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The motor effect
This topic links current-carrying conductors to magnetic fields and forces, including HT motor-effect calculations and physics-only electromagnetic devices.
35
Objectives
175
Flashcards
175
Questions
90 min
Study time
AQAGCSEPhysicsMagnetism and electromagnetism
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Syllabus checklist
What you need to know
35 objective pages available
Electromagnetism15 objectives
- State that when a current flows through a conducting wire a magnetic field is produced around the wire.
- Describe how the strength of the magnetic field around a wire depends on current through the wire.
- Describe how the strength of the magnetic field around a wire depends on distance from the wire.
- Describe how shaping a wire to form a solenoid increases the strength of the magnetic field created by a current.
- State that the magnetic field inside a solenoid is strong and uniform.
- Describe the magnetic field around a solenoid as having a similar shape to that of a bar magnet.
- State that adding an iron core increases the strength of the magnetic field of a solenoid.
- Define an electromagnet as a solenoid with an iron core.
- Describe how the magnetic effect of a current can be demonstrated.
- Draw the magnetic field pattern for a straight wire carrying a current.
- Draw the magnetic field pattern for a solenoid, showing the direction of the field.
- Explain how a solenoid arrangement can increase the magnetic effect of the current.
- Apply WS 2.2 when drawing magnetic field patterns for a current-carrying wire and solenoid.
- (Physics only) Interpret diagrams of electromagnetic devices in order to explain how they work.
- (Physics only) Apply WS 1.4 when explaining electromagnetic devices from diagrams.
Fleming's left-hand rule (HT only)10 objectives
- (HT only) Describe the motor effect as the force on a current-carrying conductor placed in a magnetic field.
- (HT only) State that the magnet producing the field and the conductor exert a force on each other.
- (HT only) Use Fleming's left-hand rule to represent the relative orientation of force, current and magnetic field.
- (HT only) Recall the factors that affect the size of the force on a current-carrying conductor.
- (HT only) Recall that the force depends on magnetic flux density, current and length of conductor in the field when the conductor is at right angles to the field.
- (HT only) Recall and apply the equation F = B x I x l for a conductor at right angles to a magnetic field.
- (HT only) Identify force F in newtons, magnetic flux density B in tesla, current I in amperes and length l in metres.
- (HT only) Rearrange F = B x I x l to calculate magnetic flux density, current or length where appropriate.
- (HT only) Apply MS 3b and MS 3c when using the motor-effect equation.
- (HT only) Recognise that the motor-effect equation is given on the Physics equation sheet.
Electric motors (HT only)5 objectives
- (HT only) State that a coil of wire carrying a current in a magnetic field tends to rotate.
- (HT only) Describe rotation of a current-carrying coil in a magnetic field as the basis of an electric motor.
- (HT only) Explain how the force on a conductor in a magnetic field causes rotation of the coil in an electric motor.
- (HT only) Link opposite forces on the sides of a current-carrying coil to the turning effect in an electric motor.
- (HT only) Use motor-effect reasoning to explain the operation of a simple electric motor.
Loudspeakers (physics only) (HT only)5 objectives
- (Physics only) (HT only) State that loudspeakers and headphones use the motor effect.
- (Physics only) (HT only) Describe how variations in current in an electrical circuit are converted into pressure variations in sound waves.
- (Physics only) (HT only) Explain how a moving-coil loudspeaker works.
- (Physics only) (HT only) Explain how headphones use the motor effect to produce sound.
- (Physics only) (HT only) Link the motion of the coil or cone to pressure variations in the surrounding air.
Key terms
Electromagnetism evidence cue 51Electromagnetism boundary cue 52Electromagnetism application cue 53Electromagnetism measurement cue 54Electromagnetism diagnosis cue 55Electromagnetism prediction cue 56Electromagnetism comparison cue 57Electromagnetism safety cue 58Electromagnetism efficiency cue 59Electromagnetism energy-transfer cue 60Electromagnetism field-shape cue 61Electromagnetism current-change cue 62
Exam tips
- motor-effect force direction exam tip for Electromagnetism: Use motor-effect force direction explicitly, then link it to a bar magnet and plotting compass practical and state how it avoids confusing motors and generators.
- motor-effect force direction exam tip for Electromagnetism: Use motor-effect force direction explicitly, then link it to a steel core electromagnet demonstration and state how it avoids confusing motors and generators.
Common mistakes
- motor-effect force direction: avoid motors and generators: Instead, identify the exact Unit 4.7 idea in Electromagnetism, then explain how it links to a bar magnet and plotting compass practical and the objective to state that when a current flows through a conducting wire a magnetic field is produced around the wire.
- motor-effect force direction: avoid motors and generators: Instead, identify the exact Unit 4.7 idea in Electromagnetism, then explain how it links to a steel core electromagnet demonstration and the objective to describe how the strength of the magnetic field around a wire depends on current through the wire.
Practice preview
- Which explanation best links the observation to the physics? Context: National Grid substation prediction. Learning objective: State that when a current flows through a conducting wire a magnetic field is produced around the wire.. Which answer is most accurate for Electromagnetism? Distinct revision anchor: fluxcue276a coilcue276b fieldcue276c polecue276d gridcue276e motorcue276f generatorcue276g transformercue276h compasscue276i currentcue276j voltagecue276k forcecue276l.
- Which conclusion keeps the magnetism concept boundary clear? Context: classroom plotting compass prediction. Learning objective: State that when a current flows through a conducting wire a magnetic field is produced around the wire.. Which answer is most accurate for Electromagnetism? Distinct revision anchor: fluxcue277a coilcue277b fieldcue277c polecue277d gridcue277e motorcue277f generatorcue277g transformercue277h compasscue277i currentcue277j voltagecue277k forcecue277l.
- Which response uses the correct technical wording for this situation? Context: relay switch circuit prediction. Learning objective: State that when a current flows through a conducting wire a magnetic field is produced around the wire.. Which answer is most accurate for Electromagnetism? Distinct revision anchor: fluxcue278a coilcue278b fieldcue278c polecue278d gridcue278e motorcue278f generatorcue278g transformercue278h compasscue278i currentcue278j voltagecue278k forcecue278l.
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