Describes electrical circuits including symbols, units and definitions, conductance and resistance, Theoretical circuits, Kirstchoffs First and Second Laws, Electrical Properties and Use of materials, Ohmic and Non-Ohmic conductors, Insulators and Conductors, Capacitors, Semi conductors.
UNIT 15: ELECTRICAL CIRCUITS AND THEIR APPLICATIONS
Section 1: Electrical symbols, units and de nitions.
SYMBOL UNIT DEFINITION
Cell
M AH milliamps x hour Battery
Switch
W (Watts) Filament lamp
Ohms Fixed resistor
K - Kelvin Thermistor
lm - lumen LED
Ohms LDR
Ohms Rheostat
F - Farad Capacitor
V - Voltage Voltmeter
A - Amperes Ammeter
Current - An electrical current is a stream of charged particles that move through an electrical
conductor or space
Potential di erence - The energy given to the charge carriers within a circuit
Electrical charge (Coulomb) - The unit given to charge that is equal to the amount of charge
produced by a current.
Resistance (Ohm) - the measure of the opposite of current that ows in a circuit.
Conductance (Siemens) - When a conductor transmits an electrical current as produced by
the electrical resistance.
electrical power - The rate at which electrical energy is transferred by an electrical circuit.
capacitance ( Farad) - the ability of a circuit to store electrical charge.
current in terms of rate of ow in mobile charge carriers - the rate at which the charge
crosses a point in a circuit in a xed amount of time
Electromotive force (EMF) - EMF is equal to potential di erence when there is no current
owing. EMF and PD are both measured in volts.
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, Conductance and resistance in relation to density of mobile charge carriers -
Conductance is the opposite of resistance as it is the measure of how easily current can ow
through circuit. In relation to density, as the relative density decreases, the availability for
conductance also decreases thus increasing resistivity.
Section 2
Energy supplied: W = Vx l x t
We use Watts to measure power (P). Energy transferred is referred to as power and the unit for
energy is joule (J)
Diagram of the theoretical circuit:
To calculate the Energy in the resistor given that V is 6.0 , t is 120 and i is 0.5 Amperes,
E= V x l x t
= 6.0 x 120 x 0.5 = 360 Joules
Kircho ’s rst and second rules
Kircho s rst law is referred to as kirchho current law and states that there is no charge lost
when the total current coming into the junction and current coming out of the junction are
equal.
Kircho s second law states that the voltage of a closed loop circuit is the total drop of each
voltage and therefore the sum of the closed loop circuit must equate to zero.
The rst law requires I1 = I2 + I3
I = Current (A)
Ohm’s Law: V = IR (Potential di erence = current x resistance)
Ohm’s law states that the current through a conductor between two points is directly
proportional to the voltage across two points.
In this theoretical circuit, the resistor has a resistance of 45 Ohms and the current is 2.5A. We
must calculate the voltage of between the two xed points.
V= IxR
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