IGCSE Physics 0625 – Core Topics Overview
1. Motion – Objective (Core 1.2.1)
Know that a deceleration is simply a negative acceleration and be able to use this fact correctly in calculations.
2. Core definitions & symbols (Core 1.2.2)
| Quantity |
Symbol |
Definition |
Unit |
| Distance (scalar) |
s |
Path length travelled |
m |
| Displacement (vector) |
\(\vec{s}\) |
Shortest straight‑line distance between start and finish, with direction |
m |
| Speed (scalar) |
v |
Distance travelled per unit time |
m s‑1 |
| Velocity (vector) |
\(\vec{v}\) |
Displacement per unit time (has direction) |
m s‑1 |
| Acceleration (vector) |
\(\vec{a}\) |
Rate of change of velocity |
m s‑2 |
| Mass |
m |
Quantity of matter in an object |
kg |
| Weight |
W |
Force of gravity on a mass (W = mg) |
N |
| Force |
F |
Interaction that changes the state of motion (vector) |
N |
| Momentum |
\(\vec{p}\) |
Mass × velocity (vector) |
kg m s‑1 |
| Impulse |
\(\vec{J}\) |
Force × time = change in momentum |
N s |
| Work |
W |
Force × displacement in the direction of the force |
J (N m) |
| Power |
P |
Rate of doing work (or energy transfer) |
W (J s‑1) |
3. Key kinematic formulas (Core 1.2.3)
- Acceleration: \(\displaystyle \vec{a}= \frac{\Delta\vec{v}}{\Delta t}\)
- Velocity (constant acceleration): \(\displaystyle \vec{v}= \vec{u}+ \vec{a}t\)
- Displacement (constant acceleration): \(\displaystyle \vec{s}= \vec{u}t+\frac{1}{2}\vec{a}t^{2}\)
- Velocity–displacement relation: \(\displaystyle v^{2}=u^{2}+2as\)
- Average speed: \(\displaystyle \bar v =\frac{\text{total distance}}{\text{total time}}\)
Using deceleration in calculations
When an object slows down, its acceleration is negative (a deceleration). In equations simply substitute a negative value for \(\vec{a}\).
Example – A car travelling at 20 m s‑1 brakes uniformly to rest in 5 s.
- Identify: \(u = 20\; \text{m s}^{-1},\; v = 0,\; t = 5\; \text{s}\).
- Find the acceleration: \(\displaystyle a = \frac{v-u}{t}= \frac{0-20}{5}= -4\; \text{m s}^{-2}\). The negative sign indicates deceleration.
- Find the distance covered while stopping: \(s = ut+\frac12 a t^{2}= 20(5)+\frac12(-4)(5)^{2}=100-50=50\; \text{m}\).
4. Motion – Additional Core Content (1.1, 1.3‑1.7)
4.1 Physical quantities & measurement (1.1)
- Scales, rulers, stop‑watches, digital timers – accuracy & uncertainty.
- Average vs. instantaneous speed/velocity (gradient of a distance‑time graph).
4.2 Forces and Newton’s laws (1.3)
- Resultant force, balanced vs. unbalanced forces.
- Weight \(W = mg\) (g ≈ 9.8 m s‑2).
- Friction (static & kinetic) and its effect on motion.
- Turning moments: \(M = Fd\).
4.3 Momentum, impulse and conservation (1.4)
- \(\vec{p}=m\vec{v}\); impulse \(\vec{J}=F\Delta t = \Delta\vec{p}\).
- Conservation of momentum in isolated systems (e.g., collisions).
4.4 Work, energy and power (1.5)
- Work \(W = F s \cos\theta\).
- Kinetic energy \(E_k = \frac12 mv^{2}\); gravitational potential energy \(E_p = mgh\).
- Conservation of mechanical energy (neglecting losses).
- Power \(P = \frac{W}{t} = Fv\).
4.5 Energy resources and efficiency (1.6)
- Renewable vs. non‑renewable sources.
- Efficiency \(\displaystyle \eta = \frac{\text{useful energy output}}{\text{total energy input}}\times100\%.\)
4.6 Waves and optics basics (1.7)
- Wave terminology – crest, trough, wavelength \(\lambda\), period \(T\), frequency \(f\).
- Wave speed \(v = f\lambda\).
- Reflection, refraction and the law of reflection.
5. Thermal Physics (Core 2)
- Particle model – matter made of particles in constant motion.
- Temperature scales (Celsius, Kelvin) and conversion \(K = ^\circ\!C + 273\).
- Specific heat capacity: \(Q = mc\Delta T\).
- Phase changes: latent heat of fusion/melting and vaporisation/condensation.
- Heat transfer methods – conduction, convection, radiation.
- Practical example: Calculating the energy required to heat 250 g of water from 20 °C to 80 °C (use \(c_{\text{water}} = 4180\; \text{J kg}^{-1}\!^\circ\!C^{-1}\)).
6. Waves (Core 3)
- Transverse vs. longitudinal waves.
- Wave equation \(v = f\lambda\); use for sound and light.
- Reflection, refraction, diffraction and interference (basic concepts).
- Electromagnetic spectrum – radio, microwaves, infrared, visible, ultraviolet, X‑rays, gamma rays; everyday applications.
- Ray diagrams for mirrors and lenses (concave, convex, converging, diverging).
7. Electricity & Magnetism (Core 4)
7.1 Basic electrical quantities
- Charge \(Q\) (C), current \(I = \frac{\Delta Q}{\Delta t}\) (A), potential difference \(V\) (V), resistance \(R\) (Ω), power \(P = VI\).
- Ohm’s law \(V = IR\); series and parallel circuits.
7.2 Magnetic fields
- Field lines, Earth’s magnetic field, magnetic force on a moving charge \(F = Bqv\sin\theta\).
- Electromagnets and solenoids.
7.3 Electromagnetic induction
- Faraday’s law – induced emf \(\mathcal{E} = -\frac{\Delta\Phi}{\Delta t}\).
- Generators, transformers and the principle of a simple motor.
7.4 Safety
- Fuses, circuit breakers, earthing, RCDs.
- Safe handling of batteries and high‑voltage equipment.
8. Nuclear Physics (Core 5)
- Structure of the atom – protons, neutrons, electrons; isotopes.
- Radioactive decay types: alpha (α), beta (β), gamma (γ).
- Half‑life \(t_{1/2}\) and decay law \(N = N_0\left(\frac12\right)^{t/t_{1/2}}\).
- Applications: medical imaging, radiocarbon dating, nuclear power.
- Safety: shielding, distance, time.
9. Space Physics (Core 6)
- Earth–Sun–Moon system – rotation, revolution, seasons.
- Orbits – circular approximation, orbital speed \(v = \frac{2\pi r}{T}\).
- Phases of the Moon and eclipses.
- Basic Solar System overview – planets, moons, asteroids, comets.
10. Practical & Experimental Skills (Section 4)
Developing competence in planning, conducting and analysing investigations is essential for AO3 outcomes.
- Measuring g with a simple pendulum (period \(T = 2\pi\sqrt{\frac{L}{g}}\)).
- Determining density by water‑displacement method.
- Investigating the relationship between force, mass and acceleration (Newton’s 2nd law).
- Exploring energy transformations using a roller‑coaster model (potential ↔ kinetic).
- Mapping magnetic field lines with iron filings and a bar magnet.
- Half‑life simulation using a “decay” dice‑roll activity and plotting exponential decay.
11. Summary of the Deceleration Concept
- Deceleration = acceleration with a negative sign.
- Use the same kinematic equations; just insert the negative value for \(\vec{a}\).
- Remember: a negative velocity indicates motion opposite to the chosen positive direction; a negative acceleration indicates the velocity is becoming less positive (or more negative).
- Typical exam question: “A cyclist slows from 12 m s‑1 to 4 m s‑1 in 3 s. Calculate the deceleration and the distance covered.” – Apply the formulas above.