IB Physics SL D.3.1 Charge in Electric Fields

Practise determining electric-force direction and acceleration for positive or negative charges and treating perpendicular entry into a uniform field as constant-acceleration…

Exam points

calculate force qE and reverse its direction for a negative charge relative to the field arrow
use a = qE/m with constant-acceleration equations for motion between parallel plates
separate uniform motion parallel to plates from accelerated motion perpendicular to them

[Maximum number: 2]

Two oppositely charged parallel plates are a distance 8.0 cm apart. The potential difference between the plates is 120 V . An alpha particle is placed on the positively charged plate and released from rest. Gravity is ignored.

Figure for Question D.3.1—Charge in electric fields question 1 — IB Physics SL

Show that the acceleration of the alpha particle is about $7 \times 10^{10} \mathrm{~ms}^{-2}$ .

$\begin{aligned} F=<e E=>3.2 \times 10^{-19} \times 1.5 \times 10^{3} \text { OR } 4.8 \times 10^{-16} \mathrm{~N} a=<\frac{F}{m}=>\frac{4.8 \times 10^{-16}}{4 \times 1.67 \times 10^{-27}} \text { OR } 7.2 \times 10^{10} \mathrm{~ms}^{-2} \quad \end{aligned}$

Allow ECF from a).

Award [1] if they use a charge of e and a mass of 2 u obtaining the right result.

[2]

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D.3.1—Charge in electric fields question 1