Electricity Flashcards
What is an ion?
A charged atom
How does charging by friction work?
When you rub an insulator, electrons are transferred from one of the materials to the other causing them to become charged.
What type of force do two charged objects exert on each other?
non-contact force
Why do two charged objects exert a non-contact force?
A charged object has an electric field around itself.
What does each line of force represent?
the path that a small positive charge would follow because of the electric field.
If the sphere was negatively charged, what way would the lines of force point?
towards the centre of the sphere.
How does sparking occur?
When two oppositely charged objects are in close proximity and the electric field around them becomes too strong. This causes some of the electrons to be pulled out of air molecules which then hit other air molecules creating a sudden flow of electrons.
Complete the sentences: Like charges _______. Unlike charges______.
repel, attract
What is electric current?
The flow of charge/ electrons.
What is used to measure current?
ammeter
What is a battery?
two or more cells
What is electric charge measured in?
coulombs
What is the equation linking charge, time and current?
charge = current x time
What is potential difference?
The energy transferred by each coulomb of charge that passes a point.
What is the equation linking energy transferred, charge and potential difference?
potential difference = energy transferred / time
What is resistance?
when atoms resist the passage of electrons through a circuit
What is the equation linking potential difference, resistance and current?
V = IR
What is Ohm’s law?
The current through a resistor at constant temperature is directly proportional to the potential difference across the resistor.
What is an ohmic conductor?
Something that has a constant resistance whilst current changes.
Complete the sentence : The greater the resistance, the _______ steep the line.
less
What does reversing the potential diff across a resistor do to the current?
reverses it
How can you investigate how the length of a wire affects the resistance? RP
- Set up a series circuit with a cell, switch, ammeter, wire and voltmeter added in parallel.
- To add the wire tape it to a metre ruler and add crocodile clips 10cm apart.
- Calculate the resistance of the circuit using R = V/I
- Repeat by increasing the distance of the crocodile clips by 10cm each time.
- Record the results
What is a zero error?
A reading on a measuring instrument when the value should be zero.
If the temperature of the wire increases, what will happen to the resistance?
It will increase
What can you do to reduce the effects of heating when investigating the length of wire on resistance?
- Low potential difference
- Turn off the current when taking a reading
Draw a current-potential difference graph for a filament lamp.
Curved
Draw the current-potential difference graph for a diode.
Straight line across x axis then increase in current.
What direction does current flow through a diode?
One direction, called the forward direction
What way does the line curve in the forward direction of a diode?
towards the y axis
What is a diode?
a non-ohmic conductor
In the reverse direction of a diode, what is the current?
zero
What is an LED?
Light-emitting diode
What is a thermistor?
A temperature dependent resistor
What is an LDR?
light dependent resistor
What happens to the resistance of a thermistor if temperature increases?
decreases
What happens to the resistance of an LDR if light intensity increases?
decreases
In a diode, what is the resistance for the forward and reverse direction?
Forward resistance - Low
Reverse resistance - High
What is the current like in a series circuit?
The same throughout
What is the potential difference like in a series circuit?
shared between components
What is the resistance like in a series circuit?
The total resistance is the sum of the resistance of each component
What is the current like in a parallel circuit?
The total current is the sum of the currents though each of the branches
What is the potential difference like in a parallel circuit?
The same across each component
What is the resistance like of a parallel circuit?
The total resistance is less than the least resistant resistor
What does every mains circuit have?
A live wire and a neutral wire
What is current called that only flows in one direction?
direct current
What is current called that repeatedly reverses its direction?
alternating current
What is the mains frequency in the UK?
50Hz
What type of current does the mains electricity have?
alternating
Where is the neutral wire in a mains circuit earthed?
the local electricity substation
What supplies electricity to mains appliances?
the National Grid
What is the National Grid?
A network of cables and transformers
What are step-up transformers?
They increase the alternating potential difference to around 132,000 V so that a lower current is required
Where are step up transformers used?
Power stations to transfer electricity to the national grid
What are step-down transformers?
It reduces the voltage of the electricity to supply to consumers from the national grid
What voltage are homes and offices in the UK supplied with?
230V
What do plugs, sockets and cables contain?
live wires
What is the earth wire?
A wire that has 0V and carries a current only if there is a fault.
What is the use of the longest pin of a three pin plug?
It makes contact with the earth wire of a wall socket circuit so that when it is plugged in, the case is automatically earthed.
What are the pins of a plug made from?
Brass because it is a good conductor and doesn’t rust. It is harder than copper
What is the case material of a plug?
An electrical insulator, such as plastic
What is a fuse?
A component between the live pin and live wire that melts and cuts the live wire off if the current is too high.
What coloured wire is the live wire?
Brown
What coloured wire is the neutral wire?
Blue
What coloured wire is connected to the earth pin?
green and yellow striped
What material is used for the wires?
copper because it is a good electrical conductor and bends easily
What are two-core cables used for?
Appliances that have plastic cases
What volts are peoples bodies at?
0V
What is a short circuit?
when the live wire touches the neutral wire creating a large current
What are mains wires surrounded by?
An outer layer of flexible plastic material
What is the equation linking power, potential difference and current?
Power = current x potential difference
What are domestic appliances often fitted with?
a 3A, 5A or 13A fuse
What is the equation linking current, resistance and power?
Power = current^2 x resistance
How can you calculate the correct rating for a fuse?
electrical power/ potential difference
What is the equation linking charge, energy and potential difference?
energy = charge flow x pd
What does a domestic electricity meter measure?
How much energy is supplied
