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Urgent electricity question


m.k.2015

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Hello everyone, 

can someone please help me by explaining the attached question. The answer is there, but I don't know how they got it 

Thankkkks 

 

First of all, the solution in the picture that you posted is wrong due to typing error (i suppose) because gif.latex?\frac{8.0\times 10^{-3} \: J}{ and not gif.latex?-1\times 10^{2}. Apart from this typing error which leads to the wrong final answer, their method of solving is completely correct

 

 

If you find this solution hard to understand, I suggest you use conservation of energy to solve this problem:

  1. At point 'a', the total energy of the particle is gif.latex? E + qV_a, where gif.latex?E is the external energy, and gif.latex?V_a is the potential at point 'a'
  2. At point 'b', the total energy of particle has now become gif.latex? E_k + qV_b, where gif.latex? E_k is the kinetic energy of the particle, and gif.latex?V_b is the potential at point 'b'
  3. Now, from conservation of energy we have: gif.latex? E+qV_a = E_k + qV_b. Thus gif.latex? E-E_k = q(V_b - V_a)
  4. Plug in the given values, we have: gif.latex? \varDelta V = \left|V_b - V_a which is also the right answer

If there's anything unclear, feel free to ask

Edited by Vioh
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