# Formula's

Some formula's on forces and motion, electrons and photons, wave properties, which helped me get through the exams.

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• Created by: sandy
• Created on: 02-09-08 12:21

First 86 words of the document:

Forces and Motion.
Vector is any physical quantity with magnitude and direction.
Scalar is any physical quantity with magnitude but no direction.
Speed is change of distance per unit time.
Velocity is change of displacement per unit time.
acceleration is change of velocity per unit time.
a= vu/t
s= ut+1/2at^2
v^2=u^2+2as
s= (vu)t/2
s=d/t
Principle of conservation of energy.
Energy cannot be created or destroyed.

## Other pages in this set

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Moment of a force = fd
principle of moments sum of the clockwise moments = sum of the anticlockwise moments.
w1d1=w2d2
2"pie"r/T = constant speed in a circle
Thinking distance the distance a car travels from the point the driver sees the hazard to when
the brakes are applied
vt
braking distance the distance a car travels from the point the brakes are applied to the point
where the car stops.…read more

### Page 3

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Youngs modulus = stress/strain
force = ma
Newtons first law when an object is at rest or constant velocity it will remain in equilibrium
unless acted on by a force.
Potential energy = mgh
kinetic energy = 1/2mv^2
Weight = mg
Couple 2 Opposite equal forces acting on an object but not along the same line.…read more

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Density = m/v
Pressure = F/A
Elastic energy stored per unit volume 1/2stressstrain
Elastic energy stored in a stretched wire 1/2fe
The centre of gravity is where the weight of a body is considered to act.
Unstable equilibrium will not return to as the centre of gravity is directly above the point of force.
stable equilibrium will return as the centre of gravity is directly below the point of force.…read more

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Q=IT
R=V/I
V=W/Q
P=IV
P=I^2R
P=V^2/R
R = R1 + R2 etc
1/R= 1/R1 + 1/R2
W=IVt
p=RA/L
conductivity (SM1) = 1/resistivity
Internal Resistance E = IR +Ir (r= (E/I)R)
Internal resistance of a source is the loss of potential difference per unit current in the source,…read more

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Kirchhoffs Laws
1st law = at a junction the total current going in is equal to the total current coming out.
2nd law = the sum of the emf's in a circuit is equal to the sum of the potential differences.
Ohms law states that in a metallic conductor the current is directly proportional to the potential
difference if conditions stay the same.…read more

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Photon is a quantum of energy
E = hf
Ek = hf WorkFunction
fmin = work function/plancks constant
DeBrogliesWavelength = h/mv
G X U L I M R
wavelength = speed/frequency
Power of beam = nhf
Potential difference is work done per unit charge.
E.M.F of a source of electricity is defined as the electrical energy per unit charge produced inside

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E.g. sound.
Compressions and Rarefactions.
Longitudinal waves do not change amplitude, they just travel along a wave.
Transverse waves are waves in which vibration is perpendicular to the direction in which the
wave travels.
E.g. light.
Transverse waves oscillate oscillate with an amplitude and are polarised as they oscillate
perpendicular to the direction of the wave.
Phase difference is the difference between identical points on different waves.
Polaroid allows oscillation in one direction.
Wavespeed = wavelength x frequency.
Wave patterns from deep to shallow.…read more

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Reflection.
Angle of incidence = angle of reflection.
2 laws.
1. Angle between the incident ray and normal = the angle between the reflected ray and the
normal.
2.Incident ray, reflected ray and normal are in the same plane.
Refraction.
Bending of light from one material to the other.
refractive index = speed in air/speed in medium.
ci/cr.
If light enters a medium of HIGHER refractive index the light will bend towards the normal.…read more

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Critical angle is the angle of incidence for which the angle of refraction is 90"degrees".
n= 1/sinc.
When i is less than c light refracts out.
when i is less than c light reflects back in.
when i is equal to c light leaves at 90"degrees".
Fibre optics
Multipath dispersion is where waves follow different paths along a fibre.
Monomode is where the fibre is so small only one path for waves is present and therefore there
is no multipath dispersion.…read more