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Magnetic fields
This A-level only topic links moving charges, magnetic fields and electromagnetic induction.
0
Objectives
10
Flashcards
10
Questions
90 min
Study time
AqaA LevelPhysicsFields and their consequences
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Syllabus checklist
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Magnetic flux density4 objectives
- Define magnetic flux density using force on a current-carrying conductor.
- Calculate force on a conductor in a magnetic field.
- Determine force direction using a suitable hand rule.
- Required practical 10: investigate force on a wire in a magnetic field.
Moving charges in a magnetic field4 objectives
- Calculate magnetic force on a moving charged particle.
- Explain circular motion of charged particles in uniform magnetic fields.
- Link magnetic force to centripetal force.
- Determine path direction for charged particles.
Magnetic flux and flux linkage4 objectives
- Define magnetic flux and flux linkage.
- Calculate flux linkage for coils in magnetic fields.
- Explain how changing flux linkage induces emf.
- Required practical 11: investigate magnetic flux linkage using a search coil.
Electromagnetic induction4 objectives
- Use Faraday's law to calculate induced emf.
- Use Lenz's law to determine the direction of induced effects.
- Explain induction in generators and transformers.
- Interpret flux-time and emf-time graphs.
Alternating currents4 objectives
- Describe alternating current using period, frequency and peak value.
- Use rms values for current and voltage.
- Interpret AC graphs.
- Calculate power in AC circuits using rms values where appropriate.
The operation of a transformer4 objectives
- Explain transformer action using changing magnetic flux.
- Use transformer turns ratio equations.
- Apply power and efficiency relationships to transformers.
- Explain why transformers are useful in power transmission.
Key terms
Magnetic Flux DensityForce on a Current-Carrying ConductorForce on a ConductorRight-Hand RuleForce DirectionMagnetic flux densityForce on a conductorMagnetic ForceLorentz ForceCentripetal forceCentripetal ForcePath direction of charged particles
Exam tips
- Understanding Magnetic Flux Density: Use the field type first, then identify the source quantity, direction, equation or graph, and unit before writing the final conclusion for Magnetic fields. Compare gravitational, electric, magnetic, orbital and transformer contexts explicitly so your answer does not transfer a rule from the wrong field model.
- Calculating Force on a Conductor: Use the formula F = BIL to calculate the force on a conductor in a magnetic field, where F is the force, B is the magnetic flux density, I is the current, and L is the length of the conductor.
Common mistakes
- Misunderstanding Magnetic Flux Density: To define magnetic flux density (B), use the formula B = F / (I * L), where F is the force on the conductor, I is the current, and L is the length of the conductor in the magnetic field. Substitute the known values to find B, ensuring to express the units correctly as teslas (T).
- Forgetting the Direction of Force: To fix this, remember to use the right-hand rule: point your thumb in the direction of the current, your fingers in the direction of the magnetic field, and your palm will face the direction of the force.
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