# Formula's

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

HideShow resource information
• Created by: sandy
• Created on: 02-09-08 12:21
Plain Text 6.3 Kb

## Pages in this set

### Page 1

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…

### Page 2

projectile only acted on by the force of gravity.

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…

### Page 3

watt = when 1 joule of energy is transferred per unit time.

hookes law = f=ke

stress = f/a

strain = e/l

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…

### Page 4

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…

### Page 5

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,

### Page 6

when the current passes through the source.

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…

### Page 7

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…

### Page 8

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…

### Page 9

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…

### Page 10

n = sini/sinr.

n1sini=n2sinr

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".…