A solenoid with internal resistance is connected in series with a 20-? resistor

Question

A solenoid with internal resistance is connected in series with a 20-? resistor and a battery of negligible internal resistance and a switch. The above graph shows a voltage measurement as a function time after the switch is closed. (a) Across which circuit element is the voltage being measured? Explain. (You must explain to earn a full credit for this question.) (b) What is the internal resistance of this solenoid? (c) What is the maximum current in this circuit? (d) What is the inductance of this solenoid?

Explanation / Answer

1. voltage is measured for resistance in the circuit. As V =iR suggests the concept of potential drop across resistor in a ckt. the curve clearly indicates the decaying factor or drop of potential which takes place across resisance.

2. change of potential in a time of 8 ms is 50 - 10 = 40 volts

     i = v/R

       = 40/20

   i = 2 amps

3. max current i = v/R = 50/20 = 2.5 amps

4. internal resistance (R+r) = 50/2 =25

r = 25-20 = 5 ohms

4. induced emf v = Ldi/dt

L =40*8*10 0.16 H

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