ELECRICITY

Def. of Electricity Electric Current Electric Potential & Potential Difference Electromotive Force (emf) Electric Circuit and components Current and Voltage Measurements OHM’s Law Factors Affecting Resistance Combination of Resistors(Series & Parallel) Heating Effect of Electricity and its apps.

NOTE-Direction of CONVENTIONAL Current is opposite to direction of flow of electrons.

Contents

Electricity is a form of a energy that can be easily changed to

many other forms

What is Electricity ?

Electric Current is the flow of electric charge Measured as the rate of flow of electric

charge Denoted by I

I=Q/t SI unit -> Amperes(A)

NOTE-Direction of CONVENTIONAL Current is opposite to direction of flow of electrons.

What is Electric Current ?

Electric Potential - Work done in moving a unit charge from infinity to a point

.∞ A . Potential Difference – The difference between

potential at two points

. ∞

B. A.

Electric Potential & Potential Difference

Potential difference

POTENTIAL DIFFERENCE = Work Done (W)/Charge(Q)

V=W/Q

SI Unit => VOLTS

Electromotive Force (e.m.f)

Electromotive force is the same as voltage.

E.m.f refers to the amount of energy supplied by the electric source (eg. battery) to each unit of electric charge

E.m.f is also measured by a voltmeter

Electromotive Force (e.m.f)

Potential Difference

How does an Electrical Appliance Work?

To make an electrical appliance work, electricity must flow through it.

The path along which the electric current moves is called the electric circuit.

An Electric Circuit is an electrical device that provides a path for electricity to

flow.

Electric Circuit

Circuit diagrams for open and closed circuits

Open circuit. Bulb does not light up when the switch is open.

Close circuit. Bulb will light up when the switch is closed.

Symbols

Ammeter It must be connected in series in the

circuit.

Positive side of ammeter must be connected nearest to the positive terminal of the battery (electric cell), and vice versa.

VoltmeterVoltmeters must be connected in

parallel to the circuit.The positive side of voltmeter is

connected to the positive terminal of

the cell, and vice versa.

At constant temperature, Current flowing through a conductor is directly proportional to

potential difference across its ends

V∝I

V/I = Constant = R

V=IR R -> Ressiatance(Ω or ohm)

OHM’s Law

Fixed Resistors and Variable Resistors

Fixed resistors have only one resistance value

Variable resistors can be adjusted to change the resistance, example- Rheostat

Fixed Resistors Rheostat

Length of Conductor ->> R∝l Cross-sectional Area of conductor ->> R ∝ 1/A

Nature of material of conductor Temperature of conductor

R∝l/A

ρ – Constant of proportionality called ResistivityUnit of Resistivity – ΩmMetals and Alloys have very low resistivity whereas insulators

have very high resistivity

Factors Affecting ‘R’

R= ρl/A

Resistance of a system of Resistors

There are 2 ways of joining resistors together

1.Series2.Parallel

Series Circuit

Rs = R1 +R2 + R3

Parallel Circuit

1/Rp = 1/R1 + 1/R2 + 1/R3

Heating Effect of Electric CurrentWhen an electric current flows through a wire, the wire heats up. Electrical energy has been converted into heat energy.

The greater the resistance of the wire, the greater the amount of heat produced. This heating effect is used in common electrical appliances.

Iron Kettle

The work done in moving the charge Q through a potential difference V is VQ

Therefore, the source must supply energy equal to VQ in time t.

So, power input to the circuit by the source is

P = V(Q/t)

P=VIEnergy supplied to the circuit by the source in time t is

P × t

orH= VIt H=I²Rt 

filament wire produces heat and light

In a light bulb, the heated filament which is also a resistance wire, becomes so hot that light is also emitted.

A kettle uses both copper and nichrome wires.Copper has low resistance while nichrome has high resistance.

Which material, copper or nichrome, should be used for the heating element, and for the external wire?

Use copper wire for the external wire as it has low resistance & produces less heat

Use nichrome wire for the heating element as it has high resistance& produces a lot of heat

THANK YOU