Bulbs and Switches 6
The switch is closed. Bulb B gets dimmer. Compare the power before and after, assuming constant resistance for all bulbs.
The switch is closed. Bulb B gets dimmer. Compare the power before and after, assuming constant resistance for all bulbs.
A) Power after is 1/3 power before
A) Power after is 1/3 power before
B) Power after is 2/3 power before
B) Power after is 2/3 power before
C) Power after is 1/2 power before
C) Power after is 1/2 power before
D) Power after is 1/4 power before
D) Power after is 1/4 power before
E) Other
E) Other
Solution: E. It was previously shown that the current through B before is (1/2)*emf/R and the current through B after is (1/3)*emf/R. So the current is 2/3 what it was before. Since power is proportional to the current squared (P = I^2*R), the power is now 4/9 what is was before.
Solution: E. It was previously shown that the current through B before is (1/2)*emf/R and the current through B after is (1/3)*emf/R. So the current is 2/3 what it was before. Since power is proportional to the current squared (P = I^2*R), the power is now 4/9 what is was before.
