Unit 5 notes

(1)

Unit 6 -

Electricity

Unit 6 -

Electricity

Electric Charge

 _{Static Electricity}  _Conductors

(2)

Static Electricity

 _{Static Electricity}

 _{the net accumulation of electric charges}

on an object

 Electric Field

 force exerted by an e- on anything that

has an electric charge

 opposite charges attract

(3)

Static Electricity

 _{Electricity can be transferred}  _{By friction}

• Rubbing two surfaces together – Walking across carpet

 By contact

• From one object to another – Van der Graaff generator

 By induction

(4)

Static Electricity

 _{Static Discharge}  _{the movement of}

(5)

Conductors

 _Conductor

 _{material that allows electrons to move}

through it easily

 e- are loosely held

(6)

Insulators

 _Insulator

 _{material that doesn’t allow electrons to}

move through it easily

 _e- are tightly held

(7)

Current

 _Circuit

 _{Potential Difference}  _Current

(8)

Circuit

 _Circuit

 _{closed path through}

(9)

Potential Difference

 _{Potential Difference}_(voltage)

 _{difference in electrical potential}

between two places

 _{large separation of charge creates high}

voltage

 _{the “push” that causes e}- to move from

- to +

(10)

Current

 _Current

 _{flow of electrons through a conductor}  _{depends on # of e}- passing a point in a

given time

(11)

 _Current

 _{Two types:}

• AC (alternating) – charge reverses – common in household circuits

• DC (direct) – charge is one way – common in battery-powered

circuits

Current

(12)

Electric Effects

Effect of Current on the Human Body

Current (mA) Effect

1 Slight tingling sensation

5 Slight shock

6-30 Painful shock; loss of muscular control

50-150 Extreme pain, severe muscular contract. Breathing stops temporarily.

1000-4300 Nerve damage. Death is likely.

(13)

Resistance

 _Resistance

 _{Opposition to the flow of electrons}  _{electrical energy is converted to}

thermal energy & light

 _{measured in ohms (}₎

(14)

Electrical Circuits

 _{Circuit components}  _{Series circuits}

 _{Parallel circuits}

(15)

Circuit Components

A – Battery B – Switch

C – Light bulb D – Resistor

(16)

-Series Circuits

Series Circuits

 _{Series Circuit}

 _{current travels in a single path}

• one break stops the flow of current

 _{current is the same throughout circuit}

• lights are equal brightness

 _{each device receives a fraction of the total voltage}

(17)

Parallel Circuits

 _{Parallel Circuits}

 _{current travels in multiple paths}

• one break doesn’t stop flow

 _{current varies in different branches}

• takes path of least resistance

 _{each device receives the total voltage}

(18)

Household Circuits

 _{Combination of parallel circuits}

 _{every device receives total voltage}

 _{too many devices can cause wires to}

overheat

 _{Safety Features:}

 _{fuse - metal melts, breaking circuit}

 _{circuit breaker - bimetallic strip bends}

when hot, breaking circuit

 _{GCFI – special outlet that monitors}

(19)

Ohm’s Law

 _{Ohm’s Law}

V = I × R

V: potential

difference (V)

I: current (A)

R: resistance (



)

• _{Voltage increases when current increases.}

• Voltage increases when resistance decreases.

I

V

(20)

Ohm’s Law

 _{A lightbulb with a resistance of 160}_is

plugged into a 120-V outlet. What is the current flowing through the bulb?

GIVEN:

R = 160



V = 120 V

I = ?

WORK

:

I = V ÷ R

I = (120 V) ÷ (160



)

I = 0.75 A

I

V

(21)

Measuring Electricity

(22)

Electrical Power

Electrical Power

 rate at which electrical energy is converted to another form of energy

P = I × V

P: power (W)

I: current (A)

V: potential

(23)

Electrical Power

 A calculator has a 0.01-A current flowing through it. It operates with a potential difference of 9 V. How much power does it use?

GIVEN:

I = 0.01 A

V = 9 V

P = ?

WORK

:

P = I · V

P = (0.01 A) (9 V)

P = 0.09 W

I

P

(24)

Electrical Energy

Electrical Energy

 energy use of an appliance depends on power required and time used

E = P × t

E: energy (kWh)

P: power (kW)

(25)

Magnetism

Characteristics of Magnets

 _Magnetism

 _{Magnetic poles}  _{Magnetic field}

(26)

Magnetism

 _Magnetism

 _{force of attraction or repulsion}

between unlike or like poles

 _{due to the arrangement of electrons}

(27)

Magnetic Poles

 _{Magnetic Poles}  _{like poles repel}

 _{unlike poles attract}

(28)

Magnetic Field

 _{Magnetic Field}

 _{area around a magnet where magnetic}

forces act

(29)

Magnetic Domain

 _{Magnetic Domain}

 _{groups of atoms with aligned magnetic}

poles

 _{in a magnetized object, domains are all} aligned

(30)

Uses of Magnetic Fields

 _{Electromagnet}  _Speaker

(31)

Electromagnet

 _{Electromagnet}

 _{strong, temporary magnet formed when}

current is passed through a coil of wire surrounding an iron core

 _{more coils of wire, stronger magnet}

(32)

Speaker

 _Speaker

 electrical energy  mechanical energy

 _{wire coil moves back &}

forth as its magnetic field interacts with the field of a fixed magnet

 _{forced vibration causes}

(33)

Motor

 _Motor

 electrical energy  mechanical energy

 _{electromagnet}

rotates between

the poles of a fixed magnet

 _commutator

(34)

Motor

brushes & wires to battery field magnet

(35)

Producing Electric Current

 _{Electromagnetic Induction}  _{Electric Generator}

 _{AC & DC}

(36)

Electromagnetic Induction

 _{Electromagnetic Induction}

 producing a current by moving a wire through a magnetic field

 _{some microphones}

work just like mini-speakers in reverse

 _{sound waves cause}

coil to move  current

Dynamic Microphone

(37)

Electric Generator

 _{Electric Generator}

 mechanical energy  electrical energy

 _{armature is}

rotated between magnet poles

 _{magnetic field}

induces a current in the wire coil

MOTOR

(38)

Electric Generator

 _{Hydroelectric Dam}

 _{PE of lake water is} converted to KE

 _{mechanical KE}

(39)

DC & AC

 _{Direct Current (DC)}

 _{current flows in one direction}  _{dry cells}

 _{Alternating Current (AC)}

 _{current reverses its direction} at regular intervals

(40)

Transformer

 _Transformer

 increases or decreases AC voltage

 primary coil AC produces a magnetic field that induces AC in the secondary coil

(41)

Transformer

 _{Step-up Transformer}

 increases the voltage

 more turns

 power plants

 _{Step-down Transformer}

 _{decreases the voltage}  _{fewer turns}

 _{household appliances}