IB Physics SL D 3 6 Force Between Parallel Wires Questions

Calculate force per unit length between parallel current-carrying wires, determine attraction or repulsion, and analyse changing currents and multi-wire systems.

Exam points

calculate magnetic force per unit length between parallel wires using the two currents and their separation
determine whether parallel wires attract or repel from current directions and combine forces from multiple current-carrying wires
analyse force changes with current, distance, wire angle and alternating current, including balance readings and reference-frame evidence

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Study D.3.6—Force between parallel wires conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

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An electrically heated pad is designed to keep a pet warm.

The pad is heated using a resistor that is placed inside the pad. The dimensions of the resistor are shown on the diagram. The resistor has a resistance of $4.2 \Omega$ and a total length of 1.25 m .

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When there is a current in the resistor, the temperature in the pad changes from a room temperature of $20^{\circ} \mathrm{C}$ to its operating temperature at $35^{\circ} \mathrm{C}$ .

(a)

When there is a current in the resistor, magnetic forces act between the resistor strips.

For the part of the resistor labelled RS,

[ 3 ]

(i)

outline the magnetic force acting on it due to the current in PQ .

[ 1 ]

(ii)

state and explain the net magnetic force acting on it due to the currents in PQ and TU .

[ 2 ]

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IB Physics SL D 3 6 Force Between Parallel Wires Questions question 1

Question (a)

Question (i)

Question (ii)