IB Physics SL A 2 14 Electric Force Fe Questions

Practise the IB Physics SL A.2.14 definition of electric force as the force exerted by an electric field on a small positive test charge.

Exam points

Identify electric force Fe as the force acting between charged bodies in an electric field.
Determine electric-force magnitude and direction from charge, field or interaction evidence using complete mark-scheme support.

[Maximum number: 3]

A vertical wall carries a uniform positive charge on its surface. This produces a uniform horizontal electric field perpendicular to the wall. A small, positively-charged ball is suspended in equilibrium from the vertical wall by a thread of negligible mass.

Figure for Question IB Physics SL A 2 14 Electric Force Fe Questions question 1 — IB Physics SL

The thread makes an angle of $30^{\circ}$ with the vertical wall. The ball has a mass of 0.025 kg .

Determine the horizontal force that acts on the ball.

Horizontal force on ball $F=T\sin30^\circ$ .
$T=mg/\cos30^\circ$ .
$F=mg\tan30^\circ=0.025\times9.8\times\tan30^\circ=0.14\ \mathrm{N}$ .

Allow $g=10\ \mathrm{N\ kg^{-1}}$ . Award [3] for a bald correct answer. Award [1 max] for an answer of zero, interpreting the horizontal force as the horizontal component of the net force.

F=mg\tan30^\circ=0.025\times9.8\times\tan30^\circ=0.14\ \mathrm{N}

All question bank results loaded

IB Physics SL A 2 14 Electric Force Fe Questions question 1