Topic 1 - Static and Current Electricity Flashcards
What is contained in the nucleus of an atom?
Protons and neutrons
What is the overall charge of a nucleus?
Positive
What gives an atom its overall size?
Electrons whizzing around the outside
What is the relative mass of a proton?
1
What is the relative charge of a proton?
+1
What is the relative mass of a neutron?
1
What is the relative charge of a neutron?
0
What is the relative mass of an electron?
1/2000
What is the relative charge of an electron?
-1
What causes the build up of static electicity?
- When 2 insulating materials rubbed together, electrons are transferred from one to the other
- Positive static charge on one and negative charge on other
- Only electrons move, not protons
- Charges are equal + opposite
What happens when a polythene rod and a cloth are rubbed together?
- Electrons move from the cloth to the rod
- Rod becomes negatively charged + cloth has equal positive charge
What happens when an acetate rod and a cloth are rubbed together?
- Electrons transfer from the rod to cloth
- Cloth ahs negative charge + rod has equal positive charge
What happens when two objects have the same charge?
- Repel from each other as same charges repel
- Electrostatic forces of attraction
What happens when two objects the different charges?
- Attract together as opposite charges attract
- Electrostatic forces of attraction
How does static electricity cause clothes to crackle?
- When synthetic clothes dragged over each other (e.g. in tumble drier), electrons transfer, leaving static charges on both
- Attraction between items + little spark as charges rearrange themselves
How does static electricity cause car shocks?
- Static charge builds up between clothes + synthetic car seat; friction causes electrons to transfer
- When get out of car + touch metal door, charge flows giving a shock
- Some cars have conducting strips that hang behind car giving a safe discharge to earth
How does static electricity cause shocks from door handles?
- Walk on nylon carpet wearing shoes w/ insulating soles
- Electrons transfer from carpet to you so charge build up on body
- If touch metal door handle, charge flows to conductor giving a shock
How can a balloon be made to stick to a wall?
- Rub balloon against hair/clothes, so electrons transfer to balloon (giving it a negative charge)
- Sticks to wall although wall isn’t charged
- Charge on surface of wall moves a bit: negative charge repels so positive charge is on wall surface, attracting balloon, holding balloon to wall
- This is called induction
How can a comb be charged to pick up small pieces of paper?
- Run comb through hair, so electrons transfer to comb so it’s negatively charged
- Picks up paper although paper has no charge
- Negative repels so positive on top sticking to comb
- Induction
What causes lightning?
- Static charge
- Rain drops + ice rub together inside storm clouds
- Electrons transfer
- Positive charged on top and negatively charged on bottom
- Creates a voltage + spark as wants to get earthed
How do paint sprayers use electrostatic charges to get an even coat on bikes and cars?
- Spray gun charged, charging small drops of paint
- Drops repel others as same charge, so get fine spray
- Object given opposite charge to gun, attracting fine spray of paint
- Method gives even coat + hardly any paint wasted
- Parts facing away from the gun still get painted; no shadows
- Same as how insecticides sprayers work
How are electrostatic charges problematic when fuel filling and how can this be resolved?
- As fuel flows out filler pipe, static builds up
- Can easily lead to spark which can cause explosion
- Sparks prevented by being earthed
How does earthing stop electrostatic charges building up?
- Dangerous sparks can be prevented by connected charged object to ground by conductor (earthing)
- Provides easy route for static charges to travel into ground so no charge can build up to shock or spark
- Electrons flow down conductor to ground if charge negative + flow up conductor from ground if charge positive
Why must fuel tankers be earthed?
To prevent any sparks that might cause the fuel to explode
What is current?
Rate of flow of charge around a circuit
In the metal wires of a circuit, what is charge carried by?
Electrons
Why are metals good conductors?
Have free electrons that are free to move
What causes charge to build up?
When current flows past a point in a circuit for a certain length of time
What is the formula for charge?
Charge = current x time
Q=It
What is charge measured in?
Coulombs
What is current measured in?
Amperes
How does a bigger current affect the charge?
More charge
What type of current do cells and batteries provide?
Direct current (d.c.)
What is direct current?
Current that keep flowing in the same direction
What does a direct current look like on an oscilloscope?
Always has same voltage so is just a straight line
What type of current is mains electricity?
Alternating current - constantly changing direction
