標題:
al phy 97 mc 28
發問:
97 mc 28a charged particle is accelerated across the gap between two parallel metal plates maintained at a certain potential difference in a vacuum. assuming ther is no gravitational force , the energy acquired by the charged particle in crossing the gap depends on 1) the mass of the charged... 顯示更多 97 mc 28 a charged particle is accelerated across the gap between two parallel metal plates maintained at a certain potential difference in a vacuum. assuming ther is no gravitational force , the energy acquired by the charged particle in crossing the gap depends on 1) the mass of the charged particle 2) the width of the gap 3) the potential difference between the plates. A. (1)ONLY B. (3)ONLY C. (1)AND(2)ONLY D. (2)AND (3)ONLY E. ALL ANS: B WHY ? I think the ans (2) correct we have that equation E=V/d => electric field = potential difference / separation between two plates U=qV => qEd potential energy = charge * potential difference i know that Fd= qV since E=V/d but why that is wrong U=qV => qEd
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最佳解答:
The answer is B. 3 only. Assuming the potential difference between the two plates is V. So, energy required to cross the gap, U = qV where q is the magnitude of charge on the charged particle. So, it depends on the p.d. between the two plates. For (1), it is not true since U = qV, which is independent of the mass of the particle. As long as the particle has a certain number of charge, it will have a certain energy. For (2), although we can write qV = qEd, where d is the width of the gap. However, the p.d. across the two plates is kept a constant. So, by V = Ed, when V is kept constant, d decreases, E will increase, and vice versa. So, it does not depend on the width of the gap. It is because if varying the distance, the electric field strength will also change.
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