Electricity Worksheet-4
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Calculate the potential difference required across a conductor of resistance 5 Ω to make a current of 1.5 A flow through it.
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A torch bulb has 1 Ω resistance. It draws a current of 0.3 A when glowing from a source of 3 V. calculate the resistance of the bulb when glowing and explain the reason for the difference in resistance.
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How much current does an electric heater draw from a 220 V line, if the resistance of the heater (when hot) is 50 Ω?
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How much work is done in moving a charge of 2 C across two points having a potential difference of 12 V?
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An incandescent lamp of resistance 80 Ω draws a current of 0.75 A. Find the line voltage.
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A current of 0.2 A flows through a conductor of resistance 4.5 Ω. Calculate the potential difference at the ends of the conductor.
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A bulb of resistance 400 Ω is connected to 220 V mains. Calculate the magnitude of current.
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An electric heater draws a current of 5 A when connected to 220 V mains. Calculate the resistance of its filament.
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How much current will an electric bulb draw from a 220 V source, if the resistance of the bulb filament is 1200 Ω?
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The potential difference between the terminals of an electric heater is 60 V when it draws a current of 4 A from the source. What current will the heater draw if the potential difference is increased to 120 V?
Answer:
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Resistance of the conductor, R = 5 Ω
Required current, I = 1.5 A
If V is the potential difference required across the conductor, then
V = IR = 1.5 × 5 = 7.5 V
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Potential difference, V = 3 volt
Current through the bulb when glowing, I = 0.3 A
Resistance of the bulb when glowing,
The resistance of the filament of the bulb increases from 1 Ω to 10 Ω (when it becomes hot and glows) because of an increase in its temperature.
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Potential difference, V = 220 V
Resistance of the heater, R = 50 Ω
Using ohm’s law,
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I = V/R = 220/400 = 0.55 A
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R = V/I = 220/5 = 44 Ω
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Resistance of the electric heater,
Changed potential difference V' = 120 V
Changed current, i.e.,
Since R remains the same, by doubling the potential difference, the current is also doubled, i.e., becomes 8 A as I ∝ V.