ELECTRICITYChapter 9 Circuit Symbols Electric Current Conventional Current

ELECTRICITY-Chapter 9 Circuit Symbols Electric Current Conventional Current that is regarded to flow from positive to negative. i. e. flow of positive charge as it was earlier known. Charge Carriers Solids: Electrons Current and Drift Velocity I = n. AVe; number of electrons per cubic metre, A-crosssection area, V- velocity and e = charge of an electron. Electrolytes: Positive and negative ions Electromotive Force(EMF) Potential; difference (Voltage) Resistance Power Ratio of potential difference across a component to the current that flow through it. Measured in Ohms( ) P = IV or V 2/R or I 2 R.

Current: Is the RATE of flow of charge Current is Measured in Amperes(A) by ammeter

Drift velocity of electrons l How fast do electrons flow through a wire?

I = n. AVe 1. Calculate the drift velocity in a piece of wire where the current is 1 A, the free electron density is 5. 0 x 1028 m-3 and the diameter of the wire is 1 mm. [ans 1. 6 x 10 -4 ms-1] 2. Calculate the drift velocity of the charge carriers in a sample of semi conductor which is 5 mm wide and 2 mm thick if the current is 10 m. A and the carrier density is 6 x 1023 m-3. [10 -2 ms-1] 3. Calculate the drift velocity of electrons in a sample of copper of charge density = 6 x 1028 m-3 which has the same dimensions as the semi conductor in question 2 and also carries a current of 10 m. A. [1. 04 x 10 -7 ms-1]

Conventional current. Current that flows from positive to negative or flow of positive charge as it was earlier known. Electrons flows in opposite direction-negative to positive. An electron has a charge of: -1. 6 x 10 -19 Coulombs. e- +_ e-

Electromotive force(e. m. f) Total work done per unit charge flowing round a complete circuit. Measured in Volts The electrical energy transferred from other forms per Coulomb of charge that passes through the battery/ source. To measure e. m. f connect a voltmeter across the terminals of the battery

POTENTIAL DIFFERENCE. Potential difference ( Voltage) is energy required per Coulomb of charge to move from one point to another. V = energy = W Charge = Q Units: Volt(V) or JC-1 P. d across bulb = VA - V B

The Volt The p. d. between two points if one Joule of work is done bringing one Coulomb of charge from one point to the other. The Ohm The resistance of a component when a potential difference of 1 volt drives a current of 1 A through the conductor.

RESISTORS IN SERIES R 1 l R 2 R 3 10 15 R 3 10 In Series the total resistance is sum of all resistors. l RT = R 1 + R 2 + R 3

Calculate (a) the total resistance of the circuits (b) The current in the circuit. I=V/R 1. 5 V

RESISTANCE IN PARALLEL l In Parallel the total resistance is 1=1+1 l RT R 1 R 2 R 2 R R 33

Find (a) the total resistance (b) The current flowing in the circuit

Find the total resistance 4Ω 9Ω

What is Resistance? l Is the ratio of voltage to current flowing through a circuit. l Measured in ohms( ).

Electrical Energy l Electrical energy is energy supplied by flowing electric current. l E= voltage x Charge =QC l = Voltage x current x time. l. E= v. It

ELECTRICAL POWER l

Fuses l Fuse: piece of wire that will melt when a current of a certain size passes though it. Connected on the live wire. The fuse value needs to be just above the normal operating current