In the circuit shown in the figure,all the lightbulbs are identical.Which of the following is the correct ranking of the brightness of the bulbs?
A) B and C have equal brightness, and A is the dimmest.
B) A and B have equal brightness, and C is the dimmest.
C) A is brightest, C is dimmest, and B is in between.
D) A is the brightest, and B and C have equal brightness but less than A.
E) All three bulbs have the same brightness.

Question

In the circuit shown in the figure,all the lightbulbs are identical.Which of the following is the correct ranking of the brightness of the bulbs? 
A) B and C have equal brightness, and A is the dimmest. 
B) A and B have equal brightness, and C is the dimmest. 
C) A is brightest, C is dimmest, and B is in between. 
D) A is the brightest, and B and C have equal brightness but less than A. 
E) All three bulbs have the same brightness.

Quizplus · Accepted Answer

In a series circuit, the current remains the same throughout the circuit. Therefore, the bulb with the highest resistance will have the highest voltage drop and consequently the highest brightness. Since all bulbs are identical, they have the same resistance, which means they should have the same brightness. Therefore, options A, B, and C can be ruled out.

Option E is unlikely since there may be some small variations in the bulbs' resistances, and there are some unavoidable losses of electrical energy in the circuit.

Option D is the best choice since A is in series with two bulbs, whereas B and C share the voltage drop from the battery. Thus, A should have higher brightness than B and C. However, since B and C are in parallel, they have the same voltage across them, and therefore they should have equal brightness, but less than A.

In the Circuit Shown in the Figure,all the Lightbulbs Are