Unit 34 Electricity

Unit 34 Concepts of Electricity

What is electricity?

Electric Charge

Do you remember how ions form in chemistry?

• Ions form when atoms gain or lose electrons. To acquire their charge, positive ions lose electrons and negative ions gain electrons.

• If electrons are lost to another atom, then an atom would become positively charged.

• If electrons are gained from another atom, then an atom would become negatively charged.

Electric Current =

Electricity is a form of energy carried by the movement of electrons.

The electrons of some atoms, like those of copper and other metals, are only loosely attached, which allows electricity to travel through these materials easily. These types of materials are known as “conductors.”

An outside force—such as light, heat, pressure, or a chemical reaction—can cause electrons to break free and get “bumped” from one atom to the next. A sequence of electrons then passes from atom to atom.

This continuous flow of electrons from atom to atom through a conductor is called electric current.

Electric ChargeCharges that are the same repel each other.

Charges that are different attract each other.

Electric ForceAn electric field is a region around a charged

object where the object’s electric force is exerted on other charged objects.

Electric ForceAn electric field is a region around a charged

object where the object’s electric force is exerted on other charged objects.

Transferring ChargeThere are three methods by which charges can

be transferred to build up static electricity: charging by friction, by conduction, and by induction.

Transferring ChargeThere are three methods by which charges can

be transferred to build up static electricity: charging by friction, by conduction, and by induction.

What is Induction?

When a substance gains a charge without touching another substance, it is said to have gained its charge through induction.

Example: you are about to touch a door knob and you get shocked!!!!!

Quick Quiz

What happens when you get shocked by static electricity?

A. Electrons are transferred from one object to another.

B. Protons are transferred from one object to another.

C. Neutrons are transferred from one object to another.

D. Positrons are transferred from one object to another.

Quick Quiz

What happens when you get shocked by static electricity?

A. Electrons are transferred from one object to another.

B. Protons are transferred from one object to another.

C. Neutrons are transferred from one object to another.

D. Positrons are transferred from one object to another.

Types of CurrentThere are two types of current: direct current (DC)

and alternating current (AC).

• Batteries provide DC voltage to an object. There are several types of batteries such as AAA, AA, C, D, 9 Volt. Of these batteries, the 9 Volt provides the most voltage and the D has the greatest amount of stored energy in it.

 • Alternating current (AC) is a type of electric current you

find in your home. Alternating current is a flow of electric current that will regularly reverse its direction. The electric current can flow forwards and backwards!

Flow of Electric ChargesElectric current is the continuous flow of

electric charges through a material.

An Electric CircuitAn electric circuit is a complete, unbroken

path through which electric charges can flow.

ResistanceTwo factors that affect the resistance of

water flowing in a pipe are diameter and length. The diameter and length of a wire also affect resistance in a circuit.

Ohm’s Law

Georg Ohms

Increasing voltage increases the current

Increasing the resistance will decrease the current (if voltage is held constant).

• The relationship between voltage and current is a directly proportional. This means that as one variable increases, the other increases (or as one decreases, the other decreases).

• The relationship between current and resistance is inversely proportional. This means as one variable increases, the other decreases and vice versa.

Electrical Equations 

Voltage = Volts Current = Amps Resistance = Ohms

Volts = joules/coulombAmperes = coulombs/second

Voltage = Current x Resistance  

Current = Voltage ÷ Resistance 

Resistance = Voltage ÷ Current

Question Answer

Electrical Power = Watts

What is electric power? Electric power is the rate at which electrical energy is transformed into another form of energy.

James Watt

Watts = Joules/second

Volts * Amps = Watts

Electric PowerThe rate at which energy is transformed from

one form to another is known as power. Power is measured in watts (W).

Electric Circuits• There are two main types of electrical circuits: series and

parallel.

• In a series circuit the current must be distributed throughout the elements of the circuit. This means that none of the elements are getting the same amount of current as they would if they were alone in the circuit.

• A parallel circuit allows more than one path for the current to flow. This allows for multiple elements to be placed within the circuit, and each of these elements will receive the same amount of electricity, as it would if were the only element in the circuit.

Kilowatt Hours

A Watt is a joule/secondA kilowatt is 1000 wattsSo, if you multiply Watts * Time = Joules or total energy

consumed.

For example if you have a 100 watt light bulb and leave it on for 24 hours, it will be 100 joules/sec * 86,400 seconds = 8,640,000 joules or 8640 kilojoules.

In terms of kilowatt hours it is 0.1 kw * 24 hours = 2.4 kwh

They are the same measurement.

Features of a CircuitSimple symbols are used to diagram a circuit.

Series Circuits In a series circuit, there is only one path for the current

to take.

In this kind of circuit, if you have one Christmas light go out, then they will all go out.

Parallel CircuitsIn a parallel circuit, there are several paths

for the current to take. So, if one segment is broken, the others take on the extra current.

The multiple wires on this Christmas light keeps it a parallel

circuit so one light burning out does not take out the whole set.

Comparing and ContrastingAs you read, compare and contrast series

circuits and parallel circuits in a Venn diagram like the one below. Write the similarities in the space where the circles overlap and the differences on the left and right sides.

Series Circuit Parallel Circuit

Only one path for current to take

Unbroken path that has a current

Several paths for current to take

Electrical Equipment and Fires

If electrical equipment is not properly used and maintained, it can cause fires. The circle graph shows the percentage of fires caused by different types of electrical equipment.

GroundingOne way to protect people from electric

shock and other electrical danger is to provide an alternate path for electric current.

Fuses and Circuit BreakersIn order to prevent circuits from overheating,

devices called fuses and circuit breakers are added to circuits.

A fuse will break if the current is too high, cutting

off the electricity

Blown FuseWhen the current is too high (like after a lightning

strike), the fuse breaks and the circuit is no longer connected

Circuit Breaker

With a breaker box, when the current gets too high, it switches the switch off, breaking the connection and protecting the electronic devices hooked up to it.