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Some questions after going through test papers (EDEXCEL) watch

1. 1) Finding whether a quantity is vector or not. I was met a question to decide which one is a vector quantity: electric field strength, magnetic flux density, momentum or potential difference.

I approached this question first by going through their equations, so electric field strength = F/C, and force is a vector quantity so no. Momentum = mass x velocity, and velocity is a vector quantity so no.

I did not remember what the magnetic flux density equation was, but I know magnetic flux density has a direction because of the left hand rule business.. but at the same time I thought potential difference (voltage) is a vector quantity too for some reason, because of volt travels in a direction? It is carried by current in a direction.. I had to choose voltage in the end (which was right), but how can I approach questions like this better? How come potential difference is not a vector?

2) In the alpha scattering experiment, what does kinetic energy/velocity given to the alpha particles have to be the same? What does it have to do with how far they are deflected or whatever
2. If you're thinking about voltage traveling you're probably not thinking about it correctly. current is the flow, voltage is the "pressure". one volt is one Joule per coulomb and energy is not a vector. Potential difference is always just a scalar number - you talk about the potential difference between point A and point B being a number of volts in a similar way to how you might talk about the gravitational potential energy difference difference between a kg at the top of a hill and a kg the bottom of a valley.
3. In reply to the second question I think that giving them the same Kinetic Energy/Velocity means that they all have the same momentum at the point of impact. If some of them have a high momentum than others, if they hit the exact same point, they wont have the same deflection. Ones with less velocity gets repelled more. Im guessing this is like a 1 marker?
4. Yeah potential difference is the work done per unit charge.

Or in mathematical terms:
Potential Difference between two points to be given by,

This definition of Potential Difference between points A and B does not say anything about the actual value VA and VB so we can apply an arbitrary offset to each without effecting any results. It is conventional to define a point at ∞ having a Potential of zero, so V∞=0, so the Potential of a point A is given by
where W∞A is the work done by an external agent to take a charge q0 from infinity to the point A. Using the definition of W we therefore have that,

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Updated: December 28, 2014
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