§-Unit

Unit 3: How do fields explain motion and electricity?

10 dot points, in syllabus order. Each dot point has a focused answer, with exam-style questions and worked answers where available.

How do things move without contact?

describe electric fields using the field model, apply Coulomb's law

F = k q_1 q_2 / r^2

and the relationships

E = F/q

E = kQ/r^2

for point charges and

E = V/d

for the uniform field between parallel plates; identify the directions of field, force and acceleration of charged particles in uniform and radial fields

Electric fields. Covers the field model, Coulomb's law for point charges, the radial field $E = kQ/r^2$ , the uniform field between parallel plates $E = V/d$ , the force and acceleration on a charged particle in each, and the conventional directions used by VCAA.

11 min read →

describe magnetic fields around magnets, current-carrying wires and solenoids; apply the right-hand rule to determine the directions of fields and forces; apply

F = qvB

for a charged particle moving perpendicular to a uniform magnetic field, including circular motion of the particle

Magnetic fields. Covers field shapes around bar magnets, straight wires and solenoids, the right-hand grip and slap rules, the force on a moving charge ( $F = qvB$ ), and the resulting circular motion of a charged particle in a uniform field.

11 min read →

describe gravitation using a field model and apply Newton's law of universal gravitation

F = G m_1 m_2 / r^2

and the relationships

g = G M / r^2

g = F/m

, the work done by a gravitational field

W = \Delta U = mg \Delta h

in a uniform field and the change in gravitational potential energy in non-uniform fields as the area under a force-distance graph

Gravitational fields. Covers the field model and field lines, Newton's law of universal gravitation, the equivalence of $g$ as field strength and as acceleration, gravitational potential energy in uniform and non-uniform fields, and how to read change in $U$ as the area under a $F$ vs $r$ graph.

12 min read →

How are fields used in electricity generation?

explain the operation of AC and DC generators, distinguish between peak and RMS values of voltage and current using

V_{RMS} = V_{peak} / \sqrt{2}

and

I_{RMS} = I_{peak} / \sqrt{2}

, and apply the ideal transformer relationship

V_1 / V_2 = N_1 / N_2 = I_2 / I_1

to AC power transmission, including resistive losses

P_{loss} = I^2 R

AC and DC generators, RMS values and the ideal transformer. Covers slip rings vs split-ring commutators, the sinusoidal EMF from a rotating coil, the relationship between peak and RMS quantities, and why power is transmitted at high voltage to minimise $I^2 R$ losses.

12 min read →

investigate and apply theoretically and practically electromagnetic induction using the concepts of magnetic flux

\Phi_B = B_\perp A

, induced EMF

\varepsilon = -N \Delta\Phi_B / \Delta t

(Faraday's law) and Lenz's law to determine the direction of the induced current

Electromagnetic induction. Covers magnetic flux $\Phi_B = B_\perp A$ , Faraday's law for the induced EMF, Lenz's law for the direction of the induced current, and the standard worked example of a bar magnet falling through a coil.

11 min read →

investigate and analyse theoretically and practically the force on a current-carrying conductor in a magnetic field,

F = n B I L

, and apply this to the operation of a simple DC motor including the role of the split-ring commutator

Force on a current-carrying conductor in a magnetic field. Covers $F = n B I L$ , the right-hand slap rule, the torque on a current loop, and the operation of a simple DC motor including the role of the split-ring commutator in keeping the rotation in one direction.

11 min read →

How do physicists explain motion in two dimensions?

model the force vectors acting on an object on a banked track moving in uniform circular motion in a horizontal plane and identify the design speed at which friction is not required to keep the object on the track

Banked tracks. Covers the free-body diagram of a car on a banked curve, the derivation of the design speed at which no friction is needed ( $\tan\theta = v^2 / rg$ ), and the worked example for a typical motorway off-ramp.

9 min read →

investigate and analyse theoretically and practically the uniform circular motion of an object moving in a horizontal plane and on a vertical circle, including a quantitative analysis of the forces acting at the top and bottom of the vertical circle

Circular motion. Covers centripetal acceleration and force, the period-speed-radius relationships, the conical pendulum on a horizontal circle, and the forces at the top and bottom of a vertical loop (roller coasters, buckets of water, balls on strings).

11 min read →

investigate and apply theoretically and practically Newton's three laws of motion in situations where two or more coplanar forces act along a straight line and in two dimensions; apply the concepts of momentum and impulse, including the conservation of momentum in one and two dimensions, and distinguish between elastic and inelastic collisions

Newton's laws, momentum and impulse. Covers force, mass and acceleration in two dimensions, impulse as the area under a force-time graph, conservation of momentum in 1D and 2D collisions, and how to tell elastic from inelastic collisions.

11 min read →

investigate and analyse theoretically and practically the motion of projectiles near Earth's surface including a qualitative description of the effects of air resistance

Projectile motion. Covers resolving the launch velocity into independent horizontal and vertical components, applying constant-velocity equations horizontally and SUVAT vertically with $g = 9.8$ m/s squared, the standard worked range and maximum height example, and a qualitative treatment of air resistance.

9 min read →