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Leaving Cert Physics: The motor effect

How often The motor effect comes up on the Physics papers, every year it was asked, and questions to try.

HL Asked on 8 of the last 10 Higher Level papers, most recently in 2026. most years

OL Asked on 3 of the last 10 Ordinary Level papers, most recently in 2023.

June 2027 is the first exam on the new Physics course. These come from the 2016–2026 papers, so read them as a guide.

The motor effect, Higher Level(7 marks)

Quick ones on The motor effect.

(a)Formula for the force on a current-carrying conductor at right angles to a magnetic field?
  1. F = B/Il
  2. F = BIl
  3. F = BIl²
(b)Force on a 0.50 m length of wire carrying 4.0 A at right angles to a field of 0.20 T?
  1. 0.10 N
  2. 4.0 N
  3. 0.40 N
(c)Which rule gives the direction of the force on a current-carrying conductor in a magnetic field?
  1. Fleming's left-hand rule
  2. Lenz's law
  3. Fleming's right-hand rule
Show the answers

(a) F = BIl

(b) 0.40 N

(c) Fleming's left-hand rule

Your turn: Higher Level questions on The motor effect.

Higher Level

Asked on 8 of the last 10 Higher Level papers, most recently in 2026. most years

Every paper, year by year

YearWhere it came up
2026Q11
2025Q13
2024Q8
2023Q6(j), Q13
2022Q6(h)
2021Q10
2019Q9
2018Not asked
2017Q11
2016Not asked

Links open the State Examinations Commission’s paper for that year.

More The motor effect questions

The motor effect, 2 marks

What does the split-ring commutator do in a DC motor?

  1. Increases the voltage across the coil every half turn so it turns faster
  2. Changes the alternating current from the supply into a direct current for the coil
  3. Reverses the current in the coil every half turn so it keeps turning the same way
Show the answer

Reverses the current in the coil every half turn so it keeps turning the same way

Without it the force on each side of the coil would reverse after half a turn and the coil would just rock. Brushes press on the split ring.

The motor effect, 2 marks

A current-carrying wire lies parallel to a magnetic field. What is the force on it?

  1. Half the maximum force
  2. Zero
  3. The maximum possible force
Show the answer

Zero

The motor effect force depends on the part of the field at right angles to the current. Parallel to the field there is none, so F = 0.

The motor effect, 2 marks

How can the direction of rotation of a simple dc motor be reversed?

  1. Swap the connections to the power supply
  2. Double the current flowing in the coil
  3. Put more turns of wire on the coil
Show the answer

Swap the connections to the power supply

Reversing the current (or the magnetic field) reverses the force on each side of the coil (Fleming's left-hand rule). More current or turns only make it faster.

Ordinary Level

Asked on 3 of the last 10 Ordinary Level papers, most recently in 2023.

Every paper, year by year

YearWhere it came up
2026Not asked
2025Not asked
2024Not asked
2023Q14(d)
2022Not asked
2021Q14(c)
2019Not asked
2018Not asked
2017Q9
2016Not asked

Links open the State Examinations Commission’s paper for that year.

More The motor effect questions

The motor effect, 2 marks

Which device uses the force on a current-carrying conductor in a magnetic field?

  1. A transformer
  2. A generator
  3. An electric motor
Show the answer

An electric motor

In a motor the forces on the coil turn it round. A generator does the reverse: motion produces a current by induction.

The motor effect, 2 marks

How can the direction of the force on a current-carrying wire in a magnetic field be reversed?

  1. Use a thicker wire of the same metal
  2. Reverse the direction of the current
  3. Increase the size of the current
Show the answer

Reverse the direction of the current

Reversing the current or the magnetic field reverses the force. A larger current only makes the force bigger.

The motor effect, 2 marks

What makes the coil of a DC motor turn?

  1. The force on the current-carrying coil in a magnetic field
  2. Heat from the current makes the coil expand and turn
  3. Static charge on the coil is repelled by the magnet's poles
Show the answer

The force on the current-carrying coil in a magnetic field

Current in the coil in the magnet's field feels a force (the motor effect). Forces on opposite sides act in opposite directions and turn the coil.

Other Physics topics

All of Leaving Cert Physics