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AQA Unit 4 Help

Can someone help me with this question on the January 2010 Section A paper. (Q15).

The answer is B.

For this I used F=EQ, with E being V/d I put d as d/2 giving me E=2V/d and I subbed this into F=EQ to give me F=2VQ/2.

Is the answer B because the field is uniform so the force acting on the charge Q is the same at all points? So E stays as V/d?

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Reply 1

donutellme

Yes exactly! Since it's a uniform field, the force won't change depending on the distance, so all you do is Q*V/d, which gives VQ/d :smile:

Reply 2

particlestudent

Original post by donutellme

Yes exactly! Since it's a uniform field, the force won't change depending on the distance, so all you do is Q*V/d, which gives VQ/d :smile:

Thanks!

Reply 3

particlestudent

Could someone help me with this question...
June 2011-Section B Q2ai

For the first part I used ΔF=kΔL but wrongly substituted 30N/m for k I think. I done 30*60mm which gave me a magnitude of the resultant force on it of 1.8N. This is half of the answer they want and I do not understand what the mark scheme is telling me to do.
It says the resultant force is equal to- (F+ΔF)-(F-ΔF) which gives 2ΔF. I don't understand this.