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# http://filestore.aqa.org.uk/subjects/AQA-PHYA41-QP-JUN15.PDF Watch

1. not sure where to start on question 15 ?
2. The answer is A. It is held stationary in avertical electric field. If there wasn't an electric field, then the positive ion would be under the effect of gravity and would fall downwards. So as it is stationary we can see that the force from the field is the same as the weight but acting upwards. So firstly we now know its acting upwards, so we have answers A and C left (could just then guess from here 50% chance). Then use the formula E = F/Q and substitute mg for F (F=mg). We know the charge-mass ratio so rearrange E=mg/Q to get a Q/m so we can substitute 2.40 × 10^7 C kg–1. So we rearrange and get E = g / (Q/M) and so E= 9.81/ (2.40 × 10^7) which equals 4.09x10^-7 (so A).

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Updated: May 15, 2016
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