TECHNOLOGYELECTRICITY AND ELECTRICAL

CIRCUITS

-

BASIC CONCEPTS

Liezel Oosthuizen200932201

What is electricity?The flow of electrons in the form of an electric charge

What are the two types of electricity?

a. Static electricity

b. Current electricity

What is static electricity?

When two objects rub against each other electrons transfer and build up on an object causing it to have a different charge from its surroundings.

Like the shoes rubbing against the carpet. Electrons are transferred from the carpet to the shoes.

As electrons collect on an object, it becomes negatively charged. As electrons leave an object it attains a positive charges. Charges interact with each other:

Often when you remove clothes from the clothes dryer, they seem to stick together. This is because some of the clothes have gained electrons by rubbing against other clothes. The clothes losing electrons become positive. The negative clothes are attracted to the positive clothes.

Have you ever rubbed a balloon on your hair and stuck it on a wall? How do you think this works?

What causes you to be shocked when you rub your feet across carpet?

An electrical discharge is the passing of an electric current through the air from a negatively charged object to a positively charge object. This is what causes lightning!

What is current electricity?

a. Negative charges that move along a path or wire

How is current electricity different from static electricity?

a. Current electricity travels in a path made by a wire

b. Static Electricity doesn’t travel in a path or wire

wiring

battery

voltmeter

ammeter

resistance

capacitor

+ -

A

V

junction

terminal

AC generator

Variableresistance

Variablecapacitor

ELECTRIC CIRCUITS

In an electric circuit, an energy source and an energy consuming device are connected by conducting wires through which electric charges move.

(1) A source voltage, that is, an electron pump usually a battery or power supply.

[ ENERGY IN]

(2) A conductor to carry electrons from and to the voltagesource (pump). The conductor is often a wire.

[ENERGY TRANSFER]

(3) A load or resistance. A point where energy is extractedform the circuit in the form of heat, light, motion, etc.

[ENERGY OUT]

All electrical circuits require three elements.

Voltage Source(Potential Rise)

Low Energycurrent

High Energycurrent

Resistance(Potential Drop)

Low Energycurrent

High Energycurrent

What are electric circuits?Circuits typically contain a voltage source, a wire conductor, and one or more devices which use the electrical energy.

What is a series circuit? A series circuit is one which provides a single pathway for the current to flow. If the circuit breaks, all devices using the circuit will fail.

What is a parallel circuit?A parallel circuit has multiple pathways for the current to flow. If the circuit is broken the current may pass through other pathways and other devices will continue to work.

RESISTANCE

Resistance (R) – is defined as the restriction of electron flow. It is due to interactions that occur at the atomic scale.

For example, as electrons move through a conductor they are attracted to the protons on the nucleus of the conductor itself. This attraction doesn’t stop the electrons, just slow them down a bit and cause the system to waste energy.

The unit for resistance is the OHM, W

PotentialIn volts

(joules / coul)

CurrentIn amperes

(coul / second)

ResistanceIn ohms

(volts / amp)

Drop across a resistance

Current passingThrough the

resistor

Electrical Calculations – What is Ohm’s Law?

I =

3 V2 Ω

I = 1.5 amps

How is Electrical Power calculated?

Electrical Power is the product of the current (I) and the voltage (v)

The unit for electrical power is the same as that for mechanical power in the previous module – the watt (W)

Example Problem: How much power is used in a circuit which is 110 volts and has a current of 1.36 amps?

P = I V

Power = (1.36 amps) (110 V) = 150 W

How is electrical energy determined?Electrical energy is a measure of the amount of power used and the time of use.

Electrical energy is the product of the power and the time.

Example problem:

E = P X time

P = I V

P = (2A) (120 V) = 240 W

E = (240 W) (4 h) = 960Wh = 0.96 kWh

REFERENCING Ch 20 Electric Circuits. (n.d.). Retrieved March 19, 2012, from

http://www.slideshare.net/cscottthomas/ch-20-electric-circuits-online

Electric circuits. (n.d.). Retrieved March 19, 2012, from http://www.slideshare.net/jmemler/electric-circuits-10520910

Electrical Circuits. (n.d.). Retrieved March 19, 2012, from http://www.slideshare.net/wsautter/electrical-circuits

Electricity and Magnetism - Basic Concepts. (n.d.). Retrieved March 19, 2012, from http://www.slideshare.net/makadelhi/electricity-and-magnetism-basic-concepts

Electricity.Electronics Ch20. (n.d.). Retrieved March 19, 2012, from http://www.slideshare.net/Wansyi/electricityelectronics-ch20-presentation

Ohm’s law. (n.d.). Retrieved March 19, 2012, from http://www.slideshare.net/wathens/ohms-law-7892325

chapter-12-lesson4-electricity-1216167849986490-8.ppt. (n.d.). Retrieved from http://s3.amazonaws.com/ppt-download/chapter-12-lesson4-electricity-1216167849986490-8.ppt?response-content-disposition=attachment&Signature=2JTi69Np8a%2FhUaX0pWkNUl139K4%3D&Expires=1331653554&AWSAccessKeyId=AKIAJLJT267DEGKZDHEQ