Physics of Electronics

Physics of Electronics

Finish the sentence, “When force isn’t constant…

Acceleration is also not constant

Define an ‘Electric field’

The force experienced per unit positive charge on a small test charge

Give 2 formulas for Electric field

E = F/q = q/4πε₀r²

State the principle of superposition

For a system of charges, the total electric field & total electric potential can be found by adding the individual fields and potentials arising from each individual charge

What happens to a charge when it moves in the same direction as the electric force

It gains KE

What happens to a charge when it moves in the opposite direction as the electric force

It gains PE

Define ‘Current Density’

The rate of flow of charge per unit area (Am⁻²)

How do you obtain the average drift velocity for a defined no of electrons

The velocity of each electron/no of electrons

Give the formula for the number density of a wire/conductor

n = N/V

N = total no of electrons

V = Volume of the wire

Give the formula for drift velocity

V = (eE/m)τ

e - electron charge

E = Electric field
m = mass

τ = Mean time collision(Scatter time)

Give the formula for Current density

J = nev

n - number density

e - electron charge

v - drift velovity

Define ‘Mobility’

The average drift velocity per unit electric field

Define ‘Conductivity’

The degree to which a specific material conducts electricity

Give the formulae for conductiviy

σ = ne²τ/m = neμ

σ = conductivity

n = number density

e = electron charge

τ = Mean collision time(scattering time)

μ = Mobility

What happens when you have a large mean free time

You get a large mobility which results in a large velocity.

Define ‘Diffusion Current’ and what the movement of electronss are like

The flow of charge carriers within a semiconductor. Electrons move from an area of higher concentration to an area of lower concentration

Give the formula for diffusion current

r = (1/A)(dn/dt)

A = area

(dn/dt) = the rate of change of number of electrons per unit area

What is the inverse of conductivity and under what condition is this the case?

Resistivity (σ=1/ρ). This only occurs in one dimension.

Give the formula for diffusion current density

J = QT

J = Diffusion current density

Q = Charge of particles

T = Diffusion Flux

Give the formulae for the Diffusion constant

D = l²/τ = 

D = diffusion constant

l = length

τ = mean scattering time

What causes the diffusion of electrons

The concentration gradient

Give another formula for Total Current density

J = neμE_x + eD_e (dn/dx)

E_x=Electric field

μ = mobility

dn/dx = rate of change of e- concentration with respect to x(position)

Give the formula for no of e- in a shell

2(2l + 1)

Give the formula for magnetic force

F = BILsinα

B = Magnetic field

I = current 

L = length of conductor

Sinα = angle between conductor and field

Give the formula for flux

φ = BACosθ
A = area

Cosθ = angle between field and the normal to the plane of the area of the object

Give the formula for flux linkage

φ = BACosθ
A = area

N = Number of turns

Cosθ = angle between field and the normal to the plane of the area of the object

Give the formula for induced voltage in an EMF

V = V₀Sin(2πft)

where V₀ = BAN2πf