# Electric current and

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15 Νοε 2013 (πριν από 5 χρόνια και 3 μήνες)

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Electric current and
electrical energy

Electrical energy

is the energy of electric charges
.

Electric current

(
I
) is the rate at which charges
pass a given point
.
It is measured in
amperes (A)
.

Electric charges flow from an area of high voltage to an
area of low voltage.

The higher the current, the greater the number of
charges that pass a point each second.

How

charges

move

in

the

current?

When there is an electric field in a wire,
free electrons will move. The energy of
each electron is transferred instantly to the
next electron.

Electric current

Direct Current

Alternating
Current

Voltage (V)

Is

the

potential

difference

between

two

points

in

a

circuit
.

Its

unit

is

Volt

(v)
.

It

is

a

measure

of

how

much

work

is

needed

to

move

a

charge

between

two

points
.

It is the amount of energy released as a charge moves
between two points in the path of a current. The
higher the voltage, the more energy is released per
charge, and so, the greater the current is.

Resistance (
R
):

Is the opposition to the flow of electric
current by a material or device. It is
expressed in ohms (
Ω
).

So, it is a type of
electrical friction.

The higher the resistance is, the lower the
current in the material.

Resistance depends on four factors:

1.
Material

2.
Thickness

3.
Length

4.
Temperature

1. Material and Resistance

Good

conductors

Low

resistance

*

Used

to

make

wires

Poor

conductors

High

resistance

2. Resistance, Thickness and Length

Thickness

increases

Low

resistance

Shorter

length

Low

resistance

3. Resistance and temperature

Temperature

increases

High resistance, because the atoms
move faster at high temperatures

Cooling a material to
very low temperature

Resistance

drops

to

0

Ω

Superconductors

Generating electrical energy

Energy

cannot

be

created

or

destroyed
.

It

can

only

be

changed

into

other

kinds

of

energy
.

Generators

convert

mechanical

energy

into

electrical

energy
.

Cell

is a device that changes chemical or
radiant energy into electrical energy and so,
produces electricity.

Parts of a Cell:

1.
Electrolyte
:

A

liquid

that

allows

charges

to

flow
.

2.
Pair of electrodes:
(Enter or exit of charges).

Chemical energy
Electrical energy

Do we use

electrolytes in our
bodies? How?

Kinds of Cells:

A. Dry cells:
electrolytes are solid or
pastelike
.

Example is battery in flashlights.

B
.

Wet

cells
:

electrolytes

are

liquid
.

Example

is

car

battery
.

Thermocouple

It

is

a

device

that

converts

thermal

energy

into

electrical

energy
.

The greater the temperature difference, the greater
the current is.

Photocell

is

a

device

that

converts

light

energy

into

electrical

energy
.

They contain silicon atoms.