1.

An inductor (L=0.03H) and a resistor (R=0.15kOmega) are connected in series to a battery of 15 V emf in a circuit shown below. The key K_1 has been kept closed for a long time. Then at t=0 , K_1 is opened and key K_2 is closed simulatenously. At t=1 ms, the current in the circuit will be (e^5cong150)

Answer»

100 mA
67 mA
6.7mA
0.67 mA

Solution :When the KEY`K_1` is closed , CURRENT through the inductor,
`I_0=e/R=15/(0.15times10^3)=0.1A`
Here, t=1 ms =`10^-3` s
Time CONSTANT of the LR circuit,
`t_0=L/R=0.03/(0.15times10^3)=2times10^-4s`
`thereforet/t_0=10^-3/(2times10^-4)=5`
`thereforeI=I_0e^(-t//t_0)=0.1e^-5=0.1/150=0.67times10^-3A`
=0.67 mA


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