Quick Reference Equations (Copy)
1. Electricity
Ohm’s Law
V = I × R
- V = voltage (V)
- I = current (A)
- R = resistance (Ω)
Used in:
- V–I graphs (resistor)
- Calculating resistance from voltage and current
Power in a circuit
P = V × I
- P = power (W)
- V = voltage (V)
- I = current (A)
Used in:
- Electrical heating (e.g. immersion heater)
Energy transferred
E = P × t or E = V × I × t
- E = energy (J)
- t = time (s)
Used in:
- Specific heat capacity experiments
- Thermal energy supply
2. Forces and Springs
Hooke’s Law
F = k × x
- F = force (N)
- k = spring constant (N/m)
- x = extension (m)
Used in:
- Spring extension experiments
- F–x graph (gradient = k)
Weight
W = m × g
- W = weight (N)
- m = mass (kg)
- g = gravity (9.8 or 10 m/s²)
Used in:
- Trolley and pulley systems
- Force calculations for weights
Moment (Turning Effect)
Moment = F × d
- F = force (N)
- d = perpendicular distance from pivot (m)
Used in:
- Balanced beam or moment arm experiments
3. Motion
Speed
Speed = distance / time
- Units: m/s or cm/s
Used in:
- Trolley motion, light gate experiments, echo method
Acceleration
a = (v - u) / t
- a = acceleration (m/s²)
- u = initial velocity (m/s)
- v = final velocity (m/s)
- t = time (s)
Used in:
- Speed–time graphs, trolley on ramp
Distance from v–t graph
Distance = area under v–t graph
- If triangle:
1/2 × base × height - If rectangle:
base × height - Mixed: split into shapes
4. Waves (Sound & Light)
Wave Speed
v = f × λ
- v = speed (m/s)
- f = frequency (Hz)
- λ = wavelength (m)
Used in:
- Sound wave experiments
- Signal generator + microphone, resonance tube
Refractive Index
n = sin(i) / sin(r)
- i = angle of incidence
- r = angle of refraction
Used in:
- Refraction through glass block / semicircular block
Critical Angle
n = 1 / sin(c)
- c = critical angle (degrees)
Used in:
- Semicircular glass block, TIR experiments
5. Thermal Physics
Thermal Energy (Specific Heat Capacity)
Q = m × c × ΔT
- Q = thermal energy (J)
- m = mass (kg)
- c = specific heat capacity (J/kg°C)
- ΔT = temperature change (°C)
Used in:
- Heating water or metal block
- SHC calculation
6. Optics / Lenses
Lens Equation
1/f = 1/u + 1/v
- f = focal length (cm or m)
- u = object distance (from lens)
- v = image distance (to screen)
Used in:
- Focal length experiment using lens + screen
7. Graphs
| Graph | Formula You Apply |
|---|---|
| V vs I | Gradient = resistance (Ω) |
| F vs x (spring) | Gradient = spring constant (N/m) |
| R vs Length | Gradient shows R ∝ L |
| sin(i) vs sin(r) | Gradient = refractive index |
| 1/u vs 1/v | Intercept = 1/f (focal length) |
8. Units Summary
| Quantity | Symbol | Unit |
|---|---|---|
| Voltage | V | Volt (V) |
| Current | I | Ampere (A) |
| Resistance | R | Ohm (Ω) |
| Power | P | Watt (W) |
| Energy | E or Q | Joule (J) |
| Mass | m | Kilogram (kg) |
| Force | F | Newton (N) |
| Extension / Distance | x or d | Meter (m), cm |
| Speed | v | m/s |
| Time | t | Second (s) |
| Frequency | f | Hertz (Hz) |
| Wavelength | λ | Meter (m) |
| Temperature Change | ΔT | °C |
| SHC | c | J/kg°C |
9. High-Yield Tip
In all ATP questions, quote the formula before substitution to get method marks even if your final calculation is wrong.
Example:
R = V / I= 6.0 V / 2.0 A= 3.0 Ω