Electronics Notes

Seite 1

Series And Parallel Circuits

Ohm's law -> V = I x R or R = V/I

Voltage and current have a directly proportional relationship.

Resistance -> A measure of the opposition it offers to the flow of electric current.

Ohmic and Non-Ohmic:

Ohmic: obeys Ohm's law

Non-Ohmic: doesn't obey Ohm's law

Ohm's law -> current and potential difference are directly proportional

Current ∝ potential difference as long as temperature is constant

What is Ohm's Law?

V = I x R

What do we mean by Non-Ohmic?

Doesn't follow Ohm's Law

Example of Non-Ohmic Conductor: Filament Lamp - Resistance of it changes with the temperature as the potential across it increases

Example of Ohmic conductor: Resistor

Total Resistance Equations:

Series: R1+R2... = Rt

Parallel: 1/R1 + 1/R2 ... = 1/Rt

Seite 2

Potential Divider Circuits and Thevenin's Theorem

Thevenin's Equations:

Step 1: Vout (V Thevenin) = (R2xVin)/(R1+R2)

Step 2: Isc = Vin/R1

Step 3: Req (R Thevenin) = Vout/Isc

Work -> changing energy from one form to another (Measured in Joules)

When electrical energy per charge is changed to another form of energy it's called potential difference.

Another form of energy re-changed to electrical is called Electromotive Force (EMF).

Power (Measure in Watts) is the rate of work done i.e. energy change per second.

IMPORTANT EQUATIONS:

Power = Energy/Time => (P = E/t) or Power = Work/Time

Current = Charge/Time => (I = Q/t)

Voltage = Energy/Charge => (V = E/Q) or Voltage = Work/Charge

Power = Current x Voltage

Power = V^2 / R or Power = I^2 x R

Steady Voltage (e.g. in cells or batteries) -> D.C - Direct Current

Oscillating Voltage (e.g. produced by generators) -> A.C - Alternating Current

Vrms = Vp/sqrt(2)

Vpeak = Vrms x sqrt(2)

Seite 3

Capacitors

The charge stored per volt is called the capacitance -> C (Farad)

C = Q/V

Unit of capacitance is farad (F)

Capacitors are used to smooth varying D.C supplies by acting as a reservoir of charge.

Capacitors easily pass A.C signals but they block D.C signals.

There are two main groups of capacitors:

Polarised

Unpolarised

Capacitance is increased when:

the area of overlap of the plates is increased

the distance between plates is decreased

an insulator (dielectric) with a higher dielectric constant is used

Factors to consider:

the tolerance

the working voltage

the leaking current

Total Capacitance Equations:

Series : 1/C1 + 1/C2 +... = 1/Ct

Parallel: C1+C2... = Ct