Skip to content
Marlbridge
Free trial

Flashcards · 8463 · Topic 1

Energy flashcards

27 cards on Topic 1, subtopics 4.1.1 to 4.1.3. Pick a subtopic or study them all.

Study mode needs JavaScript. Every card is listed below, so you can still cover the answers and test yourself.

All 27 cards

For a quick read-through or printing. Cover the right-hand side to test yourself. Cards marked Higher are Higher tier content only.

4.1.1 Energy changes in a system, and the ways energy is stored before and after such changes

What is a system, in energy questions?
An object or group of objects. When a system changes, energy is stored differently before and after the change, but the total amount is conserved.
Three ways the energy of a system can be changed
Heating, work done by a force, and work done when a current flows.
Kinetic energy equation, with units
Ek = ½mv² Ek in J, m in kg, v in m/s.
A moving object doubles its speed. What happens to its kinetic energy?
It quadruples (× 4), because Ek depends on v².
Elastic potential energy equation, and the condition for using it
Ee = ½ke² (k spring constant in N/m, e extension in m). It applies only within the limit of proportionality.
Gravitational potential energy equation, with units
Ep = mgh Ep in J, m in kg, g in N/kg, h (height gained) in m.
Specific heat capacity: definition and equation
The energy needed to raise the temperature of 1 kg of a substance by 1 °C. ΔE = mcΔθ (J, kg, J/kg °C, °C).
Required practical 1: what is measured, and the main source of error?
The specific heat capacity of a material: an electric heater supplies a measured amount of energy and the temperature rise is recorded. Some energy is always dissipated to the surroundings, so insulate the block.
Power: definition and two equations
Power is the rate of energy transfer (or the rate of doing work). P = E/t and P = W/t. 1 W = 1 J/s.
A 0.20 kg ball is thrown up at 8.0 m/s. What is its kinetic energy at launch?
Ek = ½ × 0.20 × 8.0² = 6.4 J

4.1.2 Conservation and dissipation of energy

Principle of conservation of energy
Energy cannot be created or destroyed, only transferred usefully, stored or dissipated.
Name the eight energy stores
Kinetic, gravitational potential, elastic potential, chemical, thermal, magnetic, electrostatic and nuclear.
Four ways energy is transferred between stores
Mechanically (by a force), electrically (by a current), by heating, and by radiation (light and sound).
What happens to “wasted” energy?
It is dissipated, usually to the thermal store of the surroundings, where it is spread out and hard to use. It is not destroyed.
Efficiency equations
efficiency = useful output energy transfer ÷ total input energy transfer efficiency = useful power output ÷ total power input No unit; × 100 for a percentage. It can never exceed 1 (100%).
Lubrication
Reduces friction between moving surfaces, so less energy is dissipated.
Thermal insulation
Reduces the rate of energy transfer by conduction.
Two properties of a wall that decide how fast a house loses energy
Its thickness (thicker → slower transfer) and the thermal conductivity of the material (lower → slower transfer).
How can the efficiency of an intended energy transfer be increased?Higher
Reduce wasted transfers: reduce friction (for example by lubrication) and reduce unwanted heating (for example by thermal insulation).

4.1.3 National and global energy resources

Renewable energy resource
One that is being (or can be) replenished as it is used.
Non-renewable energy resource
One that is not replenished as it is used. Supplies are finite, so it will eventually run out.
Which of the main energy resources are non-renewable?
Fossil fuels (coal, oil and gas) and nuclear fuel. Bio-fuel, wind, hydro-electricity, geothermal, the tides, the Sun and water waves are renewable.
Is renewable the same as reliable? Give an example.
No. Wind is renewable but unreliable (no output on still days). Coal is reliable but non-renewable.
Tidal power vs wave power: which is predictable, and why?
Tidal: tides happen at known times each day. Waves depend on the weather, so wave power is unreliable.
Environmental impacts of burning fossil fuels
Carbon dioxide is released, which contributes to global warming and climate change. Coal and oil also release sulfur dioxide, which causes acid rain.
Environmental impact of nuclear power
No carbon dioxide while running, but it produces radioactive waste that must be stored safely for a very long time, and there is a risk of a serious accident.
Science can identify an energy problem but not always solve it. Name the kinds of barrier.
Political, social, ethical and economic considerations (for example cost, energy security, local objections, lost jobs).

Revise Energy further