Question 1

What is the law of conservation of energy?

Accepted Answer

The law of conservation of energy states that energy cannot be created or destroyed, only transferred from one store to another. The total amount of energy in a closed system remains constant. For example, when a ball is dropped, gravitational potential energy is transferred to kinetic energy, but the total energy stays the same (ignoring air resistance).

Question 2

How do you calculate efficiency in physics?

Accepted Answer

Efficiency is calculated using the formula: efficiency = (useful output energy ÷ total input energy). The result is often multiplied by 100 to give a percentage. For example, if a light bulb receives 100 J of electrical energy and produces 10 J of light, its efficiency is (10 ÷ 100) × 100 = 10%. The remaining 90 J is wasted as heat.

Question 3

What are the different energy stores?

Accepted Answer

The main energy stores are: kinetic (movement), gravitational potential (height), elastic potential (stretched or compressed materials), thermal (temperature), chemical (bonds in fuels or food), nuclear (atomic nuclei), magnetic (magnetic fields), and electrostatic (electric charges). In GCSE Physics, you'll focus on the first five most commonly.

Question 4

Why can't a device be 100% efficient?

Accepted Answer

No device can be 100% efficient because some energy is always transferred to unwanted stores, usually thermal energy due to friction or air resistance. For example, in a car engine, chemical energy is transferred to kinetic energy, but some is wasted as heat and sound. This wasted energy dissipates into the surroundings and cannot be easily reused.

Question 5

What is the difference between energy and power?

Accepted Answer

Energy is the capacity to do work, measured in joules (J). Power is the rate at which energy is transferred or work is done, measured in watts (W). One watt equals one joule per second. For example, a 60 W light bulb transfers 60 J of electrical energy into light and heat every second.

Question 6

How do you reduce unwanted energy transfers?

Accepted Answer

Unwanted energy transfers can be reduced by: lubrication (to reduce friction), thermal insulation (e.g., double glazing or loft insulation to reduce heat loss), streamlining (to reduce air resistance), and using low-resistance wires (to reduce electrical heating). These methods improve efficiency by ensuring more energy is usefully transferred.

Topic 3 – Conservation of energy

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Related Topics in EDEXCEL GCSE Physics

Topic 1 – Key concepts of physics

Topic 10 – Electricity and circuits

Topic 11 – Static electricity

Topic 12 – Magnetism and the motor effect

How to Revise Topic 3 – Conservation of energy — Edexcel GCSE Physics

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