A) An inductor and a resistor are connected with a double pole switch to a batte

Question

A) An inductor and a resistor are connected with a double pole switch to a battery as shown in the figure. The switch has been in position b for a long period of time.If the switch is thrown from position b to position a (connecting the battery), how much time elapses before the current reaches 176 mA? Answer in units of ms.

B) What is the maximum current in the inductor a long time after the switch is in position a? Answer in units of A.

C) The switch has brushes within it so that the switch can be thrown from a to b without internal sparking. Now the switch is smoothly thrown from a to b, shorting the inductor and resistor. How much time elapses before the current falls to 129 mA? Answer in units of ms

Explanation / Answer

resistamce, R=6.37 ohms,

inductance, L=69 mH

battey potential, V=7v

herem

time constant, T=L/R

T=69*10^-3/(6.37)

T=10.83*10-3 sec

and

maximum current, io=V/R

io=7/6.37

io=1.1 A

now,

a)

current i=176 mA

now,

i=io*(1-e^-t/T)

176*10^-3=1.1*(1-e^-(t/(10.83*10^-3))

t=1.9 msec

b)

maximum current io=1.1 A

c)

current i=129 mA

now,

i=io*(e^-t/T)

129*10^-3=1.1*(e^-(t/(10.83*10^-3))

t=23.21 msec

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