CAIE A-Level Physics A2 18.1.2 F Qe for the Force on a Charge in an Electric Field Questions

Calculate electric force with F = qE, rearrange the relation for charge or field strength, and interpret signs, direction and units.

Exam points

calculate force on a charge using F = qE
rearrange F = qE to determine charge or field strength and maintain sign and units
interpret the direction of electric force for positive and negative charges in a stated field

[Maximum number: 2]

Two parallel metal plates X and Y are separated by a distance of 0.041 m , as shown in Fig. 6.1.

Fig. 6.1

There is a vacuum between the plates. An electron is at rest at the centre of plate X.
A potential difference (p.d.) of 58 kV is applied across the plates. This causes the electron to accelerate towards plate Y.

Determine the acceleration of the electron.
acceleration = $\mathrm{ms}^{-2}$ [2]

m a=e E
$\begin{aligned} a =\left(1.60 \times 10^{-19} \times 1.41 \times 10^{6}\right) /\left(9.11 \times 10^{-31}\right) =2.5 \times 10^{17} \mathrm{~m} \mathrm{~s}^{-2} \end{aligned}$

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CAIE A-Level Physics A2 18.1.2 F Qe for the Force on a Charge in an Electric Field Questions question 1