Topic 2-Electricity Flashcards
What is an electric current?
A flow of charge.
What is the unit of current?
Ampere.
If it is a single closed circuit what is the current like?
It is the same everywhere in the circuit.
What is the potential difference?
The driving unit which pushes the charge around.
What is the unit of potential difference?
Volts.
What is resistance?
Anything that slows the force down.
What is resistance measured in?
Ohms.
What is the relationship between resistance and current?
The greater the resistance ,the smaller the current that flows.
How do you work out charge flow?
Charge flow=current x time
How do you work out potential difference?
Potential difference=Current x resistance.
What does an ammeter measure?
The current.
What does the voltmeter measure?
Potential difference.
For diodes what does the resistance depend on?
The direction of the current.
Does the resistance of an rhombic conductor change?
No.
What does LDR stand for?
Light dependent resistor.
What is an LDR dependent on?
The light intensity.
For an LDR in a bright light what happens to the resistance?
It falls.
For an LDR in darkness what happens to the resistance?
It is at its highest.
What are LDRs used for?
Burglar detectors and automatic night lights.
What is a thermistor dependent on?
Temperature.
In hot conditions what happens to the resistance of a thermistor?
It drops.
In cool conditions what happens to the resistance of a thermistor?
It goes up.
What can thermistors be used for?
Car engine temperature detectors and electronic thermostats.
What can sensing circuits be used for?
To turn on or increase the power to the components depending off the conditions they are in.
In series circuits is the current shared equally through all components or is it the same current as the total?
The same current as the total.
In series circuits is the potential difference shared?
Yes.
If you remove a component in a parallel circuit will it most likely affect the other components?
No.
If you add a resistor to a parallel circuit what happens to the resistance?
It reduces it.
What two types of electricity supplies are there?
Alternating current and direct current.
What is the current like in an alternating current supply?
It constantly changes direction.
How are alternating currents produced?
By alternating voltages in which the positive and negative ends keep changing.
What energy source do they use in the UK?
An ac supply of 230 volts.
What does ac stand for?
Alternating current.
What’s the frequency of the ac mains supply?
50 cycles per seconds or 50 hertz.
What is direct current?
Current that’s always flowing in the same direction.
How is direct current created?
By direct voltage.
How many types of wires are there usually in electrical appliances?
3.
What are the three types of wires?
- Neutral wire.
- Live wire.
- Earth wire.
What colour is the neutral wire?
Blue.
What colour is the earth wire?
Green and yellow.
What colour is the live wire?
Brown.
What does the live wire do?
It provides alternating potential difference.
What does the neutral wire do?
It completes the circuit and carries away current.
What does the earth wire do?
It stops the appliance from becoming live.
What happens if you touch a live wire?
You will get an electric shock.
Why do you get an electric shock if you touch a live wire?
Because you body is at 0V which means if you touch a live wire a large potential difference is produced across your body from the current flowing through you.
What are the dangers of an electric shock?
Death or injury.
What does the total energy transferred by an appliance depend on?
How long the appliance is on for and it’s power.
What is the power of an appliance?
The energy it transfers per second.
What is the equation for energy transferred?
Energy transferred=power x time.
What does the power rating tell you on an appliance?
It tells you the maximum amount of energy transferred between stores per second when the appliance is in use.
How does the power rating affect the cost of the appliance?
The lower the power rating the cheaper it is to run.
Does a higher power rating mean that it transfers electricity usefully?
No.
What is the equation for energy transferred?
energy transferred=power x time.
What is the equation for energy transferred with pd?
energy transferred =charge flow x potential difference.
What is the equation for power and pd?
power=potential difference x current.
The higher the battery’s potential difference…
The more energy is supplied to the circuit for every coulomb of charge which flows around it.
What is the national grid?
A system of cables and transformers that covers the UK and connects power stations to consumers.
To transmit a large amount of power what do you need?
A high potential difference or a high current.
What is the problem with a high current in the national grid?
You lose lots of energy as the wires heat up and energy is transferred to the thermal energy store of the surroundings.
What is an advantage of a high potential difference in the national grid?
It’s much cheaper than a high current.
Why do materials get static?
When materials are rubbed together the negatively charged electrons will be scraped off one and put on to another ,leaving the materials electrically charged.
Are both +ve and -ve electrostatic charges only ever produced by the movement of electrons?
Yes.
What is a positive static charge caused by?
Electrons moving elsewhere.
As an object gains an electric charge how does this affect the potential difference?
It increases.
When is a spark formed from static?
When the potential difference is large enough to jump across the gap between the object and the earth.
Can an electric spark jump to any electric conductor nearby?
Yes.
Give an example of an electric conductor that a spark can jump to.
A human.
Opposite charges…
Attract.
Same charges…
Repel.
Where is an electric field created?
Around any charged object.
The closer you get to an object (in terms of field)…
The stronger the field strength is.
What happens when a charged object is placed in the electric field of another object?
It feels a force.(Attraction or repelling)
