Namc: PROBLEM4 -8 points In this circuit, the bulbs are identical, with each bul

Question

Namc: PROBLEM4 -8 points In this circuit, the bulbs are identical, with each bulb having a fixed resistance R. [2 points] (a) In terms of R, calculate the equivalent resistance of the circuit when the switch is open. TD [2 points] (b) In terms of R, calculate the equivalent resistance of the circuit when the switch is closed. The battery has a voltage of 15 V. We define the negative terminal of the battery to be at a potential of 0 V, so the positive terminal is at a potential of +15 V. The battery has no internal resistance [1 point] (c) Calculate the potential at point p when the switch is open. [1 point] (d) Calculate the potential at point p when the switch is closed. 2 points] (e) Calculate the voltage across the switch when the switch is open.

Explanation / Answer

(A) B and C are in series,

R1 = R + R = 2 R

now R1 and A are in parallel.

1/R2 = 1/2R + 1/R

R2 = (2/3) R

now R2 and D are in series.

Req = (2/3)R+ R = (5/3) R

(B) C and D in parallel, R1' = 0.5 R

B and R1' in series, R2' = 1.5 R

A and R2' in paralle, Req = 0.6 R

(C) I = 15 / (1.667 R) = 9 / R

Vp = I R = 9 Volt

(D) I = 15 / 0.6 R = 25 / R

Vp = (25/R) (0.5 R) = 12.5 volt

(E) Ic = (9/R) ( R)/(2R + R) = 3/ R

Vswitch = 9 + (3/R)(R) = 12 Volt

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