GRADE 10 PHYSICAL SCIENCE

CAPS 2018

ROBYN BASSON

TB pg. 101

The study of charges

that do not move.

Charges that are

STATIC or at rest.

Static electricity

consists of electric

charges that build up

on the surface of the

object.

TB pg. 101

Atom:

Protons

Neutrons

Electrons

Neutral (protons = electron's)

A positively charged object

Looses electrons – therefore there is a shortage of electrons

A negatively charged object

Gains electrons – therefore there is

an excess of electrons

There are two types of charge:

Positive Negative

TB pg. 101

Forces that are exerted by charged objects on other

objects are called ELECTROSTATIC FORCES.

Type of forces: Attraction

Repulsion

Like charges repel.

Unlike charges attract.

Unit of charge:Coulomb

Symbol: C

Charge of 1 electron:

− 1.6 × 10−19𝐶1C = 6.25 × 1018 electrons

TB pg. 102-103

Objects are charged by: 1. Friction

2. Contact

3. Induction

1. Friction

• If a glass rod is rubbed with a

woollen cloth, electrons are

physically rubbed off the glass rod

onto the woollen cloth.

• This is how the woollen cloth is given

extra electrons and becomes

negatively charged.

• The glass rod loses electrons and

becomes positively charged. TB pg. 103

Objects are charged by: 1. Friction

2. Contact

3. Induction

2. Contact

• If a charged object touches

an uncharged object, they will share their charges according

to their size.

TB pg. 103-104

Example

An object with a charge of −3.6𝐶 touches an identical neutral object.

During contact, −1.8𝐶 of the objects charge will be transferred to the neutral object and both objects will now have a charge of −1.8𝐶.

Negatively charged object and neutral object:

Electrons will move from negatively charged

object (where there is excess electrons) to

neutral object.

- neutral

TB pg. 104

Example

An object with a charge of +4.8𝐶 touches an identical neutral object.

While in contact, -2.4C will be transferred

from the neutral object to the positive object. Both objects will now have a charge of the same positive charge.

Positively charged object and neutral object:

Electrons will move from the neutral object to the

positively charged object (where there is a shortage

of electrons).

If the objects are identical, the electrons will flow

until they both have the same positive charge.

+ neutral

TB pg. 104

Objects are charged by: 1. Friction

2. Contact

3. Induction

3. Induction

This is the method of charging

whereby the object to be charged does not touch

another charged object.

TB pg. 104

Induction is simply the “moving

around of charges”.

Some molecules, like water, are polar. This means that they have a positive and a negative side due

to the nature of their atoms.

They can thus rotate in the liquid or gaseous state so that their oppositely charged parts are

facing the charged object and hence they are attracted.

TB pg. 104

Conductors have many

delocalized electrons which are free to move

from one side to the

other side.

This will make the one

side temporarily positive and the other side

temporarily negative.

TB pg. 105

An insulator

becomes polarised if the

charges in the

molecule change position slightly.

A conductor

becomes polarised if the

negative charges

in the conductor move.

+-

+-

+-

+-

+-

+-

+-

+-

++

++

+

- - ----- -

TB pg. 105

• A neutral object is still neutral, since it has

the same number of positive and negative charges, but the object

becomes polarized when the charges

are not spread out evenly.

• This polarization is temporary.

neutral neutralTB pg. 105

Materials that can conduct an

electric current.

Metals. Valence electrons are

delocalized and can therefore

move around.

Substances offer very little

resistance to charge.

Materials that cannot conduct an

electric current.

Materials that cannot have a flow

of charge through them.

Non-metals like plastic, Teflon,

porcelain and rubber. TB pg. 107

Only electrons can be added or

removed from an object.

Law of conservation of charge:

Charges cannot be created or

destroyed, only transferred from one

object to another.

The sum of the charges

before contact/transfer is

equal to the sum of the

charges after the

contact/transfer.

TB pg. 106

The net

charge of an

isolated system

remains

constant during any

physical

process.

-3.6C

• Two identical charged objects of -3.6C and

+4.8C touch each other and are then separated.

• Calculate the charge on each of the objects.

TB pg. 106

+4.8C

Formula is NB!

The charge that is transferred from one object

to another is carried by electrons.

The charge of an electron is −1.6 × 10−19𝐶.

This means that the charge that is transferred

must be a multiple of the charge of an

electron.

This principle is known as the quantifying of

charge.

-6C +8C

Every charge in the universe

consists of integer multiples of

the electron charge.

𝑄 = 𝑛𝑞𝑒

Charge of object

Whole number

(number of electrons)

Charge of one

electron (−1.6 × 10−19𝐶)

• How many electrons are transferred

if an object has a charge of

7.5 × 10−9𝐶?

Riley, the dog, walks around with

5.23 × 108 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠. How much charge is he carrying around?

Name 2 types

of charges

Give 3

examples of

conductors

Give 3

examples of

insulators

How are objects

charged?

When is an atom

electrically

neutral?

A positive charge

is formed when…

A negative charge

is formed when…

+ neutral ? ?+ +

+ + ? ?+ +

- - ? ?- -

Exercise 10 pg. 108-109

The electrical force between two charged

objects is directly proportional to the product of

the charges and inversely proportional to the square of the distances between them

𝐹 =𝑘𝑄1𝑄2𝑟2

vector

Force (N)Charge

(C)

distance (m)Electrostatic constant

(9 × 109𝑁𝑚2/𝐶2)

𝟏𝒎𝑪 = 𝟏 × 𝟏𝟎−𝟑𝑪𝟏𝝁𝑪 = 𝟏 × 𝟏𝟎−𝟔𝑪𝟏𝜼𝑪 = 𝟏 × 𝟏𝟎−𝟗𝑪𝟏𝒑𝑪 = 𝟏 × 𝟏𝟎−𝟏𝟐𝑪

Find the force between the charges of + 10𝜇𝐶 and −50𝜇𝐶 located 20cm apart.

Worksheet