Problem 6: Again from an old exam 12 10 40 +20V 30 set 20 switch A circuit is pu

Question

Problem 6: Again from an old exam 12 10 40 +20V 30 set 20 switch A circuit is put together as shown above. The left voltage source puts out a constant voltage of +20 volts. Part (a) Assume that the switch is open as shown. In this case, what is the value of the current lo through the top of the circuit in the direction show? Give your answer in amps. Hint: You can do this from First Principles, but in this case it might be calculationally a little faster to work out the "Equivalent Resistance" of the network of resistors. Part (b) With the switch open, what is the voltage at point P as measured with respect to the bottom of the left voltage source? Give your answer in volts. Part (c) Suppose we close the switch. What particular value (in volts) Vict is required if we want the current flowing through the 30 Ohm resistor to be zero amps?

Explanation / Answer

a) Io = V/Rnet

= 20/(12 + 10*40/(10+40) + 20)

= 0.5 A

b) voltage across lowr 20 ohms = 0.5*20

= 10 V

so, potential at point P = 10 V

c) 10 V

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