Physics formulas, constants and stuff worth remembering

Constants and formulae

Constants

1. e = 1.6 x 10^-19 C [elementary charge]
2. h = 6.63 x 10^-34 [Planck's constant]
3. m = 9.11 x 10^-31 [mass of electron]

Useful formulas

1. Impulse  = m(v-u).  Also Impulse = Force x Time (often area under F/T graph).
2. V=IR
3. P=IV and as V=IR, P=I²R
4. Internal Resistance
1. Internal resistance is resistance due to heat loss transferring electrons between anode and cathode.  EMF is the total voltage in the cell (assuming no internal resistance)
2. Terminal Voltage is the 'real' voltage - the P.D. available after internal resistance has been taken into account
3. EMF = Vterminal+ IRinternal 
5. Resistivity : Resistance = ρL/A, where ρ is resistivity, L = length (m), A = CSA (m²)
6. Number density : the number of free electrons per m³
7. Mean drift velocity - the average speed that electrons move through a medium
1. I=vAne (I = current, v = mean drift velocity (m/s), A = CSA (m), n = number density, e = elementary charge number)
8. Work Function : energy required before a material (usually metal) will emit electrons.
9. eV conversions : multiply by 'e'
1. if you have WF in Joules, then divide by 'e' to get in eV
2. if you have WF in eV, multiply by 'e' to get it in J, for example 3.2ev = 3.2 x 1.6 x 10^-19 J
10. Light/Photons etc : incident energy, E = work function + KE(max)
11. When electrons accelerated through a PD : KE = 1/2mv^2 = eV  ...often used to get the electron velocity
12. E = h/f and v = fλ
13. de Broglie λ = h/p, where p = momentum = mv
14. Young's Modulus = stress / strain

 Error handling

• When adding or subtracting : ADD ABSOLUTE errors 
• When multiplying or dividing : ADD PERCENTAGE errors
• When raising to a power : multiply error by the power
• % error = (absolute error / value) X 100

Example

Stuff worth rememberin'

1. When adding or subtracting : ADD ABSOLUTE errors
2. Photons
1. have both wave and particle properties.  Therefore a photon can be refracted and its speed will change when it moves from 1 medium to another
2. they do not contain charged particles, so are electrically neutral 
3. energy depends on frequency (or wavelength, as speed = fλ.  I)t does NOT depend on intensity!
3. polarisation : a vertical polariser followed by a horizontal polariser will let through no light.  But if you put a diagonal one between them, some light will get through.  The polarisers are not really filters..hard to explain exactly why it happens.