Chapter - 17 (Static electricity) Flashcards
What are the 2 types of charges?
- Positive
- Negative
what happens to opposite charges?
attract
What happens to like charges?
Repel
What is electric charge measured in?
Coulombs (C)
How is electrostatic repulsion caused?
When the charges are the same as reach other (repulsion)
How do insulating solids get a charge?
- by friction to transfer electrons
- by removing electrons that have a negative charge are left with a positive charge
What is the process for producing an electrostatic charge?
- Suspend insulating material using a cradle and a length of string so that the material can rotate softly
- Rub one end of material using a cloth (in order to give it a charge)
- Take a 2nd piece of insulating material and charge that by rubbing with a cloth
- Hold the charged end of the 2nd piece end of First piece
- if the material piece rotates away (repelled) then materials have the same charge
- if the First piece move towards (is attracted) then they have opposite charges
What does a charged object create?
Electric field
How is electric field shown?
Field lines point away from positive charges towards negative charges
What does the direction of force refer to?
A positive charge, it is always electrons that are free to move according to that force.
What does the strength of an electric field depend on?
Distance from the object creating the field.
- field is strongest close to the object (lines are close)
- field is weaker away from the charged object (lines are further away)
What do objects in electric field experience?
Electric field
What do the direction of the force depend on?
Charges are same or opposite
What 2 options can the force be?
- Attractive
- repulsive
What happens to the forces if charges are the same?
- (negative and negative) or (positive and positive)
- repulsive
- 2nd object will move away from the charge creating field
What happens if the charges are opposite?
- (negative and positive)
- Attractive
- object move towards charge creating field
What does the size of force depend om?
Strength of field at that point
What does it mean when the force becomes stronger?
The distance between two charged objects decreases
What does it mean when the force becomes weaker?
distance between 2 charged objects increases
What should we note about the field lines?
Go from positive to negative
Same direction as the direction of the force on a positively charged particle at a point.
What is the electric field between two parallel plates?
uniform electric field.
What are the properties of electric field lines?
- directed from positive to negatuve plate
- parallel
- straight lines
How are field lines around a charged conducting sphere?
- Symmetrical
- they repel (charge same)
- charges on surface will be evenly spread
- surface is conducting allowing them to move
How can the field line be demonstrated?
Van der Graff Generator
How can the field lines be demonstrated in schools?
- small pieces of paper
- polystyrene beads
- aluminum foil containers
What is main difference in conductors and insulators?
Conductors - allow charge carrier to move freely
Insulator - do not allow charge carriers to move
Due to their internal structures.
Define conductor
A material that allows charge (usually electrons to flow through it)
What are examples of conductors
Silver
Copper
aluminum
Steel
What are the conductors made up of?
Positively charged metal ions with their outermost electrons delocalized.
Why do metals conduct electricity?
- current is the rate of flow of charged particles
- more easily the electrons are able to flow, the better the conductor.
Define insulator.
Insulator is a material that has no free charges and does not allow the flow of charges.
What are examples of insulators?
- Rubber
- plastic
- glass
- wood
What can be used to investigate electrical conductors and insulators?
Gold leaf electroscope (GLE)
What does the GLE consist of?
- metal plate attached to one end of metal rod
- other end is a thin leaf of gold foil
- rod held by insulating collar inside a box with glass sides, allowing gold leaf to be seen and protected from draughts
What happens when the GLE is charged?
- plate, rod, and gold leaf have same charge
- they repel and leaf sticks out the side
- when rod and leaf are discharged, (are neutral) the Leafs hang down.
How do we test the electrical conductors and insulators?
- charge the plate of GLE so that gold leaf stands clear of the rod
- carefully touch the plate of GLE with items being tested
What should you do after you test for electrical conductors and insulators?
Record the observation:
- Leaf falls: Material is a good conductor
- Leaf remains in place: Object is poor conductor (good insulator)
- Leaf falls slowly: Material is a poor conductor.
What is an alternate way to test for electrical conductors and insulators?
An electronic charge detector
