The resistance of hot tungsten filament is about 10 times the cold resistance. What will be the resistance of 100 W and 200 V lamp when not in use?
When the filament is hot,
Hence, when cold, the resistance is 40 .
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The resistance of hot tungsten filament is about 10 times the cold resistance. What will be the resistance of 100 W and 200 V lamp when not in use?
When the filament is hot,
Hence, when cold, the resistance is 40 .
Two electric bulbs A and B are rated 60 W and 100 W, respectively. If they are connected in parallel to the same source, then,
Given . We know that current flowing through the bulb is I = P/V. We also know that as both the bulbs are connected in parallel, potential difference (V) across both the bulbs is the same. Thus, . Since the power of bulb B is greater than that of bulb A, bulb B draws more current than bulb A.
A factory is served by a 220 V supply line. In a circuit protected by a fuse marked 10 A, the maximum number of 100 W lamps in parallel that can be turned on is :
The current required by each bulb is :
If n bulbs are joined in parallel, then,
.
A 100 W bulb designed to operate on 100 V is to be connected across a 500 V source. Find the resistance to be put in series so that bulb consumes 100 W only.
The resistance of an ideal voltmeter is
The resistance of an ideal voltmeter is considered as infinite.
The net resistance of a voltmeter should be large to ensure that :
The resistance of voltmeter is too high, so that it draws negligible current from the circuit, hence potential drop in the external circuit is also negligible.
A voltmeter of resistance 1000 Ω gives full-scale deflection when a current of 100 mA flow through it. The shunt resistance required across it to enable it to be used as an ammeter reading 1 A at full-scale deflection is :
By using
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A galvanometer has 30 divisions and a sensitivity 16 It can be converted into a voltmeter to read 3 V by connecting (approximately):
In a circuit, 5 percent of total current passes through a galvanometer. If the resistance of the galvanometer is G then the value of the shunt is :
⇒
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A voltmeter has a range 0-V with a series resistance R. With a series resistance 2R, the range is 0-V'. The correct relation between V and V' is :
For conversion of galvanometer (of resistances) into voltmeter, a resistance R is connected in series.
∴ and
⇒ ⇒
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