Electrostatics Flashcards
(38 cards)
What is static electricity?
The build up of charge on an object
What is Coulomb’s first law?
Like charges repel, opposites attract
What happens to electrostatic forces as the charged objects get further apart?
They decrease
What materials conduct charge?
Conductors
What materials don’t conduct charge?
Insulators
What is a static charge?
A charge which builds up in one place and is not free to move
What are the 3 ways to charge an object?
Friction, Induction, Contact/Conduction
How does charging by contact work?
Rub 2 insulators together -> electrons are transferred from one to the other
The direction of transfer depends on materials involved
How does charging by induction work?
- Charged object brought near
- Object grounded (electrons flow in/away)
- Object ungrounded
How do you charge an object without touching it?
Charging by induction
How does charging by contact/conduction work?
Charges spread out inside a conductor or move from one to another
Different to by friction
What are induced charges?
Redistribution of charge in an object due to the presence of a charged object
Which charges move in electrostatics?
Electrons, never protons
Can static charges occur on conductors?
Yes
How can you safely discharge a charged conductor
Ground it
What is voltage
P.D. = Potential Difference
What happens if the p.d. between two objects gets too large
A spark
What charge does a polythene rod acquire when rubbed with a cloth
Negative
What is does a G.L.E. (Gold Leaf Electroscope) do?
It measures the magnetude of the charge on an object
What charge does an acetate rod acquire when rubbed with a cloth?
Positive
How does a G.L.E. work?
- When charged object is brought near metal disk, charges are induced
- This makes the two gold leaves at the bottom the same charge
- They repel with a force proportional to their charge.
How can you test if an object is charged (without using a G.L.E)
- Suspend a rod with known charge on thread (or on watch glass)
- Bring test object near
How is static electricity used in an inkjet printer?
- Droplets of ink are forced out of nozzle (they become charged)
- Pass between metal plates.
- Voltage applied to plates so 1 negative, 1 positive
- By changing size and direction of the voltage across the plates the direction of drops is controlled
How is static electricity used in a photocopier?
- Image of document projected onto positively charged plate
- No charge where light hits plate
- Negative toner particles attracted to charged plate
- Paper placed over plate and toner transferred and heated
