Direction of a positive charge's velocity in an electric field.

[theBEAST]

Homework Statement

Here is the question with the answer:
http://dl.dropbox.com/u/64325990/phys153Q/21.5.PNG

The Attempt at a Solution

I initially thought it would be A but it isn't and does anyone know why?

 

[tiny-tim]

hi theBEAST!

I initially thought it would be A but it isn't and does anyone know why?

wouldn't it only be A if the electric field was uniform?

 

[theBEAST]

hi theBEAST!


wouldn't it only be A if the electric field was uniform?

Ohhhh thanks that makes sense.

I have another one:
http://dl.dropbox.com/u/64325990/phys153Q/23.9.PNG

I thought this was A, if you put a point charge there... How could it feel a force?

 

[tiny-tim]

what is the equation relating electric potential and electric field?

 

[theBEAST]

what is the equation relating electric potential and electric field?

Hmmmm one is 1/r and one is 1/r^2 so would this mean E ≠ 0? Thus F is not zero? Not really sure.

 

[tiny-tim]

you should know this definition …

the electric field is minus the gradient of the (scalar) potential …

E = -∇φ​

(what did you think the electric potential was for? )

 

[theBEAST]

you should know this definition …

the electric field is minus the gradient of the (scalar) potential …

E = -∇φ​

(what did you think the electric potential was for? )

Thanks Tim, I kind of know the definition... The concept was potential gradients was not taught in our physics class but I did read some of it on my own online. They are related in that the derivative of potential with respect to x is the electric field. So I am not sure how I can relate it to the multiple choice question :S.

I hope I'm not asking too many question at once but it is getting late and I would love to get a hint at what I am doing wrong for this question as well (once I wake up :P):
http://dl.dropbox.com/u/64325990/phys153Q/26.9.PNG

I thought R would affect the maximum charge stored as well because it affects the V of the battery and so the equation C=Q/V?

 

[tiny-tim]

I thought R would affect the maximum charge stored as well because it affects the V of the battery and so the equation C=Q/V?

hint: when the capacitor C is fully charged, what is the voltage drop across the resistor R ?