Electricity

Originally called the electrical effect!

Discovered aproximately 2700

years ago!“Electrical” come

from the greek word Elektron, meaning

Amber

Amber was found to attract objects after it

was rubbed against wool

Electrical charge

• To better understand electricity we must look at the atomic model.

-

-

-

+ ++Protons

Neutrons

Electrons

Electrical charge

• Electrical charge comes from the protons and electrons of an atom. The protons carry the positive charge, while the electron carries the negative charge.

• Negatively charged bodies carry more Electrons then Protons

• Positively charged bodies carry more Protons then Electrons

Electrons can be removed from atoms – Positive: electrons are stripped off– Negative: extra electrons are added

Electrical charge• Electrical charge is measured in Coulombs

(repressented by the symbol q )• 1 Coulomb is equal to the electrical charge of a

single Electron. 1 Electron carries a charge of 1.602 x 10 -19 C

• Identifying electrical charges has allowed scientists to discover:– Opposite charges attract each other(+ and -)– Like charges repel each other (+ and +, or – and -)

This is refered to as the “Forces of attraction and Repulsion”

Electrical charges

• An object is charged when an imbalance is created in the electrical charge of that object

• When an object is charged the charge is spread evenly across the surface while the interior remains neutral.

Conductors and Insulators

• Objects can be classified into three categories depending on how they react to receiving electrical charges.– If the substance allows the flow of electrical charge

it is considered a conductor– If the substance stops the flow of electrical charge it

is considered an insulator– If the substance slows the flow of electrical charge

or has varying conductivity it is considered a semiconductor

Electrical charge

Open your text books to pages 140 – 143 and complete the handout #19

Electrical Field • The electrical field of an object is the area in

which the electrical charge of one object can act on another charged object.

Static Electricity

• Electrostatic electricity deals with the electrical phenomena related to insulated charges which are generally at rest.

The word static comes from the greek word

Statikos, meaning “causing to stand

Static electricity

• Electroscopes can be used to detect static electricity.

Charging an object

• There are three ways to charge an object• Friction• Conduction• Induction

Charging via Friction• Rubbing two neutral bodies together often

results in the transfer of electrons, creating two oppositely charged bodies.

Plastic

Sulfur

Gold

Nickel, Copper

Hard Rubber(ebonite(bow

ling balls))

Wood, Yellow

Amber, Resin

Cotton

Paper

Silk

Lead

Wool

Glass

Tendency to acquire a

negative charge

(-)

Tendency to acquire a

Positive charge

(+)

Charging via conductionWhen an insulatd neutral object comes into contact

with an object with an excess charge, the two object can share the charge, resulting in two weaker charges

Charging via InductionWhen a neutral object is approached with an object

with an excess charge, the neutral object can achieve an unbalanced charge provided it is not insulated .

Electrical charge

Open your text books to pages 145 – 148 and complete the handout #19

Dynamic Electricity

• Dynamic means electricity in motion

• Static electricity refers to electrons moving about at random

• Electrical current is the orderly flow of negative charges carried by electrons

Electric current is analogous to water flow. Which elements correspond in the two systems?

Electric Current: Flow of Charges

Electric Current and Water Flow

Electrical Current• Current Intensity– Measured in Amperes(amps)• Refers to how much charge passes a given point every

second• 1 amp = 1 coulomb of charge every second

– Current intensity can be determined by the the following equation

I=q/ΔtI = current intensity(amps)

q = charge(coulombs)Δt = time(sec)

Practice

• If 300 c pas through a circuit in 2 seconds what is the current intensity?

150 A• If a light needs 3 amps worth of current to work for

1 minute what charge is require?180 C

• If the projector requires 5 amps worth of current and is supplied with 400 c how long could it run for?

80 seconds

Electric CircuitsElectric circuit–Unbroken path of material carrying

electricity– Electrical conductor

Circuit– A source of energy (battery)– A loop of wire– A device to use the electrical energy

Potential difference

The amount of energy transferred between two points in a circuit (volts)

Calculated using the following formulaV=E/q

V = Potential difference(volts)E = Energy transferred (Joules)

q = charge (Coulombs)

Practice

• The circuits in the school wall have a potential difference of 120 V. How much energy is provided by a charge of 300 c?

360 00 J• If a cars internal circuits receive 400 00 J from

a charge of 125 c what is the potential difference of the circuit?

320 V

Resistance• Refers to the ability of a material to slow the flow of electrical

current. Measured in Ohms (Ω)• See P 153 of your text for table 5.22 which explains the

different factors affecting the resistance of a substance to current flow.

Ohm’s Law

V=RIV= Potential difference (Volts)

R = Resistance (Ohms)I = current intensity (Amps)

For any resistance(Ω) the potential difference(V) is proportional to the current intensity (A)

Practice

• What is the resistance of a circuit with a potential difference of 200 V and a current intensity of 10 A?

20Ω• What is the current intensity of a circuit with a

resistance of 15Ω and a potential difference of 30 V?

2 A

Electrical powerHow much energy a device can transform, or the

amount of work it can perform.Measured in Watts(W)

Watts are a function of energy over time;1W = 1J/1S

Electrical power is calculated using the followingPe = W/Δt

Pe = Watts(electrical power)W = Work(J)Δt = time(s)

Power and Electrical Energy

Types of Circuits

• Series circuits• Parallel Circuits

Pe = W/Δt or Pe = V/I Pe = Watts(electrical power)

W = Work(J)Δt = time(s)

V = Potential difference(volts)I = current intensity (Amps)

V=RIV= Potential difference (Volts)

R = Resistance (Ohms)I = current intensity (Amps)

V=E/qV = Potential difference(volts)E = Energy transferred (Joules)

q = charge (Coulombs)

I=q/ΔtI = current intensity(amps)

q = charge(coulombs)Δt = time(sec)