Ig physics - fomrula

Density Formula

ρ= m/v

Symbol	Means	Unit
ρ (rho)	Density	g/cm³ or kg/m³
m	Mass	g or kg
V	Volume	cm³ or m³

Spring Force

F = k×x

Symbol	Means	Unit
F	Force (load) applied	newtons, N
k	Spring constant	N/m or N/cm
x	Extension = new length − original length	m or cm

Moments

M= F×d

Symbol	Means	Unit
M	Moment (turning effect)	newton-metres, Nm
F	Force applied	N
d	Perpendicular distance from the pivot to the line of action of the force	m

Object at equilibrium:

Object at Equilibrium :

sum of clockwise moments = sum of anticlockwise moments

• no turning effect

e.g.: seesaw in balance

Centre of Gravity:

Centre of gravity: The single point where the whole weight of the object acts.

Pressure Formula:

P=F/A

Symbol	Means	Unit
p	Pressure	pascals, Pa (N/m²)
F	Force pushing perpendicular to the surface	N
A	Area force acts over	m²

Pressure in Liquids

P= ρ×g×h

Symbol	Means	Unit
ρ	Density of the liquid	kg/m³
g	Gravitational field strength	N/kg (=9.8)
h	Depth below the surface	m

- Pressure increases as depth increases

Speed Formula

V= d/t

Symbol	Means	Unit
v	Speed	m/s
d	Distance travelled	m
t	Time taken	s

Velocty Formula

Velocity = Displacement/ Time

Displacement = distance but with direction

Acceleration Formula

∆Velocity/t

Symbol	Means	Unit
a	Acceleration	m/s²
v	velocity	m/s
t	Time taken for the change	s

Force Formula

F = m×a

Symbol	Means	Unit
F	Resultant force	N
m	Mass	kg
a	Acceleration (same direction as F)	m/s²

Weight Formula

W = m×g

Symbol	Means	Unit
W	Weight	N
m	Mass	kg
g	Gravitational field strength (= force per unit mass, equivalent to acceleration of free fall)	N/kg

Mass ≠ weight! Mass is constant everywhere (kg, scalar-ish quantity of matter). Weight is a force (N) that changes with g (e.g. weight on the Moon is smaller because g is smaller, but mass is unchanged)

Momentum Formula

mom = m×velocity

Symbol	Means	Unit
mom	Momentum	kg m/s
m	Mass	kg
velocity	Velocity	m/s

Impulse Formula

Impulse = ∆momentum

∆= change in

Impulse Formula- force and time

Impulse = F/ ∆t

Symbol	Means	Unit
F	Force applied	N
Δt	Time for which the force acts	s

Total meom,entum before = toalmmoemt um after

Take one direction as positive and the opposite as negative.

Conservation of energy: energy cannot be created or destroyed, only transferred from one store to another — total energy before = total energy after

Kinetic Energy

KE = ½ m×v²

Symbol	Means	Unit
KE	Kinetic energy	J
m	Mass	kg
v	Speed	m/s

Gravitational Energy

GPE = m×g×h

Symbol	Means	Unit
GPE	Gravitational potential energy	J
m	Mass	kg
g	Grav. field strength	N/kg
h	Height risen/fallen	m

Elastic Strain Energy

EPE = ½ k×x²

Symbol	Means	Unit
EPE	Elastic potential energy	J
k	Spring constant	N/m
x	Extension/compression	m

Work done

W = F×d

Symbol	Means	Unit
W	Work done (= energy transferred)	J
F	Force applied	N
d	Distance moved in the direction of the force	m

Power Formula

P = W / t  or E / t

Symbol	Means	Unit
P	Power	W (watts)
W or E	Work done or energy transferred	J
t	Time taken	s

Word done = energy transfereed

Efficenency formula

Efficiency = (useful energy/power output ÷ total energy/power input) × 100%

Symbol	Means	Unit
Useful output	Energy/power in the form you wanted	J or W
Total input	All energy/power supplied	J or W

💡 "Charge flowing per second", "rate of flow of charge" → current. Like charges repel, unlike charges attract. Charging by friction = transfer of electrons only (negative charge moves, never positive). Conventional current flows + to −; electron flow is − to + (opposite direction!).

Charge & current

I = Q / t

Symbol	Means	Unit
I	Current	amperes, A
Q	Charge passing a point	coulombs, C
t	Time	s

EMF

EMF = W / Q

Symbol	Means	Unit
EMF	Electromotive force — work done by the source driving a unit charge around the whole circuit	V
W	Work done / energy transferred	J
Q	Charge	C

V = W / Q

Voltage: Ohms law

V = I R

Symbol	Means	Unit
V	Potential difference across component	V
I	Current through component	A
R	Resistance	ohms, Ω

📐 Resistance ∝ length (longer wire = more resistance) and resistance ∝ 1/(cross-sectional area) (thinner wire = more resistance). p.d. across a conductor increases as its resistance increases, for constant current.

🔗 SERIES circuits — full rule set

• Current is the SAME at every point: I = I₁ = I₂ = I₃

• P.d. is shared: V_total = V₁ + V₂ + V₃

• EMF adds for cells in series: total EMF = EMF₁ + EMF₂ + …

• Resistance adds:

R_total= R₁ + R₂ + R₃ + …

🔗 PARALLEL circuits — full rule set

• P.d. is the SAME across every branch = same as the p.d. across the whole arrangement.

• Current is shared: current from source = sum of branch currents. I_total = I₁ + I₂ + I₃ (Kirchhoff's junction rule — current into a junction = current out).

• Current from the source is larger than the current in any single branch.

• Combined resistance of resistors in parallel is less than the smallest individual resistor.

• Advantage of parallel lighting circuits: each lamp gets full source p.d. and works independently — if one fails, the others stay on.

Potential Divider Formula

V_out = V_in × R₂ / (R₁ + R₂)

Symbol	Means	Unit
Vout	Output p.d. taken across R₂	V
Vin	Supply p.d.	V
R₁, R₂	The two resistors (or thermistor/LDR + resistor) in series	Ω

Electrical Power

P = I V

Symbol	Means	Unit
P	Electrical power	W
I	Current	A
V	Potential difference	V

Electrical Power

P = I² R

Symbol	Means	Unit
P	Electrical power	P
I	Current	A
R	Resistance	Ohms

Electricla energy transfered

E = I V t   or   P t

Symbol	Means	Unit
E	Electrical energy transferred	J
t	Time	s

Cost = power (kW) × time (h) × price per kWh — kilowatt-hour (kWh) = the energy used by a 1 kW appliance running for 1 hour.

Transformer - number of turns

V_p / V_s = N_p / N_s

Symbol	Means	Unit
Vp, Vs	Primary / secondary voltage	V
Np, Ns	Number of turns on primary / secondary coil	—

Transferomer Power (for 100% efficiency — power in = power out)

V_p I_p = V_s I_s

Magnetism basic

• Like poles repel, unlike poles attract. Field direction at a point = direction of force on a N pole placed there.

• Field lines point from N to S outside the magnet, closer lines = stronger field.

• Soft iron → temporary magnet (induced magnetism, loses it quickly). Steel → permanent magnet (keeps magnetism).

✋ Hand rules — the most examined part of this topic

Fleming's LEFT-hand rule — for the MOTOR EFFECT (force on a current-carrying wire in a field)

• ThuMb → Motion / force

• First finger → Field

• seCond finger → Current

Use when a force is being produced — motors, force on a wire/beam of charged particles.

Fleming's RIGHT-hand rule — for the GENERATOR EFFECT (electromagnetic induction)

• ThuMb → Motion of the wire (the thing you're doing)

• First finger → Field

• seCond finger → induced Current

Use when motion is producing a current — generators, induction.

💡 Memory trick: "Left = motor, Right = generator" — alphabetical (L before R, motor before generator... or just remember "FBI": First finger=Field, secBond finger=Current, thuMb=Motion, in that order for both hands).

Boyles Law

p V = constant (Boyle's Law — fixed mass of gas, constant temperature)

Symbol	Means	Unit
p	Pressure	Pa
V	Volume	m³

Often used as: p₁V₁ = p₂V₂ (Start pressure times start volume equals end pressure times end volume)

Celsius Conversion to Kelvin

T (K) = θ (°C) + 273

Symbol	Means	Unit
T	Temperature	kelvin, K
θ	Temperature	°C

Specific Heat Capacity

Q = m c Δθ

Symbol	Means	Unit
Q	Thermal energy transferred (heat)	J
m	Mass	kg
c	Specific heat capacity (energy needed to raise 1 kg by 1°C)	J/(kg°C)
Δθ	Temperature change	°C

Wave Speed

v = f λ

Symbol	Means	Unit
v	Wave speed	m/s
f	Frequency	Hz
λ (lambda)	Wavelength	m

f = 1 / T

Symbol	Means	Unit
f	Frequency	Hz
T	Period (time for one complete wave)	s

n = sin i / sin r

Symbol	Means	Unit
n	Refractive index	no unit
i	Angle of incidence (in the less dense medium, e.g. air)	degrees
r	Angle of refraction (in the denser medium)	degrees

Critical Angle

n = 1 / sin C

Symbol	Means	Unit
C	Critical angle	degrees