4.5.4Electricity and Magnetism
Force ON A Current-carrying Conductor — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions
5 min read 8 parts Lesson 56 of 65 1 quiz
Lesson summary
4.5.4 Force on a Current-Carrying Conductor — IGCSE PHYSICS notes: Describe the force on a current-carrying conductor in a magnetic field, the factors affecting it and Fleming's left-hand rule.Force — a current-carrying conductor in a magnetic field experiences a force, because t…
- Perpendicular
- Demonstration
- Reversing the current
- Reversing the field
- Larger current
- Stronger magnetic field
Part 1 of 6The motor effect
Force
- Force a current-carrying conductor in a magnetic field experiences a force, because the wire's own field interacts with the external field.
Perpendicular
- Perpendicular the force acts only if the current is perpendicular to the field, and it is zero if the current is parallel to the field.
Demonstration
- Demonstration a copper or aluminium rod on two rails between the poles of a magnet moves when current passes through it.
Part 2 of 6Factors affecting the force
Reversing the current
- Reversing the current reverses the direction of the force.
Reversing the field
- Reversing the field reverses the direction of the force.
- Reversing both leaves the force unchanged.
Larger current
- Larger current a bigger force.
Stronger magnetic field
- Stronger magnetic field a bigger force.
Longer wire in the field
- Longer wire in the field a bigger force.
Part 3 of 6Fleming's left-hand rule (Extended)
1First finger
- First finger the direction of the magnetic field, from N to S.
2Second finger
- Second finger the direction of the current, from positive to negative.
3Thumb
- Thumb the direction of the force (thrust) and the movement.
4Perpendicular
- Perpendicular all three are at right angles to each other.
5Hand
- Hand use the left hand.
1
Find the field direction, N to S.
2
Find the conventional current direction, + to −.
3
Hold the thumb, first and second fingers at right angles.
4
Point the first finger along the field and the second along the current.
5
Read the force direction from the thumb.
Part 4 of 6Charged particles in a magnetic field (Extended)
Charged particles in a magnetic field (Extended)
Beam as current
- Beam as current a beam of charged particles is a current, so it is deflected by a magnetic field.
Force
- Force it is at right angles to both the velocity and the field.
Electrons
- Electrons point the second finger opposite to the electron velocity, since conventional current is opposite to electron flow.
Angle
- Angle a particle moving perpendicular to the field feels the maximum force, one moving parallel feels none and one at an angle feels a smaller force.
Path
- Path the force is always perpendicular to the motion, so a particle moves along a circular arc and its speed is unchanged.
Part 5 of 6Uses
Electric motors
- Electric motors a coil in a field turns.
Loudspeakers
- Loudspeakers a coil in the field of a permanent magnet vibrates the cone.
Moving-coil meters.
Part 6 of 6More from the specification
1
Lorentz force and motor power
- Lorentz force and motor power magnetic forces acting perpendicular to current flow spin armature coils, generating useful mechanical output power.
2
Force on a conductor
- Force on a conductor a current-carrying wire in a magnetic field feels a force at right angles to both field and current, given by Fleming's left-hand rule.
3
Factors affecting force
- Factors affecting force the force increases with larger current, stronger field and longer wire in the field.
4
Solenoid
- Solenoid a coil that produces a field like a bar magnet, strengthened by more turns or a soft iron core.
5
Electromagnetic induction link
- Electromagnetic induction link moving a wire in a field induces a voltage,
- and a transformer uses a changing field between primary and secondary coils.
6
Force on a conductor
- Force on a conductor a current-carrying wire in a magnetic field feels a force at right angles to both field and current, given by Fleming's left-hand rule.
7
Factors affecting force
- Factors affecting force the force increases with larger current, stronger field and longer wire in the field.
8
Solenoid
- Solenoid a coil that produces a field like a bar magnet, strengthened by more turns or a soft iron core.
9
Electromagnetic induction link
- Electromagnetic induction link moving a wire in a field induces a voltage,
- and a transformer uses a changing field between primary and secondary coils.
10
Generator
- Device that turns kinetic energy into electrical energy.
11
Brushes
- Carbon contacts pressing on the slip rings.
12
Field lines
- Lines showing the direction and strength of a magnetic field.
13
Induced magnet
- Material temporarily magnetised in a magnetic field
14
Potential difference
- Work done by a unit charge passing through a component.
15
Step-up transformer
- Transformer with more turns on the secondary, raising the voltage.
16
Step-down transformer
- Transformer with fewer turns on the secondary, lowering the voltage.
17
Electromagnetic induction
- Production of an e.m.f. by relative movement of a conductor and a magnetic field.
18
IpVp
IsVs
What the symbols mean: V = voltage (V) · N = number of turns · I = current (A) · p = primary coil · s = secondary coil
19
Transformer
- Device that changes the size of an alternating voltage.
20
Primary
- Input coil.
21
Solenoid
- Long coil of wire carrying a current
22
Voltmeter
- Instrument that measures p.d., connected in parallel.
Key terms
| Term | Meaning |
|---|---|
| Motor effect | Force on a current-carrying conductor in a magnetic field. |
| Fleming's left-hand rule | Rule giving the direction of force, field and current. |
| Thrust | The force on the conductor. |
| Magnetic field | Region in which a magnetic pole experiences a force. |
| Perpendicular | At right angles. |
Avoid these mistakes
1
Using the right hand for the motor rule — it is the left hand.
2
Forgetting that there is no force when the current is parallel to the field.
3
Pointing the second finger along electron flow — it must follow conventional current.
4
Thinking that reversing both the current and the field reverses the force.
Marked practiceQuizzes for this lesson
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