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Some questions after going through test papers (EDEXCEL) Watch

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    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
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    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.
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    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?
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    Yeah potential difference is the work done per unit charge.


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


     \Delta V = V_B − V_A = \frac {W_AB}{q_0}


    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               V_A =  \frac {W_A\infty}{q_0}
    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,  V_A = −\int^A_\infty \ \frac {1}{q_0} \vec{F} . d \vec{r}
 
 
 
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