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SAPhysics

Topic 2: Electricity and Magnetism

8 dot points across 8 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

How do generators produce alternating voltage, and how do transformers change voltage for efficient transmission?

Explain the operation of an AC generator and apply the transformer equation to step voltage up or down.
How a rotating coil produces alternating EMF in a generator, how transformers use mutual induction to change voltage, the turns-ratio equation, and the role in power transmission.
8 min answer →

Why does a charged particle follow a circular path in a uniform magnetic field, and what sets the radius?

Analyse the circular motion of a charged particle in a uniform magnetic field, relating radius to mass, charge, speed and field strength.
Why a charge moving across a magnetic field travels in a circle, the radius equation r = mv/(qB), and its application to mass spectrometers, with worked examples.
8 min answer →

How does the electric force between charges depend on their size and separation, and what is meant by an electric field?

Apply Coulomb's law to the force between point charges and describe the electric field around a charge.
Coulomb's inverse-square law for the force between point charges, the meaning of electric field strength, and how field lines represent the field, with worked examples.
8 min answer →

How does a changing magnetic field generate a voltage, and what determines its size?

Apply Faraday's law to relate induced EMF to the rate of change of magnetic flux through a coil.
The concept of magnetic flux, how a changing flux induces an EMF, and Faraday's law relating EMF to the rate of change of flux and number of turns, with worked examples.
8 min answer →

What determines the direction of an induced current, and how does this follow from conservation of energy?

Use Lenz's law to determine the direction of an induced current and explain it in terms of conservation of energy.
How Lenz's law gives the direction of an induced current as the one that opposes the change producing it, and why this is required by conservation of energy.
7 min answer →

Why does a current-carrying wire experience a force in a magnetic field, and how is this used in motors?

Calculate the force on a current-carrying conductor in a magnetic field and explain its role in the operation of a motor.
How a current in a magnetic field feels a force F = BIL sin theta, the right-hand rule for its direction, and how this produces the turning effect in an electric motor.
8 min answer →

Why does a magnetic field only exert a force on a charge that is moving, and what determines the direction of that force?

Calculate the magnetic force on a moving charge and determine its direction using the right-hand rule.
How a magnetic field exerts a force on a moving charge, the equation F = qvB sin theta, and using the right-hand rule to find the direction, with worked examples.
8 min answer →

How does a charged particle move when it is released in the uniform electric field between two parallel plates?

Analyse the motion of charged particles in the uniform electric field between parallel plates, using field strength, force and energy.
The uniform field between parallel plates, the force and acceleration on a charge, and the energy gained across a potential difference, with worked examples.
8 min answer →