Physics 9702 · AS & A Level · Potential difference and power

Potential difference and power — practice question

Placed in a vacuum, two vertical metal plates are $0.12\,\text{m}$ apart, and each plate is $2.0\,\text{m}$ long. The potential difference across the plates is $900\,\text{V}$. The electric field between the plates is uniform. A negatively charged sand particle is let go from rest at point X, which lies $0.080\,\text{m}$ horizontally from the top of the positively charged plate. The particle then moves in a straight line and strikes the positively charged plate at its lowest point Y, as shown in Fig. 4.1.
(a)[2]

Describe how the field lines (lines of force) are arranged between the plates.

(b)[1]

State the names of the two forces acting on the particle during its motion from X to Y.

(c)[2]

By considering the vertical motion of the sand particle, show that the time taken for the particle to move from X to Y is $0.64\,\text{s}$.

(d)[2]

Calculate the horizontal component of the particle's acceleration.

(e(i))[2]

Calculate the magnitude of the electric field strength.

(e(ii))[2]

The sand particle has mass $m$ and charge $q$. Use your answers in (d) and (e)(i) to determine the ratio $\frac{q}{m}$.

(f(i))[1]

Another particle has a smaller magnitude of the ratio $\frac{q}{m}$ than the sand particle. This particle is also released from point X. For the motion of this particle, state the effect, if any, of the smaller magnitude of the ratio on the vertical component of the acceleration.

(f(ii))[1]

For the motion of this particle, state the effect, if any, of the smaller magnitude of the ratio on the horizontal component of the acceleration.

Worked solution & mark scheme

This 13-mark question has a full step-by-step worked solution and mark scheme. One marking point: “straight (horizontal) lines from the $+0.90\,\text{kV}$ plate to the $0\,\text{V}$ plate” …

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