An inductor and a resistor areconnected with a double pole switch to abattery as

Question

An inductor and a resistor areconnected

with a double pole switch to abattery as

shown in the figure.

The switch has been inposition b fora long

period of time.

5.97

to position a (connecting the battery),how

much time elapses before thecurrent reaches

a long timeafter the switch is in position a?

switch can be thrown from a to b without

internal sparking. Now the switch issmoothly

thrown from a to b,shorting the inductor and

resistor.

An inductor and a resistor areconnected with a double pole switch to abattery as shown in the figure. The switch has been inposition b fora long period of time. 5.97 ohm 1.) If the switch isthrown from position b to position a (connecting the battery),how much time elapses before thecurrent reaches 142 mA? Answer in units of ms. 2.) What is the maximumcurrent in the inductor a long timeafter the switch is in position a? Answer in units ofA. 3.) The switch has brushes within it so thatthe switch can be thrown from a to b without internal sparking. Now the switch issmoothly thrown from a to b,shorting the inductor and resistor.

Explanation / Answer

   a.   Current (rising) inseries LR circuit is          I   =   (V/R)* (1 - e-tR/L)          142 *10-3   =   (7.1 / 5.97) *( 1 - e-t R / L)          ( 1 -e-t R /L)   =   0.119            e-tR /L      =   0.881          t * R /L   =   ln(1/0.881)   =   0.1267          time   t   =   0.1267* 121 * 10-3 /5.97   =   2.57 *10-3   s   =   2.57   ms          b.   Maximumcurrent   I0   =   V/ R   =   7.1 /5.97   =   1.189   A    

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