All Physics Formulas for O levels Physics by Ethan Wu
Celsius to Kelvin
ºC =K - 273.15
Factor
1012
109
106
103
10-1
10-2
10-3
10-6
10-9
10-12
Prefix
Prefix
TeraGigaMegaKiloDeciCentiMilliMicroNanoPico-
Symbol
T
G
M
k
d
c
m
µ
n
p
Formula for period of pendulum
L
T=2π√
g
T is period
L is length
G is acceleration due to gravity
Speed is the distance moved per unit
Speed = distance / time (assuming constant seed)
total distance
average speed=
total time
Velocity is the rate of change of displacement
Acceleration is the rate of change of velocity
Acceleration = (final velocity – initial velocity)/time
Newton’s 2nd Law
F (force)=m (mass) × a (acceleration)
Weight
W (weight)=m (mass)× g (gravitational field strength)
Gravitational field strength on earth = 10N/kg
On moon, 1/6 that of earth
Density
mass
Density=
volume
Compiled by Ethan Wu Ying Tang
Moment
moment=force × perpendicular distance from line of action of force to the pivot
Principle of Moment
If in equilibrium, total anticlockwise moment = total clockwise moment
Efficiency
useful energy output
Efficiency=
×100%
total energy input
Work Done
Work done=force × distance moved (must be same direction as force)
Kinetic Energy
1
Kinetic Energy= mv 2
2
Gravitational Potential Energy
Gravitational Potential Energy=mgh
m = mass
v = velocity
h = height
g = acceleration due to gravity
Power is defined as rate of work done or rate of energy conversion. (SI unit watt W)
work done or energy converted
Power=
time
Power =force × velocity
Pressure
Force
Pressure=
Area
Pressure=hρg
h = height
ρ = density of liquid
g = acceleration due to gravity
Density of mercury 13600 kg/m3
Density of water 1000 kg/m3
Compiled by Ethan Wu Ying Tang
Thermometer
𝑋𝜃 − 𝑋0
𝜃=
× 100℃
𝑋100 − 𝑋0
𝜃 = unknown temperature
𝑋𝜃 = physical property at temperature
𝑋0 = physical property at temperature at 0
𝑋100 = physical property at temperature at 100
Thermocouple
𝜀 ∝ ∆𝜃
𝜀 = emf (in V)
∆𝜃 = temperature difference between the junction
Kinetic Model of Matter
If volume fixed, pressure ∝ temperature
1
If temperature fixed, pressure ∝ volume (Boyle's law)
If pressure fixed, volume ∝ temperature
Heat Capacity
Q=C∆ θ
Specific Heat Capacity
Q=mc∆ θ
Q – thermal energy required (in J)
C – heat capacity ( in JK-1 or JºC)
c – specific heat capacity (Jkg-1K-1)
∆ θ – temperature change
m – mass of substance (in kg)
Latent heat of fusion
Lf =lf ×m
Lf – latent heat of fusion (in J)
Lf – specific latent heat of fusion (in J kg-1)
m – mass of substance (in kg)
Latent heat of vaporization
Lv =lv ×m
Lv – latent heat of vaporization (in J)
Lv – specific latent heat of vaporization (in J kg-1)
m – mass of substance (in kg)
Compiled by Ethan Wu Ying Tang
Law of reflection
i=r
i = angle of incidence, r = angle of reflection
Law of refraction (Snell’s Law)
sin 𝑖
= 𝑟𝑒𝑓𝑟𝑎𝑐𝑡𝑖𝑣𝑒 𝑖𝑛𝑑𝑒𝑥 𝑜𝑓 𝑚𝑒𝑑𝑖𝑢𝑚
sin 𝑟
C
V
N – refractive index of medium
C – speed of light in vacuum
V – speed of light in medium
N=
N=
real depth
apparent depth
Critical angle
1
sin 𝑐 =
𝑛
Speed of light = 3 x 108 m/s
The period T of a wave is the time taken to produce one complete wave. (SI unit second s)
The frequency f of a wave is the number of complete waves produced per second. (SI unit hertz Hz)
Wave speed is the distance travelled by a wave per second. (SI unit meter per second)
A wavefront is an imaginary line on a wave that joins all adjacent points that are in phase.
v = fλ
T=1/f
Sound
Amplitude proportionate to loudness
Frequency proportionate to pitch
Speed of sound in air 340m/s
Current
𝑄
𝐼=
𝑡
I = current (A)
Q = charge (C)
T = time (s)
Charge carried by 1 electron/ proton = 1.6 x 10-19 coulombs
Compiled by Ethan Wu Ying Tang
Electromotive force/potential difference
𝑊
𝜀=
𝑄
Ε = e.m.f (V)
W= work done (J)
Q = amount of charge (C)
Resistance
𝑉
𝑅=
𝐼
R = resistance of component in ohm (Ω)
V = potential difference across component (V)
I= current flowing through the component (A)
Ohm’s Law states that the current passing through a metallic conductor is directly proportional to the
potential difference across it, provided that physical conditions remain constant.
𝑉
𝑅 = = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡
𝐼
Resistivity
𝑙
𝑅=𝜌
𝐴
R-resistance (in Ω)
Ρ – Resistivity (in Ωm) constant value, depends on type of substance
l- Length (m)
A- Cross sectional area (in m2)
For a series circuit
The total resistance is the sum of individual resistances added up
For a parallel circuit
The reciprocal of the effective resistance of resistors in parallel is equal to sum of reciprocal of all the
individual resistances.
1
𝑅𝑡𝑜𝑡𝑎𝑙
=
1
1
1
+
+ ⋯+
𝑅1 𝑅2
𝑅𝑛
A potential divider is a line of resistors connected in series. It is used to provide a fraction of the voltage
of a source to another part of the circuit
R2
Vout =
×V
R 1 +R 2 ε
P=VI =I 2 R=
V2
R
E=VIt
P-power (watt W)
V-voltage
I-current
Compiled by Ethan Wu Ying Tang
E-energy
t-time
2 Formulas for Transformer
Vs Ns
=
Vp Np
Vp Ip =Vs Is
Vs output voltage
Vp input voltage
Ns number of turns in secondary coil
Np number of turns in primary coil
Is current in secondary coil
Ip current in primary coil
Efficiency of a transformer =
output power
input power
× 100%
Joule heating/ Power Loss due to heat
P = I2 R
Compiled by Ethan Wu Ying Tang