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Hooke’s law
Extension is directly proportional to force until the spring reaches its elastic limit.
F=kx
Ohm’s law
The current in a metal wire at constant temperature is directly proportional to the potential difference across it.
V=IR
Stefan’s law
The luminosity of a star is proportional to the fourth power of the star’s temperature and directly proportional to its surface area.
L∝T^4∝A
L=4π²x
Principle of conservation of momentum
Assuming no external forces act, momentum is always conserved. Total momentum before collision = total momentum after the collision.
Newton’s third law
If an object A exerts a force on object B then B exerts a force equal of magnitude in the opposite direction.
Newton’s second law
The rate of change of momentum of an object is directly proportional to the net force which acts on the object.
Force = Δp / Δt
Newton’s first law
Velocity of an object won’t change unless another force acts on the object.
Snells law
Use this to calculate refractive index
N1xsin1=N2xsin2
Conservation of Mass-Energy
Energy can’t be lost or gained only transferred between sources.
E=mc²
Newtons law of gravitation
The gravitational force between 2 particles is proportional to the product of their masses.
Mm∝1/r²
Coulomb’s law
The electrostatic force ( F) between 2 small bodies is proportional to the product of their charges and inversely proportional to their separation squared.
F∝Qq∝1/r²
Kepler’s first law
The orbit of each planet around the sun is an ellipse with the suit at one foci
Kepler’s second law
A line joining the sun to a planet sweeps out equal areas in equal times
Keplers third law
The square of the orbital period of a planet is directly proportional to the cube of the mean distance between the planet and the sun.
T² ∝r³
Hubble’s law
The recessional velocity of a galexy is directly proportional to its distance away from earth.
v= Ho d
Weins Displacement law
Maximum wavelength is inversely proportional to the stars temperature.
λmax= k/T
Lenzs law
Induce EMF opposes the direction of the change of flux linkage that caused it.
The minus sign in Faradays law
Boyles law
Pressure is inversely proportional to volume for a fixed mass of gas at a constant temperature.
P ∝ 1/v
Charles’s law
Volume is directly proportional to the absolute temperature for a fixed mass of gas at constant pressure.
V∝T
Pressure law
Pressure is directly proportional to absolute temperature for a fixed mass of a gas at constant volume
P ∝ T
Kirchhoffs First law
The sum of the current entering any junction is equal to the sum of the currents leaving the junction.
Conservation of charge
Kirchoffs Second law
The sum of the emf is equal to the sum of the potential difference in a closed loop.
Conservation of energy
Doppler effect
Change in frequency due to relative motion between source and observer.
Archimedes principle
When an object is partly submerged in fluid it experiences an upthrust equal to the weight of the fluid that has been displaced.
Ideal gas assumptions
Perfectly elastic collisions
Large number of particles
The volume of the particles is negligible compared to the volume of gas
Rapid and random motion
No forces between particles except collisions
Luminosity
Total radiant power of a star
Radio waves
10^1 - ^-6
Pass through matter
Radio transmissions
Microwaves
10^-3 - ^-1
Mostly pass through matter, some heating
Radar
Microwave cooking
TV transmissions
Infrared (IR)
7×10^-7 - ^-3
Mostly absorbed by matter, heating
Heat detectors
Night vision cameras
Remote controls
Optical fibres
Visible light
4×10^-7 - 7x 10^-7
Absorbed by matter, causing some heating
Human sight
Optical fibres
Ultra violet (UV)
10^-8 - 4×10^-7
Absorbed by matter, slight ionisation
Sun beds
Security marks
X-rays
10^-13 - 10^-8
Mostly pass through matter, causes ionisation
See damage to bones and teeth
Airport security
Kill cancer cells
Gamma rays
10^-16 - 10^-10
Mostly pass through matter, cause ionisation
Irradiation of food
Sterilisation
Kill cancer cells