Static Electricity Flashcards
A substance that loses electrons becomes
Positively charged
A substance that gains electrons becomes
Negatively charged
Like charges
Repel
Opposites
Attract
If one is charged and the other is not
They attract
Atomic structure
Nucleus containing protons & neutrons orbited by electrons
When an acetate rod is rubbed with a duster
Electrons are transferred from the rod onto the duster making the rod positively charged. With a polythene rod it works the opposite way
Problems with static
- dust and dirt attracted to charged objects
- hair going static if rubbed with synthetic material
How is an atom electrically neutral?
The number of positive charges carried by the protons in its nucleus is balanced by the number of negative charges on the electrons in the electron ‘cloud’ around the nucleus
Atoms of an element with different numbers of neutrons
Isotopes of the element
Gold leaf electroscope
Detects electric charge - the greater the amount of charge present, the more the gold leaf sticks up
Why would a polythene strip become charged if rubbed with a wool cloth, but not an aluminium strip?
Polythene is an electrical insulator
Aluminium is a metal, and is therefore a conductor
An electric current is a flow of
Electrons and ions
How can you tell if an insulator is charged?
2
If a plastic rod is rubbed with a duster it attract small pieces of paper
When a ballon is rubbed on a jumper it can stick to a wall
How does a spark occur?
If an object is very charged it can force the air to conduct in order to become neutral
Discharging in operating theatres
Oxygen and other gases in operating theatres flow through pipes, causing static charge to build up. The floor is made of conducting materials to allow the charges to escape to earth
Discharging in flour/saw mills
Dust can erupt explosively if there is a spark. Everything is earthed to allow charge to escape
Discharging safely when refuelling planes
Long one!!!
Petrol moving through pipes and planes moving through air both get charged up
The charge can’t escape due to rubber wheels
Any spark could ignite the fuel
The plane and tanker are connected together by a metal rope/chain which also connects to the ground so any charge can escape safely to earth
Current in a series circuit
The current is the same at all points in a series circuit
Voltage in a series circuit
The sum of the voltages across the components = the voltage across the battery
Current in a parallel circuit
- Current splits/joins together at junctions
- current into junction = current out of junction
- on a particular bran h the current is the same everywhere
Direction of electric current in a circuit
From positive to negative
Electron flow
Negative to positive
Current
Rate of flow of charge
Equation for current
Current = charge ➗ time
I Q. t
Equation for voltage (not ohms law)
Voltage = energy ➗ charge
V. =. E. Q
Equation for resistance
Resistance = voltage ➗ current
R. V. I
Resistance measures
‘How hard’ it is for electrons to move round a circuit
Resistance is high
The electrons progress more slowly and current is low
Resistance is low
Electrons progress more quickly and the current is high
A resistor
A component that regulates the currents in a circuit
Why do we put the correct value of resistor into a circuit
To achieve the correct current to operate a particular device
The bigger the resistor
The slower the current
How is lightning formed
4 LONG!!
- within a thundercloud, small bits of ice bump together creating an electrical charge
- the negative charge is usually closest to earth, causing a positive charge to build up on the ground beneath the cloud
- the grounds electrical charge concentrates on anything that sticks up
- the charge streaming from these points eventually connects with the charge reaching down frown the clouds and lightning strikes
Which experiments show that there are two types of electric charge?
Rubbing Acetate & polythene rods with a duster
Demonstrates both attraction & repulsion
Why does your hair stand on end when a van de graaf generator gives you a negative charge
Electrons go from generator to hair
Each hair has -ve charge
Like charges repel
