Year 8 Science | Victorian Curriculum 2.0
Energy forms & transformations
Topic 07 | Physical sciences | Answer key

Year 8 answers

Fluency

Forms of energy

    1. (a) Chemical, (b) elastic potential, (c) kinetic, (d) gravitational potential, (e) nuclear.
    2. (a) Kinetic, (b) potential (elastic), (c) potential (gravitational), (d) kinetic.
    3. Any four of: electrical, chemical, thermal, light, sound, kinetic.
    4. Radiant (light / electromagnetic) energy.
    5. Sound: a speaker. Light: a lamp. Chemical: food or a battery.
Fluency

Heat transfer

    1. (a) Conduction, (b) convection, (c) radiation.
    2. Radiation.
    3. Plastic is a poor conductor (insulator), so the handle stays cool enough to hold while the metal stays hot in the food.
    4. The water at the bottom heats first, expands and becomes less dense, so it rises. Cooler water sinks to the bottom to take its place. This cycle repeats, creating a convection current that spreads heat through the pot.
    5. Black — it absorbs more radiant energy (while white reflects more).
Fluency

Transformations

    1. Chemical (battery) →\to electrical →\to light + heat.
    2. Chemical (petrol) →\to heat (combustion) →\to kinetic (moving pistons/wheels) + sound + heat.
    3. Torch: waste heat (bulb warms). Car: waste heat in engine and exhaust, plus sound.
    4. Energy cannot be created or destroyed, only transferred or transformed from one form to another.
    5. Friction (at the pivot) and air resistance continuously transform kinetic energy into heat. The swing’s motion decreases until it stops.
Reasoning

Efficiency

    1. η=4/10×100%=40%\eta = 4/10 \times 100\% = 40\%.
    2. η=950/1000×100%=95%\eta = 950/1000 \times 100\% = 95\%.
    3. Useful energy =25%×2000=500= 25\% \times 2000 = 500 J.
    4. Into waste heat (mostly), sound, and vibration.
Problem solving

Applied contexts

    1. Lost energy =600−540=60= 600 - 540 = 60 J. It became heat (friction between wheels and ramp, and air resistance) and a small amount of sound.
    2. Chemical (in muscles from food) →\to kinetic (running) →\to elastic potential (bending pole) →\to gravitational potential (height) →\to kinetic (falling back down).
    3. η=400/2000×100%=20%\eta = 400/2000 \times 100\% = 20\%.
    4. Double glazing traps a layer of air between two panes of glass. Air is a poor conductor, so less heat escapes in winter (or enters in summer). Lower heat loss means heaters and coolers run less, saving energy.
Reasoning

Challenge

    1. Real pendulums constantly transfer kinetic energy into heat (friction at the pivot, air resistance) and eventually stop. To run forever they would need a new energy source — which violates conservation of energy because no net energy can appear from nothing.
    2. The 200 000200\,000 J becomes heat in the brake discs and tyres (they get very hot) and a small amount of sound (screeching). Energy has not disappeared — it has spread out as thermal energy.
    3. Useful energy retained =280= 280 kJ out of 300300 kJ, so the insulation kept ∼93%\sim 93\% of the thermal energy over 10 hours. The remaining ∼7%\sim 7\% (20 kJ) leaked out via conduction through the walls and radiation from the surface.
    4. Useful electrical =35%×1000=350= 35\% \times 1000 = 350 MJ. The remaining 650650 MJ is lost mostly as waste heat at the boiler and turbine (typically carried away by cooling water or cooling towers), with smaller losses in the generator and transmission.
Year 8 Science study companion | Answer key