Coaching Centre
Energy on the move review
A summary of the whole Energy on the Move chapter, every formula with its units, key words, and a mixed test covering heat transfer, sound, light and the electromagnetic spectrum, reflection and refraction, Ohm's law, series and parallel circuits, power, efficiency and energy resources.
Use this page to check the whole chapter. Read the summary, make sure you can use every formula and explain every key word, then do the test without looking back.
Chapter summary
| Topic | What you need to know |
|---|---|
| 6A Heat transfer and insulation | Heat flows hot → cold. Conduction (particle collisions; free electrons in metals), convection (less dense warm fluid rises), radiation (infrared, needs no medium). Insulators trap still air. House heat loss through ceiling, walls, windows, floor, draughts; heat flow = U × A × ΔT. Eaves, north-facing windows, thermal mass, double glazing. Heat pumps move 3 to 5 J of heat per J of electricity. Possum-skin cloaks; Budj Bim stone houses. |
| 6B Sound waves | Waves carry energy, not matter. Sound is a longitudinal mechanical wave: compressions and rarefactions. Wavelength, frequency (Hz), period, amplitude. v = f λ; speed set by the medium (air 343 m/s at 20 °C, water 1480, steel 5900; faster in warmer air; none in a vacuum). Pitch ↔ frequency, loudness ↔ amplitude. Hearing 20 to 20 000 Hz; decibels; noise damage above 85 dB. Echoes: distance = speed × time ÷ 2 (sonar, ultrasound, echolocation). Yidaki resonance. |
| 6C Light and the EM spectrum | Light is a transverse EM wave, 3 × 10⁸ m/s in a vacuum. Crest, trough, amplitude, wavelength. White light = all colours; objects reflect some colours and absorb others. Radio, microwave, infrared, visible, UV, X-ray, gamma: shorter λ = higher f = more energy. UV, X-ray and gamma are ionising. c = f λ. UV safety. Murriyang (Parkes) and SKA-Low on Wajarri Yamaji Country. |
| 6D Reflection, refraction and lenses | Angle of incidence = angle of reflection, measured from the normal. Plane mirror image: virtual, upright, same size, laterally inverted. Concave mirrors converge, convex diverge. Refraction is caused by a change of speed: slower → towards the normal. n = c ÷ v. Critical angle and total internal reflection; optic fibres. Convex lenses converge (long sight), concave lenses diverge (short sight). |
| 6E Voltage, current and resistance | Current I = Q ÷ t (amps). Voltage = energy per coulomb (volts). Ammeter in series, voltmeter in parallel. Resistance (ohms) increases with length, thinness and temperature. Ohm's law V = I R. Ohmic resistor: straight I–V line through the origin; filament lamp: curve. Resistor colour code. |
| 6F Series, parallel and power | Series: same current, voltages add, R = R₁ + R₂. Parallel: same voltage, currents add, total R less than the smallest branch. P = V I. Energy (kWh) = kW × h; cost = kWh × price. House wiring in parallel: active, neutral, earth; circuit breakers protect wiring; RCDs protect people. Mains is 230 V. |
| 6G Efficiency and energy resources | Overall efficiency = product of each step. Transmission loss = I² R, so high voltage, low current; transformers step up and down. Australia's mix is moving from coal to solar, wind and storage. Precipitators, scrubbers, low-NOₓ burners; CCS has under-delivered. UNSW's PERC solar cell. Batteries and pumped hydro. First Nations Clean Energy Network. |
Formulas
| What | Formula | Units |
|---|---|---|
| Heat flow through a wall or window | heat flow = U-value × area × temperature difference | W, W/m²/°C, m², °C |
| Wave equation | v = f λ (for EM waves, c = f λ) | m/s, Hz, m |
| Period | T = 1 ÷ f | s, Hz |
| Echo distance | distance = speed × time ÷ 2 | m, m/s, s |
| Refractive index | n = c ÷ v | no units |
| Current | I = Q ÷ t | A, C, s |
| Voltage | voltage = energy ÷ charge | V, J, C |
| Ohm's law | V = I R | V, A, Ω |
| Series resistance | R = R₁ + R₂ | Ω |
| Parallel resistance (two branches) | 1/R = 1/R₁ + 1/R₂ | Ω |
| Power | P = V I | W, V, A |
| Energy used and cost | energy = power × time; cost = energy × price | kWh, kW, h; c/kWh |
| Efficiency | efficiency = useful out ÷ total in × 100; chains multiply | % |
| Transmission loss | P(lost) = I² R | W, A, Ω |
Putting it together
Every topic in this chapter is about energy getting from one place to another. Heat moves by particles bumping (conduction), fluids flowing (convection) or waves (radiation). Sound carries energy as a wave of vibrating particles, while light and the rest of the electromagnetic spectrum carry it as waves that need no particles at all, and both obey v = f λ. Light changes direction when it changes speed, which lets us build lenses, glasses and optic fibres. In a circuit, charges carry energy from a battery or power station to the components: voltage tells you how much energy each coulomb carries, current how many coulombs flow per second, and their product is the power. At every step some energy spreads out as heat, so engineers insulate houses, use high-voltage transmission lines and choose efficient devices, and society is choosing energy sources that waste less and pollute less.
Key words
ammeter · amplitude · circuit breaker · compression · conduction · conventional current · convection · coulomb · critical angle · current · decibel · diffuse reflection · dispersion · earth wire · echo · efficiency · electromagnetic spectrum · focal point · frequency · heat pump · hertz · infrared · insulator · ionising radiation · kilowatt-hour · lateral inversion · longitudinal wave · normal · ohm · Ohm's law · optic fibre · parallel circuit · pitch · power · rarefaction · RCD · refraction · refractive index · resistance · series circuit · sonar · thermal mass · total internal reflection · transformer · transverse wave · ultrasound · virtual image · voltage · voltmeter · wavelength
Test yourself
Which statement about convection is correct?
Convection needs a fluid; warmer parts expand, become less dense and rise.
A sound has a frequency of 500 Hz and a wavelength of 0.68 m. Its speed is
v = f λ = 500 × 0.68 = 340 m/s.
Compared with visible light, gamma rays have
Gamma rays are at the short-wavelength, high-frequency end of the spectrum. All EM waves have the same speed in a vacuum.
A ray of light goes from glass into air at an angle smaller than the critical angle. It
Light speeds up going into air, so it bends away from the normal.
A 230 V hair dryer draws 8 A. Its power and resistance are
P = V I = 230 × 8 = 1840 W; R = V ÷ I = 230 ÷ 8 = 28.75 Ω.
Three identical lamps are connected in parallel to a 6 V battery. The voltage across each lamp is
In parallel, each branch gets the full supply voltage.
A wind farm is 40% efficient and the grid is 90% efficient. A kettle is 85% efficient. The overall efficiency is about
0.40 × 0.90 × 0.85 = 0.306, about 31%.
Label the refraction diagram.
Sort the ways energy can travel.
Order these from the lowest to the highest frequency.
Light is a wave. Light bends when it passes into glass because its changes. A voltmeter is connected in . Ohm's law states that V = . Electricity bills charge for energy in . Electricity is sent over long distances at voltage.
A family wants to cut its electricity bill. Using at least three ideas from this chapter, explain the science behind three changes they could make, and include one calculation to support your answer.
First, put insulation batts in the ceiling and seal draughts. Batts trap still air, a very poor conductor that cannot form convection currents, so less heat escapes and the heater runs for less time. Second, replace a 2000 W electric panel heater with a reverse-cycle air conditioner. The panel heater converts each joule of electricity into one joule of heat, but the heat pump moves about four joules of heat from the outside air for each joule of electricity, so it needs only about 500 W for the same warmth. Running 6 hours a day for 90 days, the panel heater uses 2 kW × 540 h = 1080 kWh, costing 1080 × $0.33 = $356, while the heat pump uses about 270 kWh, costing about $89, a saving of about $267. Third, replace incandescent globes with LEDs. An incandescent globe turns only about 5% of its electrical energy into light and the rest into heat, while an LED converts about 40%, so an LED needs roughly an eighth of the power for the same light. Because P = V I and energy = power × time, lower-power devices use fewer kilowatt-hours and cost less.