2049_ch27B

2049_ch27B - Circuits The light bulbs in the circuits below...

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PHY2049: Chapter 27 31 Circuits Î The light bulbs in the circuits below are identical. Which configuration produces more light? ± (a) circuit I ± (b) circuit II ± (c) both the same Circuit II has ½ current of each branch of circuit I, so each bulb is ¼ as bright. The total power in circuit I is thus 4x that of circuit II.

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PHY2049: Chapter 27 32 Circuits Î The three light bulbs in the circuit are identical. What is the brightness of bulb B compared to bulb A? ± a) 4 times as much ± b) twice as much ± c) the same ± d) half as much ± e) 1/4 as much Use P = I 2 R. Thus 2x current in A means it is 4x brighter.
PHY2049: Chapter 27 33 Circuit Problem (1) Î The light bulbs in the circuit are identical. What happens when the switch is closed? ± a) both bulbs go out ± b) the intensity of both bulbs increases ± c) the intensity of both bulbs decreases ± d) nothing changes Before switch closed: V a = 12V because of battery. V b =12 because equal resistance divides 24V in half. After switch closed: Nothing changes since (a) and (b) are still at same potential. (a) (b)

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PHY2049: Chapter 27 34 Circuit Problem (2) Î The light bulbs in the circuit shown below are identical. When the switch is closed, what happens to the intensity of the light bulbs? ± a) bulb A increases ± b) bulb A decreases ± c) bulb B increases ± d) bulb B decreases ± e) nothing changes (b) (a) Before switch closed: V a = 12V because of battery. V b =12 because equal resistance divides 24V in half. After switch closed: Nothing changes since (a) and (b) are still at same potential.
PHY2049: Chapter 27 35 (a) (b) Circuit Problem (3) Î The bulbs A and B have the same R. What happens when the switch is closed? ± a) nothing happens ± b) A gets brighter, B dimmer ± c) B gets brighter, A dimmer ± d) both go out Before: V a = 24, V b = 18. Bulb A and bulb B both have 18V across them.

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2049_ch27B - Circuits The light bulbs in the circuits below...

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