Current Electricity Flashcards
(34 cards)
What are the charges on protons,neutrons and electrons?
A proton is positively charged
An electron has an equal negative charge
A neutron is uncharged
What effect does adding or removing electrons have to an uncharged atom?
Adding electrons to an uncharged atom makes it negative( more of the negative electrons than protons)
Removing electrons from an uncharged atom makes it positive( fewer electrons than protons).
Only electrons can be removed/added this is because protons and neutrons are stuck in the nucleus, kept in place by the strong nuclear force.
What happens if 2 insulating materials are rubbed together?
Electrons are scraped off one and dumped on the insulators, which becomes negatively charged.
The electrons try to repel each other but they can’t move apart because their positions are fixed. The patch of charge that results is static electricity.
What happens if a polythene rod is rubbed with a duster(cloth)?
Electrons move from duster to the rod, so the rod becomes negatively charged
What happens if an acetate rod is rubbed with a cloth duster?
Electrons move from the rod to the duster so the rod becomes positively charged
What are the static electricity rules?
Two objects with opposite electric charges are attracted to each other
Same electric charges they will repel
Why do some people’s hair stand on end?
Static builds up hair, giving each strand the same charge-so they repel each other
How do dust precipitators work?
They use static electricity to clean up emissions from factories.
Dust particles become negatively charged as they pass a wire grid in the chimney. The negatively charged dust particles then get stuck to the earthed metal plates and eventually fall to the bottom of the chimney where they can be removed.
How are bikes and cars painted using electrostatic paint sprayers?
The spray gun is charged, which charges up the small drops of paint as well. Each paint drop repels all the others( since they’ve all got the same charge).The object to be painted is given an opposite charge to the gun, so it attracts the fine spray of paint.
How do you prevent sparks occurring?
By earthing a charged object( connecting it to the ground using a conductor) which provides an easy to route for the static charges to travel into the ground.
What is a current?
Rate of flow of charge, measured in amps
What is the potential difference?
The amount of energy transferred per coulomb of charge, passing between 2 points in a circuit, measured in V. It is the ‘driving force’ force that pushes the current round.
What is resistance?
This is any component in the circuit which slows the flow down.
The greater the resistance across component the smaller the current that flows(for a given pd across the components).
Measured in ohms
What is the function of a volt meter?
It measures potential difference between 2 points.
It must be placed in parallel around the component under test.
What is the function of a battery?
A battery transfers energy to the charge as it passes- that’s the ‘push’ force that moves the charge round the circuit.
Why is a voltmeter placed parallel with a component?
So it can compare the energy the charge has before and after passing through the component
The more charge passing through a current…
The greater the flow
When would you use a ‘ standard test circuit’?
If you want to know the resistance of a component(measuring current through and potential difference across).
What is the function of an ammeter?
Measures the current flowing through the component
This must be placed in series( placed anywhere in series in main circuit , but never parallel)
What is the job of the variable resistor?
As you vary the variable resistor it alters the current flowing through the circuit.
This allows you to take several pairs of readings from the ammeter and the current.
What is the relationship between the current and potential difference in different resistors?
( V-I) graphs
( at constant temperature)
The current through a resistor is directly proportional to P.D.
In graph form it’s a straight line through the origin.
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What can you say of the effect of increasing temperature in a filament lamp?
As the temperature of the filament increases the resistance increases.
In graph form you would see a curve.
Describe the current flow in a diode.
Current only flows through a diode in one direction. The diode has a very high resistance in the opposite direction.
Why does resistance increase with temperature( in terms of ions and particles)?
When an electrical charge flows through a resistor, some of the electrical energy is transferred to heat energy.
This heat energy causes the ions in the conductor to vibrate more.
With the vibrating ions it’s more difficult for the charge carrying electrons to get through the resistor- the current can’t flow as easily and the resistance increases..
