When the the switch is closed on the circuit shown: When the switch is closed in

Question

When the the switch is closed on the circuit shown:

When the switch is closed in the circuits shown: (a.) Does the lightbulb's brightness increase, decrease or stay the same? Assume the power the dissipated determines brightness. For full points, your answer must include an explanation. (b.) Does the brightness of the single lightbulb in the lower branch of the circuit increase, decrease or stay the same? Assume the power the dissipated determines brightness. (Your answer must include an explanation.)

Explanation / Answer

bright ness increases

let R be the resistance of resistors and r be the resistance of bulb

when the switch is open equivalent resisatnce R1 = R/2 + R = 1.5R

current I1 = V/R1 = V/1.5R

power P1 = I1^2*r

when the switch is closed eqivqlent resistance = R2 = R/3 + R = 1.33R

current I2 = V/R2 = V/1.33R

power = P2 = I2^2*r

R2 < R1

I2 > I1

P2 > P1

++++++++++

b)

decreases

before the switch is closed the resistance R is not present.

after the switch is closed there is some potential drop across the resistor so the potential across the bulbs decreases and the bright ness decreases

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