Electricity Flashcards
Define current and state an equation that links current, charge and time, with units for each.
Current is the flow of electric charge, C=It
Charge-C
Current-A
Time-s
What is meant by potential difference and resistance in a circuit?
Potential difference is the driving force that pushes the charge around
Resistance is anything that slows the flow down
What is the equation that links potential difference, current and resistance?
V=IR
what is an ohmic conducter
Something that has a constant resistance that doesn’t change with the current
Name one linear component and one non-linear component
Linear-A fixed restistor (have I-V characteristics that’s a straight line)
Non-linearA filament lamp or a diode (have curved I-V characteristics)
Explain how the resistance of an LDR varies with light intensity
As light intensity increases resistance falls
What happens to the resistance of a thermistor as it gets hotter
As temperature increases resistance falls
Is potential difference shared between components in a series circuit
Yes the potential difference round a circuit always adds up to equal the source pd
How does the current through each component vary in a series circuit
In a series circuit the same current flows through all components
How does potential difference vary between components connected in parallel
In parallel circuits all components get the full source pd so the potential difference is the same across all components
Explain why adding resistors in parallel decreases the total resistance of a circuit but adding them in series increases the total resistance
In parallel all resistors have the same potential difference across them. By adding another loop, the current has more than one direction to go in therefore increasing the total current that can flow through the ciruit. An increase in currents means a decrease in total resistance of the circuit. In series they are simply added up.
What current is mains electricity
Alternating current
What is the potential difference and the frequency of the UK mains supply?
230V 50Hz
Name and give the colours of the three wires in a three core cable. Why are they colour coded?
Neutral wire-blue
Live wire-Brown
Earth wire-Green and yellow
The colour shows it’s purpose
Give the potential differences for the three wires in a three core mains cable
Neutral wire-0V
Live wire-230V
Earth wire-0V
Explain why touching a live wire is dangerous
Your body is at 0V therefore if you touch a live wire a large potential difference is produced across your body and a current flows through you, causing a large electric shock which could injure or kill you.
State the three equations that can be used to calculate electrical power
Energy transferred(J)=Power(W)xTime(s)
Power(W)=Potential difference(V)xCurrent(A)
Power(W)=Current^2(A)xResistance(Ohms)
What is the power rating of an appliance
It tells you the maximum amount of energy transferred between stores per second when the appliance is in use.
Explain why electricity is transferred by the national grid at a high pd but low current
It’s cheaper to boost the pd up really high. For a given power, increasing the pd decreases the current which means less energy is lost by the heating of the wires
What are the functions of step up and step down transformers
Step up transformers are used to increase potential difference. Step down transformers are used to reduce potential difference for domestic use
How does rubbing of materials cause static electricity to build up
When certain insulating materials rub together, negatively charged electrons will be scraped off one and dumped on the other. This will leave the materials electrically charged.
In which direction do the arrows on an electric field lines point?
From positive to negative
Using the concept of electric fields explain how a build up of static electricity can cause a spark
As electric charge builds up on an object the potential difference between the object and the earth (0V) increases. A high potential difference causes a strong electrical field between the charged object and the earthed object. the strong electric field ionises air particals. Air is normally an insulator, but when ionised is much more conductive so current can flow through it. This is the spark.
