# Homework Help: Circuits / Switches / Currents -TRUE FALSE QUESTIONS (Pic included)

1. Oct 23, 2011

### niravana21

Circuits / Switches / Currents --TRUE FALSE QUESTIONS (Pic included)

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

I really have no idea, on going about solving this as I don't have my book with me and the homework is due in a few hours. I'm sure if brief explanations are provided with your're reasoning, I will be able to understand the concept.

I realize this is not the way of the physics forum, but I really am desperate right now.

Hope you guys understand. Thanks in advance.

2. Oct 23, 2011

### sandy.bridge

Re: Circuits / Switches / Currents --TRUE FALSE QUESTIONS (Pic included)

A current will develop in the circuit when the switch is closed. After the switch is opened, the same current is within the circuit, however, the total resistance of the circuit has changed.

When you calculate the total initial resistance, is it larger than the resistance if you were to assume the middle branch is an open circuit?

3. Oct 23, 2011

### lewando

Re: Circuits / Switches / Currents --TRUE FALSE QUESTIONS (Pic included)

After the switch is opened, a different current will flow, because the resistance has changed.

4. Oct 23, 2011

### niravana21

Re: Circuits / Switches / Currents --TRUE FALSE QUESTIONS (Pic included)

so if I'm understanding correctly, which I'm not too sure, would it go like this?

8.True
9.False
10.False
11. True
12. True

again, it would be helpful if you can tell me why I'm incorrect rather than provide the right answer. Thanks members!

5. Oct 23, 2011

### lewando

Re: Circuits / Switches / Currents --TRUE FALSE QUESTIONS (Pic included)

If you would like someone to tell you why you are incorrect, you should at least explain why you think you are correct.

6. Oct 23, 2011

### niravana21

Re: Circuits / Switches / Currents --TRUE FALSE QUESTIONS (Pic included)

fair enough :) I don't even know if some of my reasonings are valid haha

8. The total power that is dissipated should be conserved so True
9. (not sure at all, just guessed)
10. Voltage stays the same though out the circuit so False
11. True because closing the switch causes current to flow though and increases resistance?
12. true because uhh it sounds true :) (not sure either way)

7. Oct 23, 2011

### lewando

Re: Circuits / Switches / Currents --TRUE FALSE QUESTIONS (Pic included)

Sorry, this is not so. Energy may be conserved, power is another animal. The resistive load on the voltage supply changes, therefore the current changes. What is the equivalent resistance before the switch is opened? After it is opened? Assume the battery is 1.5V. What is the current (provided by the battery) before and after switch is opened? Use P=VI, P=VI, P=V2/R or P=I2R to compare power dissipated in each circuit.

After the switch is opened R2 is just dangling out there--how can current go through it?
When you figure out what the currents are (before/after switch opened) you will be able to answer this.
When you figure out the equivalent resistance of the circuits (before/after switch opened) you will be able to answer this.
When you figure out the current of circuits (before/after switch opened) you will be able to answer this.