Unit 3: Gravity and Electromagnetism

Electric field strength as force per unit charge, the radial field of a point charge, the uniform field between parallel plates, and how field lines represent direction and strength.

Field lines around a mass, the radial gravitational potential energy formula, the area under a field-distance graph, and the work needed to move between points in a gravitational field.

Magnetic poles and field lines, permanent and temporary magnets, the field around a current-carrying wire and solenoid, electromagnets, and Earth's magnetic field including the angle of dip.

How Millikan balanced the electric force on a charged oil drop against its weight to measure the quantised elementary charge, and the calculation behind it.

Apparent weightlessness as free fall, the difference between low Earth and geostationary orbits, and Kepler's three laws including the link between period and orbital radius.

How a rotating coil in a magnetic field generates a sinusoidal alternating EMF, the role of slip rings, the difference from a DC motor, and the meaning of peak and RMS values.

The force on a current-carrying conductor and a moving charge in a magnetic field, the right-hand rule, the torque on a current loop, and how a split-ring commutator drives a direct current motor.

Work done by a force, kinetic and gravitational potential energy, the work-energy theorem, conservation of mechanical energy, and power as the rate of doing work.

Magnetic flux, Faraday's law relating induced EMF to the rate of change of flux, and Lenz's law giving the direction of the induced current from energy conservation.

Displacement, velocity and acceleration as vectors, the four constant-acceleration equations of motion, and how to read motion graphs to solve straight line problems including free fall.

Newton's three laws of motion, free body diagrams, resolving forces, and how to find net force and acceleration including weight, friction, tension and the normal force.

Linear momentum, the impulse-momentum theorem, and conservation of momentum applied to collisions and explosions in one and two dimensions.

Newton's law of universal gravitation, gravitational fields, and how combining gravity with circular motion gives orbital speed, period and Kepler's third law.

How a changing magnetic flux induces an EMF through Faraday's law, how Lenz's law fixes its direction, and how generators and transformers apply induction.

Positive and negative charge, charging by friction, conduction and induction, conservation of charge, and Coulomb's law for the force between point charges.

How to analyse projectiles by separating horizontal and vertical motion, and how a centripetal force keeps objects in uniform circular motion.

The force on a moving charge as a centripetal force, the radius and period of circular motion in a magnetic field, and applications such as the mass spectrometer and velocity selector.

Work done moving a charge through a potential difference, the electronvolt, and the parabolic and accelerated motion of charged particles in uniform electric fields.