Chapter 7: Electric

7.1 Analysing electric fields and charge flow

What are atoms?

Matter is made up of tiny particles called atoms

An atom consists of..

• Center of atom– Nucleus• Protons : Positive charged• Neutrons : Neutral / uncharged• Electrons surround : negative

++

+ ++

+

--

--

--

Nucleus

Neutrons

Protons

Electrons

Neutral charged

Positive charged

Negative charged

+

-

Electric charge:

Symbol: QUnit: Coulomb

C

One ProtonElectron

1.6 x 10-19 C-1.6 x 10-19 C

Charge

A body is:

- +NNegatively Charged Neutral Positively Charged

+++-

-

--

-- ++

+ ++

+

--

--

-- ++

+ ++

+

-

-

-

More negative charge than positive

Equal negative and positive charge

More positive charge than

negative

Forces acting on two bodies:

Same Net Charges

Different Net Charges

The force causes movement of electrons or flow of charges

- - + +Repel

- -++Attract

Electric Current

Current

I =Q

t

Charge

Time

SI Unit: Ampere

A

Electric FieldAn electric field is a region in which an electric charge experiences an electric force (attraction or repulsion)

Created from a positively charged sphere in the spaces surrounding it

Electric Field

+A negative charged body when placed at any point in this region is pulled towards the charged sphere

-AttractiveForce

Represented by series of arrowed linesElectric Field

+ -Electric field lines

Electric Field Linesindicate both:

Magnitude

Direction of the field

Direction of the force acting on a charged body placed at that point

+

-

Never cross each otherElectric Field Lines

+WRONG

+CORRECT

Electric field lines are most dense around objects with greatest amount of charge

Electric Field Lines

+Less DenseLess Charge

More DenseMore Charge

+

Photo credits

• Flickr/magnifier test coil/tesla1000• Flickr/phenomena/amsterdam today• Flickr/I hope mom doesn’t see

this/tayyywilson• Flickr/rural electricity/kevin dooley• Flickr/green wheat/bernat casero