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Chapter 22 Current Electricity. 22.1 Current & Circuits. Electricity did not become an integral Part of our daily lives until Scientists learned to control the Movement of electric charge. This is known as current. Electric currents are responsible For many things; computers,

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Presentation Transcript
slide1

Chapter 22

Current Electricity

slide2

22.1 Current & Circuits

Electricity did not become an integral

Part of our daily lives until

Scientists learned to control the

Movement of electric charge.

This is known as current

slide3

Electric currents are responsible

For many things; computers,

Cars, and every move you make.

Current is the rate at which

Electric charges move through

A given area.

slide4

Conventional current is defined

In terms of positive movement.

Electricity is the movement of

Electrons, the negative charge,

Moving in a direction. This direction

Is in the positive direction.

slide5

Solutions that have dissolved

Ions can be charge carriers,

These are called electrolytes.

Drift velocity is the net velocity

of a charge carrier moving in

An electric field.

slide6

Drift speeds are relatively small.

The speed of an electron in a

Copper wire is only about

0.000246 m/s! The electric

Field, on the other hand, is

Almost the speed of light.

slide7

Batteries and generators

Supply energy to charge carriers.

Both batteries and generators

Contain a potential difference

(volts) across their terminals.

Batteries use chemical energy

And generators use mechanical

Energy.

slide8

Current can be direct or alternating.

In Direct Current (DC) the charge

Moves only one way through the

Wire. (like my electric truck)

In Alternating Current (AC), the

Charges are constantly changing,

Creating no real movement of

Electrons.

Our house current in the US is

60 Hz.

slide9

Q

t

I =

I = electric current

Q = charge through a given area

t = time

slide10

The SI unit for current is the

Ampere (A).

The SI unit for charge is the

Coulomb (C).

So the Ampere is 1 C per second.

slide11

PROBLEM...

The amount of charge that passes

Through the filament of a

Certain light bulb in 2 s if

1.67 C. Determine the current in

The light bulb.

I = 0.835 A

slide12

There are insulators and

Conductors, but there are also

Not so good conductors.

The impedance of the motion of

Charge through a conductor

Is the conductor’s resistance.

Resistance is the ratio of the

Potential difference across

A conductor to the current

It carries.

slide13

V

I

R =

SI unit for resistance is the Ohm,

And is represented by Ω.

slide14

Ohm’s law states that the

Resistance is constant over a

Wide range of applied

Potential differences.

It is usually shown by…

V = IR

slide15

Resistance depends on length,

Cross-sectional area, material,

And temperature.

Resistors can be used to control

The amount of current

In a conductor.

slide16

PROBLEM...

The plate on an iron states that

The current in the iron is 6.4 A

When the iron is connected across

A potential difference of 120V.

What is the resistance of the iron?

R = 19 Ω

slide17

Electric power is the rate of

Conversion of electrical energy.

P = IV

The SI unit is the Watt.

slide18

PROBLEM...

An electric space heater is

Connected to a 120 V outlet. The

Heater dissipates 3.5 kW of power

In the form of heat. Calculate

The resistance of the heater.

R = 4.1 Ω

slide19

An electric circuit is a

Continuous path through which

Electric charges can flow.

There are two types of circuit

Connections,

Parallel & Series

slide20

A parallel circuit is one with

Several current paths, whose

Total current equals the sum of the

Currents in its branches.

slide21

A series circuit is one in which

Current passes through one

Device and then another.

slide23

22.2 Using Electrical Energy

Electric companies measure

Energy consumption in

Kilowatt-hours.

1 kW h = 3.6 X 106 J

slide24

Electrical energy is transferred at

High potential differences to

Minimize loss. (up to 1000000 V)

When the wires are strung, they are

Very tight and straight, they bow

Because they are soooo hot!

slide25

PROBLEM...

How much does it cost to operate

A 100 W light bulb for 24 hours

If electrical energy costs $0.08

Per kW h? What is the cost per

Year? What is the cost if you used

A energy conserving bulb at 14 W?

Cost = $0.19/day $69/year

Cost = $ 0.03/day $9.81/year

slide26

Current moving through a resistor

Causes it to heat up because

Flowing electrons bump into the

Atoms in the resistor.

These collisions increase the

Atoms’ kinetic energy and, thus,

The temperature of the resistor.

slide27

If we rearrange Ohm’s Law, and

The formula for power, we have

3 new formulas that we can use…

And for the thermal

Energy dissipated…

P = I2R

V2

R

P =

V2

R

E =

t

slide28

PROBLEM...

A heater has a resistance of

10 Ω. It operates on 120 V.

What is the power dissipated by

The heater? What is the thermal

Energy supplied by the heater

In 10 s?

1.44 kW 14.4 kJ