Key Learning Objectives
- Identify the 8 energy stores (kinetic, gravitational, thermal, chemical, elastic, magnetic, electrostatic, nuclear).
- Calculate work done, power, and efficiency using standard SI units.
- Explain the Rutherford alpha scattering experiment and the nuclear model of the atom.
Topic Summary & Core Notes
Master GCSE Physics core concepts: energy stores, system transfers, conservation of energy, power calculations (P = E/t), and nuclear radiation discoveries.
Key Rules, Formulas & Definitions
Power Formula
Power (W) = Energy Transferred (J) ÷ Time (s) [P = E / t]
Efficiency Formula
Efficiency = (Useful Energy Output ÷ Total Energy Input) × 100%
2 Step-by-Step Worked Examples
Worked Example 1
Worked Example 1: Power Calculation
Question: An electric motor lifts a 50 kg load through a height of 4.0 m in 10 seconds. Calculate the useful power output of the motor. [g = 9.8 N/kg]
Step-by-Step Solution:
- Step 1: Calculate energy transferred: Ep = m × g × h = 50 kg × 9.8 N/kg × 4.0 m = 1,960 J.
- Step 2: Calculate power: P = E ÷ t = 1,960 J ÷ 10 s = 196 W.
Final Answer: 196 W
Senior Examiner Insight: State units (Watts or J/s) clearly.
Worked Example 2
Worked Example 2: Alpha Scattering Evidence
Question: In the alpha scattering experiment, most alpha particles passed straight through gold foil, but a tiny fraction were deflected by more than 90°. What did this prove?
Step-by-Step Solution:
- Step 1: Passing through: Proved the atom is mostly empty space.
- Step 2: Large angle deflection: Proved the mass and positive charge of the atom are concentrated in a tiny central nucleus.
Final Answer: Most passed through proving atoms are mostly empty space; rare large deflections proved mass and positive charge are concentrated in a tiny central nucleus.
Senior Examiner Insight: Examiners require both conclusions: mostly empty space AND tiny dense positive nucleus.
Common Pitfalls & Examiner Warnings
Common Mistake: Confusing Energy and Power
Energy is measured in Joules (J); Power is the RATE of energy transfer measured in Watts (W = J/s).
Interactive Self-Check Quiz (3 Questions)
Question 1 of 3
What is the rate of energy transfer called?
Click to Reveal Answer & Mark Scheme
Correct Answer: A) Power
Detailed Explanation: Power is defined as the rate at which energy is transferred or work is done.
Mark Scheme & Scoring Points: 1 mark for Power.
Question 2 of 3
What unexpected result from Rutherford's experiment disproved the Plum Pudding model?
Click to Reveal Answer & Mark Scheme
Correct Answer: A) A small fraction of alpha particles were deflected backward by large angles (>90°)
Detailed Explanation: Large-angle deflections showed that positive charge was concentrated in a dense nucleus rather than spread out diffusely.
Mark Scheme & Scoring Points: 1 mark for backward deflection by dense nucleus.
Question 3 of 3
A machine has a total power input of 200 W and delivers 150 W of useful power. What is its efficiency?
Click to Reveal Answer & Mark Scheme
Correct Answer: A) 75%
Detailed Explanation: Efficiency = (Useful ÷ Total) × 100% = (150 ÷ 200) × 100% = 75%.
Mark Scheme & Scoring Points: 1 mark for 75%.
Created by Fiaraz Iqbal
Former Headteacher & Senior Science / Maths Examiner
Fiaraz produces structured video walkthroughs, Tier 3 literacy packs, and exam mark scheme breakdowns to help secondary students achieve top grades.
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