Project Topic: Electricity And Electric

Current

ByHailin K. Bennet

i. Electricityii. Electric Current iii. Electric Potential & Potential Differenceiv. Electromotive Force (emf)v. Electric Circuit and componentsvi. Current and Voltage Measurementsvii. OHM’s Lawviii. Factors Affecting Resistanceix. Combination of Resistors(Series &

Parallel)x. Heating Effect of Electricity and its apps.

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

Final GPE

Initial GPE

PotentialDifferenc

e

POTENTIAL DIFFERENCE = Work Done

(W)/Charge(Q)

V=W/QSI Unit => VOLTS

Potential Difference

1.5 V

1.5 V0 V

0 V

pd

Measuring Potential Difference

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

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.

Component Symbols – a cell

• The cell stores chemical

energy and transfers it

to electrical energy when

a circuit is connected.

• The long line is the positive end

• The short line is the negative end

Battery

• When two or more cells are connected together we call this a Battery.

• The cells chemical energy is used up pushing a current round a circuit.

• It is important that each cell faces the right way

Switch

• A switch can be open (as shown) or closed

• When the switch is open, the circuit is incomplete – no electricity can flow

Bulb / Lamp

• The lamp lights up when electricity flows through it

WiresThe wires which carry electricity consist of two parts:

• The metal wires (conductor).

• The plastic coating around the metal wires (insulator).

• Prevents people from being electrocuted.

wires

Resistor

• A resistor can change the amount of current in a circuit

• In a variable resistor, the resistance can be changed.

Fuse

• A fuse is a safety device

• When the current is too high, the fuse breaks

Example

The wire inside a 3A fuse will melt when the current is greater than 3A.

Circuit SymbolsVoltmeter

Ammeter

Variable Resistor

SwitchBulb

MotorCell

Battery

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∝IV/I = Constant

= R V =IR

R -> Ressiatance (Ω or ohm)

OHM’s Law

Fixed Resistors and Variable ResistorsFixed resistors have only one

resistance valueVariable resistors can be adjusted

to change the resistance, example- Rheostat

Fixed Resistors Rheostat

Length of Conductor ->> R∝lCross-sectional Area of conductor ->> R ∝ 1/ANature of material of conductorTemperature of conductor

R∝l/A

ρ – Constant of proportionality called Resistivity

Unit 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 togethera) Seriesb) Parallel

The components are connected end-to-end, one after the other. They make a simple loop for the current to flow round.

SERIES CIRCUITS

If one bulb ‘blows’ it breaks the whole circuit and all the bulbs go out.

PARALLEL CIRCUITS

The current has a choice of routes (paths).The components are connected side by side.

If one bulb ‘blows’ there would still be a complete circuit to the other bulb so it stays lit.

Measuring current

Electric current is measured in amps (A)

using an ammeter connected in series in

the circuit.

A

Measuring current

A A

This is how we draw an ammeter in a circuit.

SERIES CIRCUIT PARALLEL CIRCUIT

Measuring currentSERIES CIRCUIT

PARALLEL CIRCUIT

• current is the same at all points in the circuit.

6A 6A

6A

• current is shared between the components

4A4A

3A

1A

Fill in the missing ammeter readings.

?

?

4A

4A

4A

3A?

?

1A

?

3A

1A

1A

Measuring voltageThe ‘electrical push’ which the cell gives to the current is called the voltage. It is measured in volts (V) on a voltmeter

V

Different cells produce different voltages.

The bigger the voltage supplied by the cell, the bigger the current (the cell gives a bigger push to the electrons).

measuring voltage

Measuring voltage

Unlike an ammeter a voltmeter is connected across the components (in parallel)

Scientist usually use the term Potential Difference (pd) when they talk about voltage.

Measuring voltage

V

This is how we draw a voltmeter in a circuit.

SERIES CIRCUIT PARALLEL CIRCUITV

V

Measuring voltage

VV

V

Series circuit

1.5V

• voltage is shared between the components

1.5V

3V

• voltage is the same in all parts of the circuit.

3V

Parallel circuit

3V

3V

Measuring current & voltage

V V

6V4A

A

A

a)

Measuring current & voltage

V

V

6V4A A

A

A

b)

Answers

3V 3V

6V

4A 4A6V

6V

6V4A 4A

2A

2A

4A

a) b)

Heating Effect of Electric Current

When 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

Summary Uses of electricity in our daily life Sources of Electricity (Main electricity and

electric cells) Define electric current and electric circuit 4 different parts of circuits and their symbols• Connecting wires• Bulbs• Switch• Electric cell

Electric Current• Positive and negative• Pushes electrons out of the

negative terminal and round the circuit

• Flow back to the positive terminal of the cell

• Electrons are not used up only energy is used up

What is Voltage?• To measure the energy the electrons

receive• An electron can have a large amount

of potential energy at one point in the circuit

• It can also have a low amount of potential energy at another point

• The difference in potential energy between the two points is known as voltage

What is a resistor?• Appliances need to ensure that

the correct size of current flows to operate properly

• To control the size of the current, electrical components called resistors are used in the circuits

Arrangement of resistors• Parallel– For resistors in parallel, current

from the electric cell divided among the resistor

– More resistors added more electrical charges are able to flow through the resistors at the same time

– Current in circuit increases– Overall resistance of the parallel

circuit decreases

Heating Effect• Resistance in circuit wires affects

the amount of electric current flowing

• Electric current flows through the wire, the wire gets heated up

• Electrical energy to heat energy

Reference• NCERT text book Class X• Wikipedia.com• Slideshare.com