Electrostatics Multiple Choice Questions

[bap902]

I bolded the answer I think is correct - I'm just a little unsure on these, any help would be appreciated!

1. A capacitor and resistor are connected in a series with a batter and a switch. The instant after the switch is closed

A. the voltage across the resistor is equal to the emf of the battery
B. the voltage across the capacitor is equal to the emf of the battery
C. the voltage across the resistor is equal to zero
D. the current is equal to zero
E. both A and B are correct

2. The figure below shows a set of equipotential lines. The electric field has the greatest magnitude at point

http://img136.imageshack.us/img136/623/diagram1ks6.png

A. A
B. B
C. C
D. D
E. E

3. Four charges are arranged on the corners of a square as shown below:

http://img126.imageshack.us/img126/1994/diagram2zb7.png

At which point (or points) is the electric field equal to zero?

A. B and E
B. D and A
C. A and C
D. A and B
E. E only

 

[Vuldoraq]

Please can you explain your reasoning as to how you came to your answers?

 

[bap902]

For question #1, I chose that the voltage across the resistor is equal to the EMF of the battery because the EMF of the battery directly relates to the voltage of electrical energy. It is the voltage that is connected with the behavior of the resistance and the capacitor.

For #2, I read online that the electric field has the greatest magnitude at the point closest to the source. The magnitude decreases as the distance from a location to the source increases. I chose C, because it is closest to the smallest equipotential line, which I figured was the initial source.

I chose D and A for question #3 because if the charges are of equal magnitude, then the field is zero halfway between them.

 

[Vuldoraq]

For question #1, I chose that the voltage across the resistor is equal to the EMF of the battery because the EMF of the battery directly relates to the voltage of electrical energy. It is the voltage that is connected with the behavior of the resistance and the capacitor.

Correct, although as the capacitor charges the voltage across the resistor will decrese.

For #2, I read online that the electric field has the greatest magnitude at the point closest to the source. The magnitude decreases as the distance from a location to the source increases. I chose C, because it is closest to the smallest equipotential line, which I figured was the initial source.

I think this is right.

I chose D and A for question #3 because if the charges are of equal magnitude, then the field is zero halfway between them.

This is definitely wrong. If you placed a charge at either of these points it would certianly move. See the below sight, set up your charges and look at the field lines. You want a region with no filed lines going through it.

http://www.its.caltech.edu/~phys1/java/phys1/EField/EField.html

 

[bap902]

Thanks! I couldn't get the site to work on my internet for some reason (nothing would load) so any additional help on #3 would be appreciated.