Electricity Final Presentation

7/27/2019 Electricity Final Presentation

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Electricity


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What we will Learn

What is a current?

How to draw electric circuit diagrams

What is potential difference, voltage and E.M.F? What is resistance?

S/E: Circuits arranged in series versus parallel

S/E: Fixed resistors versus variable resistors

Effects of electric current


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Types of Sources used tomake Electricity

Thermal

Geothermal

Nuclear

Hydroelectric

SolarWind


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Life without Electricity---!!!

How would you prepare your lunch?

How would you wash clothes?

Think about all the luxuries the discovery ofElectricity has brought us! No Television

No Radio

No Lights


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Inventors and Inventions

1752 Lightning Rod 1879 Light Bulb Ben Franklin Thomas Edison

1800 Electric Battery 1888 AC Power Count Alessandro Volta Nikola Tesla

1805 Refrigerator 1910 Flashlight

Oliver Evans Conrad Hubert 1876 Telephone 1920Traffic

Light

Alexander Graham Bell Garrett Morgan


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More Inventors and Inventions

1927 Television 1973 Internet Philo T. Farnsworth Vinton Cerf

1945 Computer Mauchley and Presper

1954 Microwave 1955 TV Remote

Percy Spencer Eugene Polley


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Where does Electricity come from?

Mainly 2 sources:

1) Power Stations

- Supply a lot ofelectricity

- Used in many electricalappliances

2) Electric Cells (batteries)

- Supply a little electricity

- Portable

- Safe


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Batteries are e pumps.

a. They provide a voltage

difference to a circuit.b. Types: wet-cells & dry-cells


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How does an Electrical Appliance Work?

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

The flow of electricity is called an electriccurrent.

The path along which the electric current

moves is called the electric circuit.


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What is an Electric Current???

Definition:

An electric current is the rate offlow of electric

charges in a circuit.

connecting

wire

electric

cell

filament

flow of electrons


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Electric Charges

Electric charges are made up ofpositive

charges (protons) and negative charges

(electrons).

When these charges flow in a circuit, a

current is produced.


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How does electricity flow?

The battery in a circuit gives energy to

the electrons and pushes them around

a circuit, from the negative terminal of

the cell, round the circuit and back tothe positive terminal of the cell.


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The SI unit for electric current is ampere (A).

Smaller currents are measured inmilliamperes (mA).

Different electrical components andappliances require different sizes of currentto turn them on.

How to Measure Current?

1 A = 1,000 mA

1 mA = 0.001 A


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Instrument to Measure Current

An ammeteris an instrument used for

measuring electric current.


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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.


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Electric Circuits

Electric circuits aremade up ofelectricalcomponents

These componentsmust be joinedtogether without anygap in between to

form a closed circuit.

connecting wires

electric cell

circuit boardlight bulb

Note:

Components refer to the

light bulb, wires, battery


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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.


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An electric current flows only when there is:

a source ofelectrical energy and

a closed circuitconnecting wires

electric cell

circuit boardlight bulb


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How to draw Circuit DiagramsComponent 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.


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Examples of circuit diagrams:


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Switches

A switch is used to open or close a circuit.

Main switch used in buildings

Switches used on circuit boards


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Circuit diagrams for open and closed circuits

Open circuit.Bulb does not light up whenthe switch is open.

Close circuit.Bulb will light up when theswitch is closed.


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Series and Parallel

There are 2 ways in which an electric circuit can be

arranged:

1. Series

2. Parallel


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Series Circuit

A series circuit connects the components oneafter the other

A single loop is formed

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


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Parallel Circuit

A parallel circuit divides into two or more branches.

The current divides and flows through each parallelbranch.

If a component breaks or is removed, the other

components remain on.


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Which of the following is a series circuit?Which is a parallel circuit?

Series Circuit Parallel Circuit


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Draw the circuit diagram for the following set up and

state whether it is a series or parallel circuit.


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Draw the circuit diagram for the following set up and

state whether it is a series or parallel circuit.


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Which is brighter?


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Which of the following is a series circuit?Which is a parallel circuit?

Series Circuit Parallel Circuit


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l


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Voltage

An electric cell gives energy to the electrons andpushes them round a circuit. Voltage is a measureof how much energy the electrons receive.

Different voltages are supplied by different cells andbatteries.

12 V Car Battery

1.5 V Dry Cell

9 V Dry Cell


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How to Measure Voltage?

The SI unit for voltage is volt (V). A voltmeter is an instrument used for measuring voltages.


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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.

R ll A t !!!


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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.


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Electromotive Force (e.m.f)

Electromotive force is the same as voltage.

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

E.m.f is also measured by a voltmeter


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Electromotive Force (e.m.f)


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Potential Difference (P.d.)


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R i


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Resistance

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

It can be measured bydividing voltage by the current.

R = VI

R = ResistanceV = VoltageI = Current


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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

Wi i t t f


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Wire resistance greater for:

1) Longer wires

2) Thinner wires

3) Higher temperatures

R i t


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The SI unit for resistance is ohm () Different electrical components have different resistance

For example, nichrome wires have a higher resistance than copper

wires.

Resistance

So should we use nichrome or copper to

make wires?

Ohms law


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Ohms law

Voltage DifferenceCurrent =

Resistance

I

VR


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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

Resistors


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Resistors

An electrical component that is specially made to have a

certain resistance is called a resistor. They can be connected in a circuit to resist the current

flow.


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Fixed Resistors and Variable Resistors

Fixed resistors have only one resistance value Variable resistors can be adjusted to change

the resistance.

fixed resistor symbol variable resistor symbol

Variable resistors are usefulin light dimmers and otherelectric appliances


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S/E: Resistors

Resistors can be connected in series or parallel

single resistor

extra resistor in

series results in

dimmer bulb

extra resistor in

parallel resultsin brighter bulb

Resistors connected

in SERIES

Resistors connectedin PARALLEL


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S/E: Resistors in Series

When resistors are connected

in series, the resistance will

add up and increase.

R = R1 + R2 + R32 3

The total resistance for this circuit is:

2 + 3 = 5


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When resistors areconnected in parallel, theresistance will decrease

This is because they will

provide alternate routes forthe current to flow.

S/E: Resistors in Parallel


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S/E: Resistors in Parallel

6

6

1

R=

1

R

1

R

1

R+ +

1 2 3

What is the resistance of thecircuit?

1

R =

1

6

1

6 +

1

R=

2

6

1

3= R = 3

The final resistance issmaller


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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 Hair Dryer

A k ttl b th d i h i


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A kettle uses both copperand 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 wirefor 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


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Household circuits

a. Mostly parallel.

b. 120 V in the U.S.

c. More devices plugged in a

circuit mean more current.d. More current means more heat

in the wiring.

Electric Power and Energy


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Electric Power and Energy1. Electrical power is the rate at which

electricity is converted into anotherform of energy.a. Power = current x voltage

b. Unit is the watt or kilowatt.2. Electrical energya. Energy = power x time

b. Unit is the kilowatt-hour.(1000 watts for 1 hour)

c. This is what we buy from the

electric company

Light Bulbs


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Light Bulbs

1. Incandescenta. Have a tiny

filament that resists theflow of electrons.

b. The filament gets

hot and glows toproduce light.

c. Very hot and

inefficient

2 Fluorescent


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2. Fluorescent

making it give off U-V rays.c. Phosphor absorbs U-V rays and

glows to make light.d. Very cool, efficient, and last a

long time.

a. Filled with gas

and coated withphosphor.b. Electricity

excites the gas


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Electrical safety devices

a. Fuses - one time use.

b. Circuit breakers - can be resetand reused.

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Electricity Final Presentation

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