Summary Electronics

Electricity.

 Electricity is the energy carried by the charge.
 Current is the rate of flow of charge. Measured by ammeter and SI unit is
ampere(A).
 Charge is the product of time and current. SI unit is coulomb C.
 Basic charge is the charge on an electron and its value is 1.6 x 10-19C. Quantised
mean is fixed so the charge on a particle is quantised. It cannot vary as the
charge is the integral multiple, its the basic component so cannot change.
 Number density(n): is the number of free electrons per unit volume. N/V where
N is the number of free electrons and V is the volume per m3.
 Conductivity is the conduction of charge. The higher the number density the
higher the conductivity.
 Drift velocity: the average velocity of free electrons in a conductor when the
potential difference across it. I=nAQv where n is the number density, A= the are
of cross section of wire,v= the drift velocity,I= current and Q= charge.
 Derive the relation of I=nAQv
So I=Q/t and Q=Nq as N=number density and q is the individual charge on an
electron while Q represents the total charge that passes in a specific time.
And as n=N/V so N=nv hence Q=nvq while we know that the wire is a cylindrical
shape so has the volume v = A.l
Hence Q=nAlq
Now remember I=Q/t so becomes I=nAlq/t while we can write it as : A.n.q.l/t so
l/t becomes v as l is the length for which the electrons travel and t is the time in
which they passes it is the same as v=d/t so we have derived I=Anvq
 Potential difference(V):

Electron is moving from the positive
terminal

to negative terminal. Voltmeter

measures the potential
difference . energy is provided by the
battery that

is consumed by the resistor.

Charges moves from high potential
to the

Lower potential.



1. Workdone per unit charge across two points.
2. V=W/Q where the SI unit is Volts(V) and is measured by a voltmeter.
3. The voltmeter has a very large resistance so the current cannot pass through it
thats why it is set in parallel.
4. It is workdone by the charge.

,  Shunt is a small resistance which will allow the current to pass through it.




The shunt means that green box is connected in parallel forms an ammeter.
Galvanometer could not handle larger currents so the shunt resistor is placed so it
could draw much of the current towards it.




Now it has become a voltmeter. Galvanometer is connected in series so that the small
and safe amount of current could pass. If it would be connected in parallel so
remember that the galvanometer is a low resistance device so it would draw too much
current towards itself. Here in this setup the overall resistance of the circuit increases.



Power:
 Workdone per unit time generally. P=W/t.
1. So as we know that V=W/Q where W = workdone so we can make W as a
subject so becomes W=QV and now equate in P=W/t hence it is P=VQ/t
and could be written as P=V.Q/t and Q/t is current so becomes P=VI..
2. V=IR and P=VI so the V would become P=I2R.
3. I=V/R so the equation of power becomes P=V2/R.

Hence we have derived 4 formulas to find power and have completed their derivation.



Energy:
 Energy converted per unit time.
1. E =Pt so E=Vit
2. E=I2Rt
3. E=t.V2/R.

Here we have just equate formulas of power.



Resistance:
 Potential difference per unit current
 SI unit is ohm.