Current Electricity

Current Electricity The movement of electric charge from

one place to another.

Voltage Potential (Voltage)-

IS THE ELECTRIC POTENTIAL PER CHARGE MOVING BETWEEN TERMINALS.

THIS IS LIKE THE ELECTRIC PRESSURE PUSHING THE ELECTRONS.

VOLTAGE DOES NOT MOVE, IT PUSHES THE ELECTRONS.

http://faraday.physics.utoronto.ca/IYearLab/Intros/DCI/Flash/WaterAnalogy.html

Low Voltage

High Voltage

Low Voltage

High Voltage

Voltage Potential (Voltage)

cont’d- Measured in volts

(V) Measured using a

voltmeter.

Current Current-

The measure of the rate at which electric charges move past a given point in a circuit.

Measures the amount of electricity passing a point.

Measured in amperes (A) Measured using an:

Ammeter- larger currents Galvanometer- smaller currents

High Current

Low Current

High Current

Low Current

Resistance Resistance

The measure of an objects opposition to the passage of a steady electrical current

Measured in ohm’s (Ω) Measured using an ohmmeter

Low Resistance High

Resistance

Low Resistance

Ohm’s law Created by Georg Ohm (1789- 1854) “the potential difference between

two points on a conductor is directly related to the electric current flowing through the conductor”

Potential difference= Electric current x electrical resistance

V = I x R

Example One

What is the voltage drop across a tungsten filament in a 100-W light bulb? The resistance of the filament is 144 Ω and a current of 0.833 A is flowing through it.

Example Two An electric toaster is connected to a

120-V outlet in the kitchen. If the heating element in the toaster has a resistance of 14 Ω, calculate the current flowing through it.

Problem solving

?Textbook (10-10)

Electrical circuits Electrical circuit-

Controlled path of flowing electricity in a complete circle

Contain 4 parts1. Source- Where electricity comes from.2. Load- Where the electrical energy is transferred.3. Control- What starts and stops the electricity. 4. Connectors- The path where the electricity runs.

Source

Control

Load

Connector

Electrical circuit- Source Cells- Converts chemical energy into

electrical energy. Batteries- combination of 2 or more

cells Generators-a device that converts

movement into electrical energy Photoelectric cells- a cell that

converts light directly into electrical energy

Cell

Battery

Generator

Photoelectric Cell

Electrical circuit- Source cont’dCells

Primary cells- Disposable cells Secondary cell- reusable cells

All cells contain:Electrodes- Metal plates that are placed in the

electrolyteElectrolytes- Chemicals that conduct electric currentPositive terminal- Place where positive charges

collectNegative terminal- Place where negative charges

collect

Electrical Sources Cells can be:

Wet cells- electrolyte is a liquid Easy to make with available chemicals Hard to transport and quite large

Electrolyte

Electrodes

Electrical Sources Dry cells- Electrolyte is a paste

Easy to transport and very compact Special and sometimes more dangerous chemicals are

required.

Electric circuit- Load Anything that converts electrical energy

into the form of energy required Light bulb (light energy) Toaster (heat energy) Television (light and sound energy) Computer (light and sound energy) Fan (mechanical energy) Music player (sound energy) Motor (mechanical energy)

Electrical circuits- Control A device that controls the flow of electrical

energy Switches

Single pole switches Double pole switches 3-way switches

Buttons Keys Timers Bimetallic strips Variable resistors (dimmer switches)

Electrical circuits-Connectors

A conducting wire that provides a controlled path for electric current to flow to each part of the circuit Conductor- A substance where electrons can

move freely from one atom to another. (electric current)

Insulator- A substance where electrons cannot move freely from one atom to another. (Static electricity)

Superconductor- Ceramics that conduct electricity with no resistance at low temperatures. (bullet trains)

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Conductor

Insulator

Superconductor

Electrical circuits Open circuit- circuit is not connected,

switch is open, no electricity is flowing Closed circuit- circuit is connected, switch

is closed, electricity is flowing Short Circuit- Circuit where there is not a

load attached to the circuit, no resistance. Can be very dangerous, connectors can become overheated and burn, cells will use up the potential very rapidly.

Open CircuitClosed Circuit

Short Circuit

Electrical circuits Electrical circuits can be made in

two different ways.1. Series circuit- One path of electric

charge

Electrical circuits2. Parallel circuit- 2 or more paths for

electric charge to follow (branches)

Electrical circuits(10-7) Connecting cells in:

Series- the potentials of the cells are added together

ie. Three 1.5V cells connected end to end has a potential of 4.5V

+

-

+ +

- -= 4.5 V

Electrical Circuits Parallel- the cells will last longer

Potential remains the same

+

-

+

-

+

-

= 1.5V

Electrical circuits Connecting loads in:

Series- Circuit potential remains the same (total) Resistance is additive Circuits current changes according to Ohm’s

law

1.5V

3 Ω

4 Ω

V= 1.5VR= 3Ω + 4Ω = 7ΩI = ?

V = I x RI = V/R

I = 1.5V/ 7Ω

I = 0.21 A

1.5V

5 Ω

7 Ω

V= 1.5VR= 5Ω + 7Ω = 12ΩI = ?

V = I x RI = V/R

I = 1.5V/ 12ΩI = 0.14 A

Electrical circuits Parallel-

Circuits potential remains the same (total) Resistance decreases Circuits current increases according to

Ohm’s law

Electrical circuits Pro’s and cons of series and parallel

circuits. Series

Pro’s Simple to make and easy to follow.

Con’s Limited control over the circuit and when one load

is broken, the entire circuit won’t work.

Electrical circuits Pro’s and cons of series and parallel

circuits. Parallel

Pro’s Lots of control over the circuit and not all loads

have to be working at the same time Con’s

Much more complex and difficult to follow.

Multimeter A multimeter is a device that can measure

potential, current and resistance in one machine.

When using a multimeter in a circuit, it must be connected properly to get a correct reading

When using as a voltmeter or ohmmeter, it must be connected in parallel to the circuit

When used as an ammeter, it must be connected in a series in the circuit

Voltmetre or ohmmetre-Connect in parallel

Multimetre

Ammetre-Connect in series Multimetr

e

Circuit schematics Schematic circuit diagrams are used

to show how electrical circuits are connected on paper.

Special symbols are used to indicate the different parts of the circuit.

- Cell

- Battery (2 cells)

- Light

M - Motor

V - Voltmeter

A - Ammeter

- Switch (1 pole)

Making a Circuit Schematic Diagram• Create a circuit that has one cell powering 1 light that is controlled by a switch.

• Create a circuit with a 3 cell battery that has 2 lights connected in series all controlled by one switch.

• Create a circuit with a 3 cell battery that has 2 lights connected in parallel all controlled by one switch, with another switch controlling just one of the lights.

Energy

Energy Energy- The ability to do work. There are many forms of energy

Light Sound Movement (mechanical) Heat Electricity Nuclear Chemical

Thermodynamics Thermodynamics is the study of

moving energy. The first law of Thermodynamics

says that: Energy cannot be created or destroyed. Energy can only be transformed from

one form to another.

Electricity

Light

Energy Transformations Toaster- Electrical energy is

converted to heat energy. The heat is produced by resistance

inside the toaster (friction)

Electricity

Heat

Energy Transformations Light Bulb- Electrical energy is

converted to light energy Light is produced by the resistance

inside the light bulb.

Electricity

Light

Energy Transformations Speaker- Electrical energy is

converted into sound energy. Sound is produced by having electricity

turn a magnet on and off. (electromagnet)

Electricity

Sound

Energy Transformations Electric motor- Electrical energy is

converted into motion (mechanical) energy. Motion is produced by creating an alternating

magnetic field. (electromagnet)

Electricity

Motion

Electromagnets A coiled wire carrying electrical

current produces a magnetic field around it. It acts like a magnet.

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Electromagnets If a piece of metal is inserted into the

coil, the metal will become magnetized.

The magnetism will only last when electricity is running through the circuit.

With an open circuit, there is no magnetic field.With a closed circuit, there is an electric field.

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Electromagnet

Metal plate

N

S

Permanent Magnet

Brushes

Wire coil

Running electricity through a wire coil produces a magnetic fieldThe similar poles ‘repel’ each other causing the wire coil to rotate.When the gap in the wire coil reaches the brushes, the magnetic field disappears.The wire coil will continue to rotate in the same direction, which will produce a new magnetic field in the same direction.This process continues producing a continuously rotating coil.

Thermodynamics The second law of thermodynamics

tells us that every time energy is transformed from one type of energy to the next type, some of the energy is transformed into an unusable form. Not all the energy is converted.

Electricity

LightHeat

Sound

Energy Loss Toaster- Electrical energy is

converted to heat energy. Energy is lost in the production of light

and sound.

Electricity

HeatLight

Sound

Energy Loss Light Bulb- Electrical energy is

converted to light energy Energy is lost as heat

Electricity

LightHeat

Energy Loss Speaker- Electrical energy is

converted into sound energy. Energy is lost as heat and motion.

Electricity

Sound

Heat

Motion

Energy Loss Electric motor- Electrical energy is

converted into motion (mechanical) energy. Energy is lost as heat and sound.

Electricity

Motion

Heat

Sound

Efficiency Efficiency is the comparison between

the amount of useful energy produced (output energy) and the original amount of energy used (input energy).

% efficiency = Useful Output Energy x 100%

Input Energy

Efficiency Energy is measured in Joules (J) A regular 60W fluorescent light bulb

produces 400J of light energy but it consumes nearly 2000J of electrical energy. What is the percent efficiency of a 60W fluorescent light bulb?

Output energy = 400JInput Energy = 2000J% efficiency = ?

% efficiency = Useful Output Energy x 100% Input Energy

% efficiency = 400J x 100%2000J

% efficiency = 20%

Can you ever have an appliance than is 100%

efficient?

No

Cost of electricity You pay for electricity based on the

amount of power you use. Power is the measure of the voltage

used and the current it was used at.P = V x I

Power is measured in Watts (W) A kW is 1000W

Cost of electricity On every electrical appliance in Canada, at

least 2 out of the following 3 items have to be included. Power Voltage Current

Only 2 have to be included because the 3rd can be calculated using the equation P = V x I.

How much power is used by a light bulb that uses 120V of potential and runs at a current of 0.83A?

V= 120V I= 0.83A P= ? P = V x I P = 120V x 0.83A P= 99.6W

What is the current used by a 60W light bulb that runs on 120V of electricity?

P= 60W V= 120V I= ? P = V x I I = P / V I= 60W / 120V I= 0.50A

Cost of electricity The cost of your electricity is based

on the amount of power you use (in kW), how long you use it (in hours), and the cost of the electricity (¢10.22/kW·h in Saskatchewan).

Cost = Power x time x rateCost = P x t x rate

How much does it cost to leave a 100W light bulb on for 8 hours in a day?

P= 100W= 0.100kW t= 8h Rate= ¢10.22/ kW·h Cost=? Cost= P x t x rate Cost= 0.100kW x 8h x ¢10.22/kW·h Cost= ¢8.2

How much does it cost to leave an equivalent 27W fluorescent light bulb on for 8 hours in a day?

P= 27W= 0.027kW t= 8h Rate= ¢10.22/ kW·h Cost=? Cost= P x t x rate Cost= 0.027kW x 8h x ¢10.22/kW·h Cost= ¢2.2

Comparing Incandescent lights to fluorescent light

For every 100W incandescent light bulb you have replaced with a 27W fluorescent light bulb, you will save ¢6 for every 8h of use.

If you replace 4 bulbs, that could be ¢24 a day.

Over 1 year that could save $87.60!

Generating electricity We have discussed several sources

of electrical energy; Cells Batteries Photoelectric cell Generator

Generating electricity The majority of our daily electricity comes

from electricity generating stations. All generating stations work on the same

principals. We discussed earlier how current

electricity in a coil produces a magnetic field. The reverse process is used to produce current electricity.

A moving magnetic field produces current electricity.

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S

NIn the presence of a magnet, the electrons are drawn in by the magnetic field.

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When the magnet moves, the electrons will be pulled along with it. The electrons are now moving, this is current electricity.

Generating electricity A generator uses the same materials

as an electric motor, but everything happens in reverse. Electric motor- current electricity

produces the spinning coil. Generator- a spinning coil produces

current electricity

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S

The electrons are drawn to one side of the magnet so the electrons flow in one direction to that side of the magnet.

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As the coil rotates, the electrons are again drawn to the one side of the magnet so the electrons make the trip again

eee As the coil continues to

rotate, current electricity continues to flow.

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Generating Electricity There are two types of electricity that

can be created: Direct current (DC)- Electricity flows in

one direction (cells, generator shown) Alternating current (AC)- Electricity

switches directions as the coil rotates.

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Direct Current (DC)

Alternating Current (AC)

Generating Electricity There are many different ways to

turn the wire coil inside the generator.

The coil is attached to a turbine, and the turbine is rotated by: Steam (coal, nuclear, natural gas,

biomass) Water Wind

Transporting Electricity Electricity has to be moved from the

generating stations to peoples houses.

Most large scale generators produce around 25 000 V of electricity.

The electricity is then moved to a transformer at the power plant which boosts the voltage to 400 000 V. Electricity travels more efficiently at higher voltages.

The high voltage electricity is then carries by thick transmission cables made of copper or aluminum.Copper and aluminum are used because of their low resistance.

The power lines go into substations near businesses, factories and homes. Here transformers change the very high voltage electricity back into lower voltage electricity.

From these substations, electricity in different power levels is used to run factories, streetcars and mass transit, light street lights and stop lights, and is sent to your neighborhood.

In your neighborhood, another small transformer mounted on pole or in a utility box converts the power to even lower levels to be used in your house.

Electricity that comes into our homes has been reduced to around 240 V.Older homes have the electricity brought in by overhead lines, newer homes have underground lines.

Before the electricity is brought into your house, it is passed through a power meter to record the amount of electricity being consumed.

After passing through the power meter it enters the house through the breaker box. There is one main breaker switch that controls all the electricity in the house. A breaker is a safety device that shuts the power off if the current becomes to high.

Main breaker switch

Inside the breaker box, the electricity can be kept at 240 V for some appliances (Oven, Furnace, etc.) or reduced to 120 V for lights and plugs. Each circuit in the house is controlled by a separate cicuit breaker.

Individual circuit breakers