Chapter 16
LESSON OBJECTIVES
At the end of the lesson, you should be able to:
•State that there are positive and negative
charges and that charge is measured in
Coulombs.
•State that unlike charges attract and like
charges repel.
•Show
understanding
that
electrostatic
charging by rubbing involves a transfer of
electrons.
ELECTROSTATICS
• Electrostatics is the study of static (non-moving)
electric charges.
Prior Knowledge from Secondary 2
•All matter is made of up atoms, which consist of (1) a nucleus (containing protons and neutrons)
ELECTROSTATICS
• Which is the proton?
• Which is the neutron?
• Which is the electron?
• What are the charges of the sub-atomic
ELECTROSTATICS
• Protons are positively charged and electrons
are negatively charged.
• In an electrically neutral atom, the number of protons and electrons are equal.
• Electrons can be removed from the atoms or
ELECTROSTATICS
• The study of these net stationary charges and their effects on each other constitutes the subject of electrostatics or static electricity.
Do you know ????
Electrostatic Charging BY Friction
• Some objects can obtain electric charges when they are rubbed together.
• Friction transfers negative charges (electrons) from one object to another.
Electrostatic Charging BY Friction
Electrostatic Charging BY Friction
Electrostatic Charging BY Friction
Example : Rubbing silk with glass rod
neutral
neutral Positively Charged
Negatively Charged
When a glass rod and a piece of silk are rubbed together, the atoms at the surfaces
are disturbed. This causes some electrons
Electrostatic Charging BY Friction
The table below gives types of charges acquired when some materials are rubbed together.Electrostatic Charging BY Friction
• There are two types of charges – positive and
negative.
• When two objects have the same charge, they will repel each other.
Electrostatic Charging BY Friction
Question:-What is a neutral object? Will a neutral
object be attracted or repelled by a
charged object?
•
Neutral objects have equal amount of
positive and negative charges
•
The
neutral
object
will
still
be
MEASUREMENT OF ELECTRIC CHARGE
• Electric charge is measured in coulombs (C).
This is the SI unit of electric charge.
• The charge of an electron or proton is :
• Charge of electron : -1.6 × 10-19 C
• Charge of proton : 1.6 × 10-19 C
MEASUREMENT OF ELECTRIC CHARGE
For practical reasons, we can use submultiples of couloumbs, ie,
• 1 millicoulombs (1mC) = 10-3 C.
• 1 microcoulombs (1µC) = 10-6 C.
INSULATORS
&
Insulators & Conductors
• During charging, electrons are transferred from one material to another. These electrons that are transferred are unable to move freely within the new materials.
• These electrons remain at the surface where the material has been rubbed.
Insulators & Conductors
• Electrical conductors are materials where electrons are free to move about within them.
• Electrical conductors can conduct electricity
and they are charged by induction.
CHARGING BY INDUCTION
• Induction is process of charging a conductor without any contact with the charging object.
EXPERIMENT : CHARGING BY INDUCTION
(TEXTBOOK PAGE 310)
Two conductors (metal spheres) on insulating stands are placed touching each other.
-EXPERIMENT : CHARGING BY INDUCTION
(TEXTBOOK PAGE 310)
A negatively charged rod is brought near one of the sphere (A). This causes the electrons in the metal spheres to be repelled to the far end of sphere B.
EXPERIMENT : CHARGING BY INDUCTION
(TEXTBOOK PAGE 310)
EXPERIMENT : CHARGING BY INDUCTION
(TEXTBOOK PAGE 310)
EXPERIMENT : CHARGING BY INDUCTION
(TEXTBOOK PAGE 310)
Bring a positively charged glass rod near the metal conductor on an insulating stand.
The free electrons in the metal will be drawn towards the side nearer the positively charged glass rod.
EXPERIMENT : CHARGING BY INDUCTION
(TEXTBOOK PAGE 310)
Without removing the glass rod, earth the positively charged side of the metal conductor by touching it with your hand. The human body is a relatively good conductor and will allow electrons to flow into the conductor from the ground.
EXPERIMENT : CHARGING BY INDUCTION
(TEXTBOOK PAGE 310)
EXPERIMENT : CHARGING BY INDUCTION
(TEXTBOOK PAGE 310)
NEUTRALISING CHARGED
INSULATORS AND CONDUCTORS
DISCHARGING A CHARGED
INSULATOR
• An effective way of discharging a charged insulator is by heating.
• The intense heat causes the air surrounding the charged insulator to be ionized.
DISCHARGING A CHARGED
INSULATOR
• Humid conditions will also neutralize a charged insulator over a period of time.
DISCHARGING A CHARGED
CONDUCTOR
• A charged conductor can be neutralised by earthing it.
• To earth a charged conductor is to provide a path for the excess electrons to flow away or for electrons to flow to the conductor.
LESSON OBJECTIVES
At the end of the lesson, you should be
able to:
•Describe an electric field as a region in
which an electric charge experiences a force
•Draw the electric field of an isolated point
charge and recall that the direction of the
field lines gives the direction of the force
acting on a positive test charge.
ELECTRIC FIELD
An electric field is a region where an electric
charge experiences an electric force.
ELECTRIC FIELD
ELECTRIC FIELD
We can represent the area where the charges experienced electric forces by drawing electric field.
We use solid lines with arrows to represent the electric fields. These lines are called the
electric line of force.
ELECTRIC FIELD
ELECTRIC FIELD
ELECTRIC FIELD
HOCKEY APPLET
ELECTRIC FIELD
Worked Example
ELECTRIC FIELD
(a) Explain why the sphere moves immediately to the new position.
ELECTRIC FIELD
(a) Explain why the sphere moves immediately to the new position.
ELECTRIC FIELD
(b) How does the movement of the ball illustrate the meaning of the term electric field?
HAZARDS AND
APPLICATIONS
OF
Some hazards of electrostatics
•
Lightning
The flashes of lightning are due to the discharge of a large quantity of electric charge built up in the thunderstorms.
When the charge in the
Some hazards of electrostatics
•
Electrostatic discharge
Excessive charges may build up between objects due to friction.
PRACTICAL APPLICATIONS OF
ELECTROSTATICS
•
Photocopier (Read Page 316)
•
Electrostatic precipitator (Read Page
317)
•
Spray painting (Read Page 317)
•
Crop sprayers (Read Page 317)
