Year 7 Physics: Energy Stores and Transfers

Q: Which of the following is an energy transfer pathway rather than an energy store?

Correct Answer: C) Electrical working. Explanation: Electrical working is a pathway (current of moving charges) that transfers energy between stores, such as from a chemical battery store to a thermal lamp store. Mark Scheme: 1 mark for Electrical working.

Q: An electric toaster transfers 500 J of electrical energy. 420 J is transferred usefully as thermal energy to toast bread. How much energy is wasted to surroundings?

Correct Answer: B) 80 J. Explanation: Total Energy = Useful Energy + Wasted Energy. Wasted = 500 J − 420 J = 80 J (dissipated as thermal and light energy). Mark Scheme: 1 mark for 80 J with correct subtraction method.

Q: What happens to the kinetic energy store of a car when the driver applies the brakes to come to a stop?

Correct Answer: B) It is transferred mechanically by friction into the thermal energy store of the brake pads and surroundings.. Explanation: Frictional forces do work on the brakes, transferring energy from the vehicle's kinetic store into thermal energy stores, raising brake temperature. Mark Scheme: 1 mark for mechanical transfer via friction; 1 mark for thermal store of brakes/surroundings.

Key Learning Objectives

By the end of this lesson and revision module, Year 7 students will be able to:

Identify the 8 primary energy stores and the 4 pathways of energy transfer.
Apply the Law of Conservation of Energy to quantitative and qualitative scenarios.
Calculate kinetic energy, gravitational potential energy, and work done using standard KS3 formulas.

Topic Summary & Essential Notes

Energy is a fundamental concept in physics that describes the ability of a system to do work. Energy cannot be created or destroyed; it can only be transferred from one store to another. This is the Law of Conservation of Energy. The 8 main energy stores are: Kinetic (moving objects), Gravitational Potential (objects raised in a gravitational field), Chemical (foods, fuels, batteries), Thermal (hot objects), Elastic Potential (stretched or squashed springs), Nuclear (atomic nuclei), Electrostatic, and Magnetic. Energy is transferred between stores via 4 pathways: Mechanically (by forces), Electrically (by electric currents), by Heating (temperature differences), and by Radiation (light and sound waves).

Key Rules, Formulas & Definitions

Conservation of Energy

Total Energy Before = Total Energy After (Total Input = Useful Output + Wasted Output)

Work Done Equation

Work Done (J) = Force (N) × Distance moved along line of action of force (m) [W = F × s]

Gravitational Potential Energy

E_p = mass (kg) × gravitational field strength (N/kg) × height (m) [E_p = mgh]

2 Step-by-Step Worked Examples

Study these model solutions to understand how examiners award method and accuracy marks:

Worked Example 1

Worked Example 1: Energy Transfer in a Falling Object

Question: A 0.5 kg ball is dropped from a height of 4 metres. Calculate its Gravitational Potential Energy before release (g = 10 N/kg). State the energy store it transfers to as it falls.

Step-by-Step Solution:

Step 1: Formula. E_p = mass × g × height.
Step 2: Substitute values. E_p = 0.5 kg × 10 N/kg × 4 m = 20 Joules (J).
Step 3: Transfer pathway. As the ball falls, energy is transferred mechanically from its gravitational potential store to its kinetic energy store (with a small amount transferred to the thermal store of surroundings due to air resistance).

Final Answer: 20 J transferred into the Kinetic energy store.

Senior Examiner Insight: Always state the units (Joules / J). In physics exams, omitting units loses mark scheme precision marks.

Worked Example 2

Worked Example 2: Calculating Work Done

Question: A student pushes a wooden box across a laboratory bench with a constant horizontal force of 15 N over a distance of 3 metres. Calculate the work done.

Step-by-Step Solution:

Step 1: Identify formula. Work Done = Force × Distance (W = F × s).
Step 2: Insert values. W = 15 N × 3 m.
Step 3: Calculate. W = 45 Joules (J).

Final Answer: 45 J

Senior Examiner Insight: 1 Joule is defined as the work done when a force of 1 Newton moves an object through a distance of 1 metre (1 J = 1 N·m).

Common Pitfalls & Examiner Warnings

Avoid these common mistakes frequently identified by examiners in Key Stage 3 assessments:

Common Mistake: Saying energy is 'used up' or 'lost'

Energy is NEVER destroyed or used up. It is dissipated or wasted, typically transferred to thermal stores of the surrounding environment.

Common Mistake: Confusing 'energy stores' with 'energy transfers'

Light, sound, and electricity are NOT stores; they are transfer pathways.

Common Mistake: Unit mismatches (grams vs kilograms)

In calculations involving mass, ensure mass is converted to kilograms (kg) by dividing grams by 1,000.

Interactive Self-Check Quiz (3 Questions)

Test your understanding before checking the full worked answer and examiner mark scheme:

Question 1 of 3

Which of the following is an energy transfer pathway rather than an energy store?

A) Chemical energy

B) Kinetic energy

C) Electrical working

D) Gravitational potential energy

Click to Reveal Answer & Mark Scheme

Correct Answer: C) Electrical working

Detailed Explanation: Electrical working is a pathway (current of moving charges) that transfers energy between stores, such as from a chemical battery store to a thermal lamp store.

Mark Scheme & Scoring Points: 1 mark for Electrical working.

Question 2 of 3

An electric toaster transfers 500 J of electrical energy. 420 J is transferred usefully as thermal energy to toast bread. How much energy is wasted to surroundings?

A) 920 J

B) 80 J

C) 500 J

D) 420 J

Click to Reveal Answer & Mark Scheme

Correct Answer: B) 80 J

Detailed Explanation: Total Energy = Useful Energy + Wasted Energy. Wasted = 500 J − 420 J = 80 J (dissipated as thermal and light energy).

Mark Scheme & Scoring Points: 1 mark for 80 J with correct subtraction method.

Question 3 of 3

What happens to the kinetic energy store of a car when the driver applies the brakes to come to a stop?

A) It is destroyed completely.

B) It is transferred mechanically by friction into the thermal energy store of the brake pads and surroundings.

C) It is converted back into chemical fuel.

D) It turns into gravitational potential energy.

Click to Reveal Answer & Mark Scheme

Correct Answer: B) It is transferred mechanically by friction into the thermal energy store of the brake pads and surroundings.

Detailed Explanation: Frictional forces do work on the brakes, transferring energy from the vehicle's kinetic store into thermal energy stores, raising brake temperature.

Mark Scheme & Scoring Points: 1 mark for mechanical transfer via friction; 1 mark for thermal store of brakes/surroundings.

Created by Fiaraz Iqbal

Former Headteacher & Senior Science / Maths Examiner

With over 15 years of leadership and classroom experience, Fiaraz creates high-yield revision resources aligned with National Curriculum standards to help Key Stage 3 and GCSE students secure top grades.

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