The self inductance of a coil is L. Keeping the length and area same, the number of turns in the coil is increased to four times. The self inductance of the coil will now be 

(1) 14L

(2) L

(3) 4 L

(4) 16 L

Subtopic:  Self - Inductance |
 73%
From NCERT
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A coil has an inductance of 2.5 H and a resistance of 0.5 r. If the coil is suddenly connected across a 6.0 volt battery, then the time required for the current to rise 0.63 of its final value is 

(1) 3.5 sec

(2) 4.0 sec

(3) 4.5 sec

(4) 5.0 sec

Subtopic:  LR circuit |
 58%
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Pure inductance of 3.0 H is connected as shown below. The equivalent inductance of the circuit is

(1) 1 H

(2) 2 H

(3) 3 H

(4) 9 H

Subtopic:  Self - Inductance |
 75%
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If a current of 10 A flows in one second through a coil, and the induced e.m.f. is 10 V, then the self-inductance of the coil is 

(1) 25H

(2) 45H

(3) 54H

(4) 1 H

Subtopic:  Self - Inductance |
 94%
From NCERT
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The adjoining figure shows two bulbs \(B_1\) and \(B_2\) resistor \(R\) and an inductor \(L\). When the switch \(S\) is turned off 

1. Both \(B_1\) and \(B_2\) die out promptly.
2. Both \(B_1\) and \(B_2\) die out with some delay.
3. \(B_1\) dies out promptly but \(B_2\) with some delay.
4.  \(B_2\) dies out promptly but \(B_1\) with some delay.
Subtopic:  Self - Inductance |
From NCERT
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An inductance L and a resistance R are first connected to a battery. After some time the battery is disconnected but L and R remain connected in a closed circuit. Then the current reduces to 37% of its initial value in time ?

(1) RL sec

(2) RLsec

(3) LRsec

(4) 1LRsec

Subtopic:  LR circuit |
 78%
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In an LR-circuit, the time constant is that time in which current grows from zero to the value (where I0 is the steady-state current) 

(1) 0.63 I0

(2) 0.50 I0

(3) 0.37 I0

(4) I0

Subtopic:  LR circuit |
 76%
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In the figure magnetic energy stored in the coil is 

(1) Zero

(2) Infinite

(3) 25 joules

(4) None of the above

Subtopic:  Self - Inductance |
 83%
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The core of a transformer is laminated to reduce energy losses due to  

(1) Eddy currents

(2) Hysteresis

(3) Resistance in winding

(4) None of these

Subtopic:  Transformer |
 82%
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A step-down transformer is connected to 2400 volts line and 80 amperes of current is found to flow in output load. The ratio of the turns in primary and secondary coil is 20 : 1. If transformer efficiency is 100%, then the current flowing in primary coil will be 

(1) 1600 A

(2) 20 A

(3) 4 A

(4) 1.5 A

Subtopic:  Transformer |
 67%
From NCERT
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