Don't just memorize formulas—understand them. Here's your quick-reference guide to mastering SPM Physics.
The Golden Rule
A formula is a story, not a sentence. Understand why it works, and you'll never forget it.
1. Motion & Forces
| Formula | When to Use | Quick Tip |
|---|
| v = u + at | Find final velocity | No displacement (s) needed |
| s = ut + ½at² | Find displacement | No final velocity (v) needed |
| v² = u² + 2as | Find velocity without time | No time (t) given |
| F = ma | Force from mass & acceleration | Derived from momentum change |
| W = mg | Weight of an object | g = 9.81 m/s² |
| f = μR | Frictional force | μ = roughness, R = normal force |
| F = kx | Spring force | k = spring stiffness, x = extension |
2. Work, Energy & Power
| Formula | What It Means |
|---|
| W = F × s | Work = Force × displacement |
| Eₖ = ½mv² | Kinetic energy (moving objects) |
| Eₚ = mgh | Gravitational potential energy (height) |
| P = W/t | Power = work ÷ time |
| P = Fv | Power = force × velocity (for constant speed) |
3. Electricity (High-Weightage!)
| Formula | When to Use |
|---|
| V = IR | Ohm's Law—voltage, current, resistance |
| Rₛ = R₁ + R₂ + ... | Resistors in series (add them up) |
| 1/Rₚ = 1/R₁ + 1/R₂ + ... | Resistors in parallel (reciprocal sum) |
| P = VI | Power in a circuit |
| P = I²R | Power loss as heat (use for series) |
| P = V²/R | Power when voltage is constant (use for parallel) |
| E = Pt | Energy = power × time |
4. Transformers & Electromagnetism
| Formula | What It Means |
|---|
| Vₚ/Vₛ = Nₚ/Nₛ | Voltage ratio = turns ratio |
| Pₚ = Pₛ | Ideal transformer (input = output) |
| Efficiency = (Pₛ/Pₚ) × 100% | How much power is transferred |
5. Light & Optics
| Formula | When to Use |
|---|
| n = c/v | Refractive index (c = speed of light in vacuum) |
| n₁ sin θ₁ = n₂ sin θ₂ | Snell's Law—bending of light |
| sin c = n₂/n₁ | Critical angle for total internal reflection |
| 1/f = 1/u + 1/v | Lens formula (f = focal length) |
| m = v/u | Magnification (image size vs object size) |
Lens Sign Rule: u is always negative. f is positive for convex, negative for concave.
6. Heat & Gas Laws
| Formula | What It Means |
|---|
| Q = mcΔθ | Heat to change temperature (no phase change) |
| Q = mL | Heat to change phase (melting/boiling) |
| P₁V₁ = P₂V₂ | Boyle's Law (temperature constant) |
| V₁/T₁ = V₂/T₂ | Charles' Law (pressure constant) |
| P₁/T₁ = P₂/T₂ | Pressure Law (volume constant) |
Remember: Temperature (T) must be in Kelvin (K = °C + 273).
Quick-Reference Formula Sheet
| Topic | Key Formulas |
|---|
| Motion | v = u + at, s = ut + ½at², v² = u² + 2as |
| Forces | F = ma, W = mg, f = μR, F = kx |
| Energy | W = Fs, Eₖ = ½mv², Eₚ = mgh, P = Fv |
| Circuits | V = IR, Rₛ = R₁+R₂..., 1/Rₚ = 1/R₁+1/R₂... |
| Power | P = VI, P = I²R (series), P = V²/R (parallel), E = Pt |
| Transformer | Vₚ/Vₛ = Nₚ/Nₛ, Pₚ = Pₛ |
| Light | n = c/v, n₁ sin θ₁ = n₂ sin θ₂, 1/f = 1/u + 1/v |
| Heat | Q = mcΔθ, Q = mL, PV = constant, V/T = constant |
5 Smart Strategies
- Derive, don't copy—write derivations from base principles.
- Draw diagrams—free-body diagrams, circuits, ray diagrams guide you.
- Check units—convert to SI (kg, m, s, A) before applying formulas.
- Use the right formula—know when to use each one, not just what it is.
- Teach someone—explain a formula to a friend. If you can teach it, you truly know it.
Final Checklist for Exam Day
- Write all formulas in the margin of your answer sheet first.
- Draw diagrams before attempting calculations.
- Show all working steps—you get marks for method, not just final answer.
- Check units and significant figures.
- Stay calm—you've prepared for this!
Bottom line: Understand the story behind each formula. It's not about memory—it's about mastery. Good luck! 🚀