IB Physics SL D.2.1 Electric Charge Forces

Practise predicting attraction or repulsion between signed charges, drawing equal and opposite force pairs and determining the resultant direction in multi-charge arrangements.

Exam points

state that like charges repel and unlike charges attract along the line joining them
draw equal and opposite forces on the two interacting charges without confusing force and field
add electric-force vectors from several charges to find the net direction or equilibrium point

[Maximum number: 2]

Ion-thrust engines can power spacecraft. In this type of engine, ions are created in a chamber and expelled from the spacecraft. The spacecraft is in outer space when the propulsion system is turned on. The spacecraft starts from rest.

Figure for Question D.2.1—Electric charge forces question 1 — IB Physics SL

The mass of ions ejected each second is $6.6 \times 10^{-6} \mathrm{~kg}$ and the speed of each ion is $5.2 \times 10^{4} \mathrm{~m} \mathrm{~s}^{-1}$ . The initial total mass of the spacecraft and its fuel is 740 kg . Assume that the ions travel away from the spacecraft parallel to its direction of motion.

In practice, the ions leave the spacecraft at a range of angles as shown.

Outline why the ions are likely to spread out.

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D.2.1—Electric charge forces question 1