A circuit contains 3 identical light bulbs, A,B, and C, as shown. A switch allow

Question

A circuit contains 3 identical light bulbs, A,B, and C, as shown. A switch allows a portion of the circuit to be closed or open. Determine how the brightness of the light bulbs change after the switch is closed.

A. Assume the battery has a potential V=12V, and each bulb has a constant resstance R=50 ohm. Find the power output of each bulb, Ba, Bb, and Bc while the switch is open.

B.Find the power output of each bulb while the switch is closed.

C. How does the birghtness in each bulb change as the switch is closed?

A, B, and C, as shown be "closed" or "open". Bulbs change after the v = 12V, and bulb Find the power output of each bulb, P = (v/R)

Explanation / Answer

a)

When switch is open ,equivalent resistance is

Req =Ra+Rb=50+50

Req=100 ohms

,the current in the circuit is

I=V/Req =12/100

I=0.12 A

so power consumed by

Bulb A

Pa=I^2*Ra =0.12^2*50

Pa=0.72 W

Bulb B

Pb=I^2*Rb

Pb=0.72 W

BulB C

Pc=0 W

b)

b)

When switch is closed ,equivalent resistance

Req =Ra+(Rb*Rc/Rb+Rc) =50+(50*50/50+50)

Req =75 ohms

Current in the circuit

I=V/Req =12/75

I=0.16 A

BulB A

Pa=I^2*R=0.16^2*50

Pa=1.28 W

Voltage across bulb B and C by voltage divider rule

Vbc =V*(Rbc/Ra+Rbc) =12*(25/25+50)

Vbc =4 V

BulB B

Pb=Vbc^2/Rb =4^2/50

Pb=0.32 W

Bulb C

Pc=Vbc^2/Rc =4^2/50

Pc=0.32 W

b)

so after switch is closed ,Bulbs A glows more brightly then Bulb B and Bulb C, Bulb B and Bulb C glow with equal brightness

,

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