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# OCR A Phy 4 Question - Field Strengths watch

1. i been given a diagram of a field. using it i can determine the voltage at a point and the distance between two charges. from this i can deduce the force. i then get asked to work out the magnitude and direction of an electron experiencing the force at this point. my minds gone to pot, how do i do it?
2. (Original post by El Chueco)
i been given a diagram of a field. using it i can determine the voltage at a point and the distance between two charges. from this i can deduce the force. i then get asked to work out the magnitude and direction of an electron experiencing the force at this point. my minds gone to pot, how do i do it?
You can work out the voltage using the formula E = V/d (V = Ed)
You can work out the force on the electron using E = F/Q
Hope this is of some use
3. (Original post by josklkr)
You can work out the voltage using the formula E = V/d (V = Ed)
You can work out the force on the electron using E = F/Q
Hope this is of some use
FEQ! i knew there was a reason thse questions made me swear... thanks dude.
4. (Original post by El Chueco)
FEQ! i knew there was a reason thse questions made me swear... thanks dude.
Please i could help
5. (Original post by josklkr)
You can work out the voltage using the formula E = V/d (V = Ed)
You can work out the force on the electron using E = F/Q
Hope this is of some use
Im not sure you can do that. That formula is for capacitors where you assume a uniform field - that isnt the case here. Maybe you can get away with it at A level but Id do it like this:

V = Q/4piEor ---> rearrange to find Q

bang Q into:

F = Q1Q2/4piEor^2

Edit: just to clarify do we have 2 charges and then an electron or is an electron 1 of the 2 charges. My method works if its 1 of the 2 charges otherwise you would need a superposition
6. (Original post by El Chueco)
i been given a diagram of a field. using it i can determine the voltage at a point and the distance between two charges. from this i can deduce the force. i then get asked to work out the magnitude and direction of an electron experiencing the force at this point. my minds gone to pot, how do i do it?
if they are point charges use the eqtns:

F= Q1xQ2 / r^2 (if you know the two charges)

and E=F/Q1 (if you know the fieldstrengh and one charge)

Don't think you can use E=V/d, unless its a uniform field

pk

P.S. "FEQ" - what a lame joke

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