100 joules of heat is produced per second in a 4 ohm resistor. What is the potential difference across the resistor? 



Problem 47.

An electric iron is connected to the mains power supply of 220 V. When the electric iron is adjusted at minimum heating’ it consumes a power of 360 W but at ‘maximum heating’ it takes a power of 840 W. Calculate the current and resistance in each case.



Problem 48.

Ten bulbs are connected in a series circuit to a power supply line.
Ten identical bulbs are connected in a parallel circuit to an identical power supply line.
1. Which circuit would have the highest voltage across each bulb?
2. In which circuit would the bulbs be brighter?
3. In which circuit, if one bulb blows out, all others will stop glowing?
4. Which circuit would have less current in it?



Problem 49.

Which has a greater resistance, a 100 watt bulb or a 60 watt bulb?



Problem 50.

An electric bulb is rated at 220 V, 100 W. What is its resistance?





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