Physics
Physics
Mechanics, waves, electricity, magnetism, and modern physics — complete physics cheatsheet for A-Level.
01Mechanics▼
Speed
v=d/t
d=distance, t=time.
Acceleration
a=(v-u)/t
v=final, u=initial velocity.
SUVAT
v=u+at, s=ut+1/2at^2, v^2=u^2+2as
Constant acceleration.
Force
F=ma
Newton's 2nd law.
Momentum
p=mv
Conserved in collisions.
Impulse
J=Ft=delta(mv)
Change in momentum.
| SUVAT equation | Missing variable |
|---|---|
| v=u+at | s |
| s=ut+1/2at^2 | v |
| v^2=u^2+2as | t |
| s=1/2(u+v)t | a |
02Energy & Work▼
Work done
W=Fs*cos(theta)
F=force, s=displacement, theta=angle.
KE
KE=1/2mv^2
Kinetic energy.
GPE
GPE=mgh
Gravitational potential energy.
Power
P=W/t=Fv
Rate of doing work.
Efficiency
useful output/total input x 100%
Hooke's Law
F=kx
k=spring constant, x=extension.
PHYSICSEnergy conservation
GPE -> KE: mgh=1/2mv^2 -> v=sqrt(2gh) Energy is conserved in closed systems. In elastic collision: KE conserved. In inelastic: momentum conserved, KE not.
03Waves▼
Wave speed
v=f*lambda. v=speed, f=frequency, lambda=wavelength.
Period
T=1/f. Period=1/frequency.
Transverse
Oscillation perpendicular to travel. Light, EM waves.
Longitudinal
Oscillation parallel to travel. Sound.
Refraction
Snells law: n1*sin(theta1)=n2*sin(theta2)
Diffraction
Waves spread around obstacles. Significant when lambda~gap.
Interference
Superposition: constructive (in phase), destructive (out of phase).
💡
Speed of light in vacuum = 3x10^8 m/s. Sound in air = 340 m/s. Light slows when entering a denser medium.
04Electricity▼
Ohms Law
V=IR
V=voltage, I=current, R=resistance.
Power
P=IV=I^2*R=V^2/R
Electrical power.
Energy
E=Pt=IVt
Electrical energy.
Series R
R_total=R1+R2+...
Same current through each.
Parallel R
1/R=1/R1+1/R2+...
Same voltage across each.
Charge
Q=It
Q=charge, I=current, t=time.
PHYSICSKirchhoffs laws
KVL (Voltage): sum of EMFs = sum of voltage drops in a loop KCL (Current): current in = current out at a junction For battery with internal resistance r: V_terminal = EMF - I*r
❓ Quiz
What is the unit of electrical resistance?
Resistance is measured in Ohms (symbol: omega). V=IR so Ohm = Volt/Ampere.
05Magnetism & Fields▼
Magnetic force
F=BIL (on wire), F=Bqv (on charge). B=flux density.
Right hand rule
Thumb=current, fingers curl=field direction.
Flemings left hand
thumb=motion, index=field, middle=current.
Gravitational field
g=GM/r^2. F=mg. Attractive only.
Electric field
E=F/q=kQ/r^2. Can attract or repel.
Coulombs law
F=kQ1Q2/r^2
k=8.99x10^9 Nm^2/C^2
Gravitational
F=Gm1m2/r^2
G=6.67x10^-11 Nm^2/kg^2
06Modern Physics▼
| Topic | Key equation | Value/fact |
|---|---|---|
| Photon energy | E=hf | h=6.63x10^-34 J.s |
| Photoelectric | hf=phi+1/2mv^2 | phi=work function |
| de Broglie | lambda=h/p=h/mv | Wave-particle duality |
| Radioactive decay | N=N0*e^(-lambda*t) | lambda=decay constant |
| Half-life | t1/2=ln2/lambda | Time for N to halve |
| E=mc^2 | Mass-energy equivalence | c=3x10^8 m/s |
PHYSICSNuclear equations
Alpha decay: A -> B + He-4 (Z-2, A-4) Beta-minus: neutron -> proton + electron + antineutrino Gamma: no change in Z or A, just energy released Fission: large nucleus splits (nuclear reactors) Fusion: small nuclei combine (stars, future energy)