Saturday, 23 April 2011

Frequency, f & Period, T - AC

Frequency, f & Period, T - AC

Example :

From the waferorm shown above :

a) Frequency, f = 2Hz
b) Period, T = 1/f
                        0.5 s (time for one cycle)

Peak value ( Amplitude) Vp :

The maximum current/voltage that can be achieved by an AC sine waveform from zero at vertical axis.

Peak-to-peak value Vpp :

That is measured from the maximum positive voltage to the maximum negative voltage ( or twice its peak value).

Example :

Peak value, Vp = 3V
Peak-to-peak value, Vpp = 3 - (-3) = 6V @
                                Vpp = 2Vp
                                        = 2 X 3V
                                        = 6V

Alternating Current Circuits - (AC)

The Differences Between (AC) & (DC)

a) Direct Current- DC

1. DC is the flow of current in one direction.
2. To generate DC, cell or battery is used.

b) Alternating Current- AC

1. AC is a type of current thet changes its direction constantly according to time.
2. Sine wave as shown below is normally used in power supply.

3. Other AC Waveforms.

Parallel DC Circuit

Parallel DC Circuit

Parallel DC circuit include as many parallel lines as desired.

1. In a parallel circuit, voltage is the same throughout each parallel leg, no matter how many legs are added.

Vs = V1 = V2 = V3

2. Current through a parallel circuit is the sum of the current in each leg.

IT = I1 + I2 + I3

3. Resistance total calculation as follows:

RT = 1 / ( 1/R1 + 1/R2 + 1/R3 )

Example : Parallel DC circuit Analysis :

Current Divider

The current divider is mostly used to determine the current on a parallel resistor circuit with only two brances.

Example :

Formula :

IRX = IT ( RT / RX )

Series DC Circuit

Series DC Circuit

All components of the series circuit are on one line from the power supply and return.

1. The voltage total is equal to the sum of the series voltage drops in the circuit :

Vs = VR1 + VR2 = VR3

2. The same current must flow through all component.

IT = IR1 = IR2 = IR3

3. The resistance total in a series circuit is the sum of the resistance in the circuit.

RT = R1 + R2 + R3....

Example : Series DC Circuit Analysis:

Voltage Divider

1. A voltage divider is used in a circuit where the resistor are connected in a series.
2. The value of the drop voltage can be easily calculated using the voltage divider formula without knowing the
3. Example :

Ohm's Law

Definition :

Ohm's Law state that the current ( I ) in a direct current electrical circuit is proportional to the voltage ( V ). And inversely proportional to the resistance ( R ). When the temperature is constant.


Voltage, current and resistance relationship are define by Ohm's Law.

Place finger over letter of unknown,
then known values and their
relationship will be uncovered;

Whenever voltage is supplies to a resistive circuit, the current will flow and generate heat. The heat is power dissipated in the resistor. The symbol is ( P ).

Formula variations of electrical power in relationship to current and voltage;

Thursday, 21 April 2011

Quantities And Units (part-2)

c) Voltage (V)

1. Voltage is the potential energy that causes the current to flow in a circuit.
2. This potential energy is produced from a battery or a generator- electromotive fore (emf)
3. The current flows from a higher pressure ( + ) to a lower pressure point ( - ).
4. The unit for the potential difference and emf is volt (V).
5. Formula:

V = I X R

d) Resistance (R)

1. Resistance is a quantity that limit the flow of a current in a circuit.
2. The important characteristic is characteristic is  : low resistance in a circuit allows high current flow, 
    however if the resistance is high the current flow in the circuit will reduced or will become zero.
3. A good conductor = a very low resistance and a good insulator = a very high resistance.
4 Formula

R = V/I

e) Power (P)

1. Power is the rate at which energy is used.
2. A watt is unit for power.
3. Formula :

P = W/T

f) Energy (E)

1. Energy is the capability to do work in a tome.
2. Energy is measured in joule. One joule is equivalent to one watt in one second.
3. Formula :

W = V X I