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Chapter 11- Electricity

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Page 1: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Chapter 11- Electricity

Page 2: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Course Content • Definition of Electricity • Circuit Diagrams

– Series and Parallel Circuits

• Calculating total resistances • Measurement of Electricity

– Ammeters and Voltmeters – Ohm’s Law

• Safety Devices and Hazards • Wiring the Plug

Page 3: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

What is Electricity

• An atom is a fundamental unit of matter • made up of

• protons (with a positive charge) • neutrons (neutral – no charge) • electrons (with a negative charge)

Page 4: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

What is electricity? • Everything is made of atoms which contain POSITIVE particles called PROTONS and NEGATIVE particles called ELECTRONS.

Proton (+)

Neutron

Electron (-)

Page 5: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

What is Electricity?

• Electricity – the flow of electrons through a circuit i.e. the flow of electrical charges

• The path along which the electric current moves is called the ELECTRIC CIRCUIT

• The device which causes the flow of electrons through a circuit is called a CELL or POWER SOURCE (Battery)

Page 6: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

What is Electricity? • Electrons move round a circuit from negative

terminal to the positive terminal of the cell, producing an electric current. (note: like charges repel, opposites attract)

• The rate of flow of electric charges is called ELECTRIC CURRENT

connecting wire electric cell

filament

flow of electrons

Page 7: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Electric Current

• Conventional Current flow – electric current flows from positive terminal to negative terminal

• Alternating Current (AC) – electric current flows in a clockwise direction and then changes direction to flow anti-clockwise

• Direct Current – electric current flows only in one direction

Page 8: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Electric Current • Electric current is given the symbol, I • Can also be defined as - the amount of charge

flowing per second • Electric Current is measured in Amps (A) • Thus, Current in Amps (A) =

tQI =

Charge transferred in coulombs (C)

time in seconds (s) Current in Amps (A)

Page 9: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Electric Current

•This can be rearranged as

• or

ItQ =

IQt =

Page 10: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Electric Current • The SI Unit for Electric Current is Ampere (A) • Electric Current is measured using an

Ammeter

Page 11: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

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.

Page 12: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Electric Circuit Electric circuit :- is a continuous and closed path of an electric current. A schematic diagram of an electric circuit comprising of a cell, electric bulb, ammeter and plug key.

A +

-

+ - bulb

cell

ammeter

plug key

Page 13: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Electric Circuits • Electric circuits are

made up of electrical components

• These components must be joined together without any gap in between to form a closed circuit.

connecting wires

electric cell

circuit board light bulb

Note:

Components refer to the light bulb, wires, battery

Page 14: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Electric Circuits • Incomplete circuits are called open circuits.

connecting wire is

missing no source of

electrical energy

Both the circuits in the diagram are incomplete, hence they are known as “open circuits”.

Page 15: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

An electric current flows only when there is:

• a source of electrical energy and

• a closed circuit connecting wires

electric cell

circuit board light bulb

Page 16: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

How to draw Circuit Diagrams Component Symbol Component Symbol

An electric cell Battery

Light bulb (lamp) Switch

Switch (open)

Switch (closed)

Connecting wires (not joined)

Connecting wires (joined)

+ +

Symbols are used to represent the various electrical components in circuits.

Page 17: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3
Page 18: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3
Page 19: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Summary: Electrical Charge

• Electric charge is given the symbol

Q • Electrons are the charge carriers that

flow in an electrical circuit from the negative to positive terminals.

Page 20: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Summary: Electrical Charge

• Charge is measured in

Coulombs • which is given the symbol

C

Page 21: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Summary: Electrical Charge

• The charge on a proton is

1.6 x 10-19C

which is the same size as the charge on an electron.

Page 22: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Summary: What is electricity?

So electricity is… movement of electric charge round a

circuit. We call this electric current.

Page 23: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Summary: Charge, Current & Time

• Electric current is given the symbol

I • Electric current is the movement of

negative charges (electrons) in a circuit

Page 24: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Summary: Charge, Current & Time

• Electric Current is the amount of charge flowing per second and is given the unit

Amps (A)

Page 25: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Summary: Charge, Current & Time

•If current is charge flowing per second then

tQI =

time in seconds (s)

Current in Amps (A)

Charge transferred in coulombs (C)

so a current of 1 A is 1 C of charge transferred in 1 s.

Page 26: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Summary: Circuit Diagrams Component Symbol Component Symbol

An electric cell Battery

Light bulb (lamp) Switch

Switch (open)

Switch (closed)

Connecting wires (not joined)

Connecting wires (joined)

+ +

Symbols are used to represent the various electrical components in circuits.

Page 27: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Summary: Circuit Diagrams

Page 28: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Different types of circuit

• There are different ways in which you can connect cells and electrical components (such as lamps) to create a circuit:

series parallel a mixture of both

Page 29: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Series Circuit • A series circuit connects the components one after

the other

• A single loop is formed

• A break in any part of a series circuit stops the flow of current in the whole circuit.

Page 30: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Parallel Circuit • A parallel circuit divides into two or more branches.

• The current divides and flows through each parallel branch.

• If a component breaks or is removed, the other components remain on.

Page 31: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Voltage • An electric cell gives energy to the electrons and pushes

them round a circuit. Voltage is a measure of how much energy the electrons receive.

• Different voltages are supplied by different cells and batteries.

12 V Car Battery

1.5 V Dry Cell

9 V Dry Cell

Page 32: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

How to Measure Voltage?

• The SI unit for voltage is volt (V).

• A voltmeter is an instrument used for measuring voltages.

Page 33: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Voltmeter

• Voltmeters 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.

Page 34: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Recall: 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.

Page 35: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

measuring current

Electric current is measured in amps (A) using

an ammeter connected in series in the circuit.

A

Page 36: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

measuring current

A A

This is how we draw an ammeter in a circuit.

SERIES CIRCUIT PARALLEL CIRCUIT

Page 37: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

measuring voltage

The ‘electrical push’ which the cell gives to the current

is called the voltage. It is measured in volts (V) on a

voltmeter

V

Page 38: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

measuring voltage

V

This is how we draw a voltmeter in a circuit.

SERIES CIRCUIT PARALLEL CIRCUIT

V

Page 39: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

measuring current SERIES CIRCUIT

PARALLEL CIRCUIT

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

2A 2A

2A

• current is shared between the components

2A 2A

1A

1A

Page 40: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

fill in the missing ammeter readings.

?

?

4A

4A

4A

3A ?

?

1A

?

3A

1A

1A

Page 41: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

V

measuring voltage

V V

V

Page 42: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

series circuit

1.5V

• voltage is shared between the components

1.5V

3V

Page 43: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

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

3V

parallel circuit

3V

3V

Page 44: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

measuring current & voltage complete the missing current and voltage readings.

V V

6V 4A

A

A

a)

Page 45: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

measuring current & voltage

V

V

6V 4A A

A

A

b)

Page 46: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

answers

3V 3V

6V

4A 4A 6V

6V

6V 4A 4A

2A

2A

4A

a) b)

Page 47: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

The circuit is no longer complete, therefore current can not flow

The voltage decreases because the resistance increases. The current flow in each bulb is the same.

Page 48: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3
Page 49: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Resistance

• When an electric current flows through a circuit, there will be some resistance that opposes it. (similar to friction)

• It can be measured by dividing voltage by the current.

R = V I

R = Resistance

V = Voltage

I = Current

Page 50: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Ohm’s Law

I = V / R I = Current (Amperes) (amps) V = Voltage (Volts) R = Resistance (ohms)

Ohm’s law states that : ‘The current flowing through a conductor is directly proportional to the potential difference between its ends provided its temperature remains constant.’

Page 51: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Resistance • Good conductors of electricity have LOW

RESISTANCE. (Eg. Metal objects) – Electricity is able to flow through them very

easily • Poor conductors of electricity have HIGH

RESISTANCE. (Eg. Wood, cloth) – Electricity is not able to flow through them

easily • The SI unit for resistance is ohm (Ω)

Page 52: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Example 1 • An electric rice cooker operates at 240 V and

uses a current of 8 A. What is the resistance of the rice cooker?

Voltage (V) = 240 V

Current (I) = 8 A

R = V I

R = 240

8

= 30 Ω

Page 53: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Resistors in Series

• When resistors are connected

in series, the resistance will

add up and increase.

• R = R1 + R2 + R3… 2 Ω 3 Ω

The total resistance for this circuit is:

2 Ω + 3 Ω = 5 Ω

Page 54: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

• When resistors are connected in parallel, the resistance will decrease

• This is because they will provide alternate routes for the current to flow.

Resistors in Parallel

Page 55: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Resistors in Parallel

6 Ω

6 Ω

1 R

= 1 R

1 R

1 R

+ + 1 2 3

What is the resistance of the

circuit?

1 R

= 1 6

1 6

+

1 R

= 2 6

1 3

= R = 3Ω The final resistance is

smaller

Page 56: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Summary: Series and Parallel Circuits

Voltage, Current and Resistance Vs

I3

I2

I1

R3

+ -

R2 R1

V1 V2 V3

What type of circuit is this?

Page 57: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Vs

I3

I2

I1

R3

+ -

R2 R1

V1 V2 V3

One electrical path from negative to positive therefore series.

Page 58: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Vs

I3

I2

I1

R3

+ -

R2 R1

V1 V2 V3

What is the relationship between the three currents?

321 III ==The current is the same at each point.

Page 59: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Vs

I3

I2

I1

R3

+ -

R2 R1

V1 V2 V3

What is the relationship between the four voltages?

321 VVVVs ++=They add to equal the supply voltage.

Page 60: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Vs

I3

I2

I1

R3

+ -

R2 R1

V1 V2 V3

How do you find total resistance in series?

321 RRRRtotal ++=Add each resistance together.

Page 61: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Disadvantages of Series Circuits?

• When one component fails the whole circuit fails.

• The current is the same at all points and the

voltage is divided between the bulbs. The more bulbs added the dimmer each one is.

Page 62: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

What type of circuit is this?

IT IT

Vs

I3

I2

I1

R3

+ -

R2

R1

V1

V2

V3

Page 63: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

More than one electrical path – components connected on different branches therefore parallel.

IT IT

Vs

I3

I2

I1

R3

+ -

R2

R1

V1

V2

V3

Page 64: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

What is the relationship between the four currents?

321 IIIIT ++=

The four currents add to give the total current.

IT IT

Vs

I3

I2

I1

R3

+ -

R2

R1 V1

V2

V3

Page 65: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

What is the relationship between the four voltages?

321 VVVVS ===

Each voltage is equal to the supply voltage.

IT IT

Vs

I3

I2

I1

R3

+ -

R2

R1 V1

V2

V3

Page 66: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

321

1111RRRRT

++=

IT IT

Vs

I3

I2

I1

R3

+ -

R2

R1 V1

V2

V3

The resistance in parallel?

Page 67: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

• If more resistors are connected in parallel the total resistance will always decrease

• This is because there are more

branches through which the electricity can flow.

Page 68: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

Advantages of the Parallel Circuit?

• When one bulb fails the rest of the circuit continues to work.

• The more components, the lower the resistance. The total current drawn increases.

• Voltage in each branch is the same as the supply voltage therefore bulbs in parallel will each be as bright as a single bulb.

Page 69: Chapter 11- Electricity - NUST 11- Electricity.pdf · Chapter 11- Electricity . ... between to form a closed circuit. connecting wires . electric cell . light bulb . ... 2 Ω + 3

NOTE!! Hazards of electricity +

Safety Devices + Wiring of an Electric Plug

= Self Study