Power Question

[FlipDoc2Be]

Sup everyone I don't know why I'm having trouble with this question when it seems easy..

Given a circuit consisting of just a resistor and a battery, if we double the magnitude of the resistor, we then:

A. double the current flowing in the circuit.
B. double the voltage output of the battery.
C. double the power dissipated by the resistor.
D. halve the power dissipated by the resistor.

Using equation P = I^2*R, doesn't it follow that doubling R doubles P? But why is the answer D? Thanks.

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[Econ2MD]

The battery has a fixed or given voltage. Ohm's Law: V=IR. If R is doubled and V is fixed, I is halved. P=IV, so remembering V is fixed, if I is halved then P is halved also.

The other potential answers:
A: From above, current (I) is halved. Wrong.
B: Voltage is fixed in the battery. Adding resistance doesn't change voltage of the power supply. Wrong.
C. From above (P=IV, V fixed) Power is halved not doubled. Wrong.

Hope that helps.

 

[Econ2MD]

It might help to think about a 9V battery. The battery provides a constant 9 volts, right up until just before it dies.

 

[Vanguard23]

Doubling the resistance halves the current, which is a square. That's 1/4th the power. However, doubling the resistance(which is linear) increases the power by two. So overall, it's 1/2th the power.

 

[BerkReviewTeach]

Sup everyone I don't know why I'm having trouble with this question when it seems easy..

Given a circuit consisting of just a resistor and a battery, if we double the magnitude of the resistor, we then:

A. double the current flowing in the circuit.
B. double the voltage output of the battery.
C. double the power dissipated by the resistor.
D. halve the power dissipated by the resistor.

Using equation P = I^2*R, doesn't it follow that doubling R doubles P? But why is the answer D? Thanks.

I'ne noticed you ask about several of the BR inclass questions. Why don't you email your instructor for the detailed solutions to those questions. They aren't given in the handout they give in class, but they are all available on pdf they can email you.

 

[FlipDoc2Be]

I'ne noticed you ask about several of the BR inclass questions. Why don't you email your instructor for the detailed solutions to those questions. They aren't given in the handout they give in class, but they are all available on pdf they can email you.

Hey BerkTeach I actually never took the class but the packets were actually given to me from a student who took the class.

 

[BerkReviewTeach]

Hey BerkTeach I actually never took the class but the packets were actually given to me from a student who took the class.

That would explain it. The passages in those packets will be really useful to you, but the questions and diagrams really won't help you much unless you are in the lecture and going over them with the lecturer. There are several questions where you need something that was written on the board or discussed in order to answer those questions. I wouldn't worry so much about those individual questions unless you are in the actual class. Just focus on the passages in those handouts. The books explain some of the tricks that are shown in the handouts, so if you feel you must go through those questions, hopefully you are reading along in the book as you go through each topic. That will help greatly.