- #1

- 69

- 0

## Homework Statement

In this problem, box A and box B contain unknown combinations of light buls. Bulb 1 is identical to bulb 2. The batteries are ideal.

1. a) In the circuit A (see first attached pic) the voltage across bulb 1 and the voltage across box A are equal. What, if anything can you say about the resistance of box A compared to the resistance of bulb 1. Explain

b) Write an expression for the voltage across the battery, V(Bat), in terms of the voltage readings across box A and across the bulb V(Box A), V (Bulb 1)

2. a) In the circuit B (see second attached pic) the voltage across bulb 2 and the voltage across box B were find to be equal. What, if anything, can you say about the resistance of Box B compared to the resistance of bulb 2?

b) Write an expression for the voltage across the battery V(Bat) in terms of the voltage readings across box B and across the bulb V(Box B) V (Bulb 2)?

3. Box A and box B are now interchanged. It is observed that bulb 2 is now brighter than it was when box B was in that circuit

a). Is the resistance of box A greater than, less than, or equal tot he resistance of box B?

b) Has the current through battery 1 changed? If so, how?

c) Has the current through battery 2 changed? If so how?

## Homework Equations

V = IR

Series: Req = R1 + R2

Parallel: Req = 1/R1 + 1/R2

## The Attempt at a Solution

1. a)Nothing. Without current given, we pretty much cannot tell which resistence is higher.

b) V(Bat) = (V(BoxA)+V(bulb1))/2

2. a) The resistence are the same

b) V(Bat) = B(Box B) + V(Bulb 2)

3. a) Less than. Brighter bulb means more current and less resistence

b) Yes, more current

c) Yes, less current

PS: It seems like I have no problem in determining current and resistence from the given information, but a huge problem in determining voltage. Please provide some clue to this problem. Many thanks~~