Electricity Flashcards
Which side of the cell/battery is positive and which side is negative?
The longer side is positive and the shorter side is negative
What is Ohm’s law?
V = IR
What is the unit of charge?
Coulombs (C)
What is the circuit symbolf for a fixed resistor?
a rectangle
What is a property of voltage in a series circuit?
The voltage of the power source is shared across all the components
What is current measured in?
Amperes
How do you work out the resistance if given the current and voltage?
Resistance = Voltage / Current
What does the IV graph look like for a resistor?
A straight diagonal line
What is the circuit symbol for a diode?
a circle with a triangle and a vertical line
What is the circuit symbol for a fuse?
a rectangle with a line through it
What is the unit for Resistance?
Ohms
What is the connection between current and voltage in a circuit with a constant resistance?
The voltage is proportionately bigger than the current
Why does the IV graph for a diode look like it does?
Diodes only allow the current to flow in one direction, so almost no current can flow in the other direction due to the high resistance
What is the circuit symbol for an LED?
a circle with a triangle and a vertical line with 2 arrows pointing off to the top right
What 2 components take meausrement in the circuit?
Ammeters and Voltmeters
What are the 4 types of resistors?
Fixed, Variable, LDR, Thermistor
What is the circuit symbol for a LDR?
a rectangle with a circle around it with arrows pointing towards it from the top left
What 2 products can LDRs be used in?
Automatic night lamps, and Burgular alarms
What is a property of current in a series circuit?
It is the same everywhere in a circuit
How do you work out the total resistance of a series circuit?
Add up the resistance of each component
What is a property of voltage in parallel circuits?
It is the same in each loop
Which way does current actually flow?
Negative terminal to Positive terminal
What does the IV graph look like for a filament lamp?
curve towards the origin then curve away from the origin
What does the IV graph look like for a Diode?
curve upwards from the x axis just after the origin
What is the circuit symbol for a thermistor?
a rectangle with a small horizontal line which becomes diagonal and crosses the rectangle
How is the resistance affected by light in an LDR?
If the light intensity is high, the resistance is low, but if the light intensity is low, the resistance is high.
How does the resistance change which the temperature in a thermistor?
The higher the temperature, the lower the resistance and the lower the temperature, the higher the resistance
How do you show the repulsion of 2 positive particles as a diagram?
lines curves away from the 2 positive particles
What is ionisation of air?
When the air particles lose electrons and become postively charged
Why does the IV graph look like it does for a filament lamp?
As the filament heats up in the bulb, the resistance increases, which means that the graph flattens as there is a higher resistance
How are sparks able to travel between objects?
The ionised air can conduct electricity, so sparks can be seen to travel between objects
What is resistance?
Everything that resists or opposes the flow of electrons
Which way does conventional current flow?
Positive terminal to negative terminal
How do you work out the voltage if given the current and resistance?
Voltage = Current * Resistance
What is the circuit symbolf for a variable resistor?
rectangle with a diagonal arrow pointing top right across it
What is the main difference between series and parallel circuits?
There is only 1 loop in a series circuit, but there are multiple loops in a parallel circuit.
What is a disadvantage of a series cicuit?
If one component stops working or one part of the cicruit breaks, the whole cicuit will stop working
Why is a parallel circuit better than a series circuit?
If a component breaks, other components in other loops will still work
If there are more components in parallel, will the total resistance be higher or lower?
Lower
What is direct current?
Its current that flows in only one direction, so either positive or negative
What device can we use to see whether the current is AC or DC?
Oscilloscope
In the UK, the mains supply has a frequency of _____ Hz, and a voltage of _____ V.
50, 230
What is a 3 core cable?
A cable with 3 wires inside of it
What is a surge?
a sudden increase in current
What do fuses and circuit breakers do to control a surge?
They both break the circuit when the current gets too high
How do circuit breakers work?
Whenever the current gets too high, they trip and turn off the current.
What is a pro and a con of circuit breakers?
pro: They don’t have to be replaced, they can be reset
con: they are more expensive than fuses
What is earthing?
When an earth wire is provided to take away the electricity from the casing to prevent electric shocks
Why is it uncommon for charge to build up on conducting materials through friction?
Because the electrons are free to move, when they are rubbed off onto the other material, they flow back to the original one
What is the voltage of any earthed object?
0V
How does an electric field around a positive particle look like?
arrows pointing away from the positive particle in a circle
How do you show the repulsion of 2 negative particles as a diagram?
curved arrows pointing towards the negative particles
How does air become ionised?
When an object with a very stong electric field is present, the field causes the air particles to lose electrons and become positively charged.
what is a circle with an X in it?
filament lamp
What is the potential difference?
The force driving the flow of electrons
What is the unit for potential difference?
Volts (V)
Give 2 places where thermistors can be used.
Temperature receptors in car engines and electronic thermostats
What is a property of current in parallel circuits?
Current is shared between all the loops
What are the 2 ways to work out power?
Power = Current * Voltage
Power = Current2 * Resistance
What are the 2 types of current?
Alternating, Direct
Where can you find AC?
Mains supply in the UK
What 3 wires are found inside of a 3 core cable?
Neutral, Live, Earth
What colour is each of these wires: neutral, live, earth?
neutral = blue
Live = Brown
Earth = Yellow and green striped
What is the role of the live wire?
To carry the current from the mains supply to the appliance
What is the role of the neutral wire?
To complete the circuit by carrying the current back to the mains supply from the appliance
What is the voltage of the neutral and earth wires?
0 V
What can cause a surge?
When you turn an appliance on or off
A fault in the circuit, or appliance
What are 4 safety precautions for surges?
Fuses, Earth wires, Double Insulation, Circuit Breakers
What is a pro and a con of Fuses?
pro: They are simple and cheap
con: They have to be replaced everytime they are blown
What is double insulation?
When the appliance is coated in an insulator like plastic and has no exposed metal parts. This means that you can’t get an electric shock by touching it.
What is static electricity?
The build up of charge on insulating materials
What happens when 2 materials are rubbed against each other?
The electrons in one material are rubbed of onto the other material leaving one of them negatively charged and the other positively
Can a charge build up on a conductor?
yes, but it is much less common
Which ways do arrows point in an electrical field?
Positive to negative
Where is the electrical field the strongest?
Close to the particle, and it gets weaker the further away you get
What is the force between 2 oppositely charged particles?
Electrostatic force
How do you show the attraction between 2 particles as a diagram?
curved lines from the positive particle to the negative particle
How are sparks able to travel between objects?
The ionised air can conduct electricity, so sparks can be seen to travel between objects
How does a fuse work?
Fuses have a very thin wire inside them. When the current gets too high, the wire melts, which breaks the circuit
How does an alternating current work?
The direction of the current constantly changes back and forth.
If something is double insulated, will it need an earth wire and why?
No because an electric shock cannot be given by the casing as it is coated in an insulator
What are the wires made of in 3 core cable?
Copper
What formula links Energy, Voltage, Current and Time?
E = ItV
What formula links Energy, Power and Time?
E = P*t
What formula links Power, Current and Resistance?
P = I^2 * R
What happens if the size of the negative static charge on an object builds up?
a potential difference is created between the object and any earthed object
What happens when 2 materials are rubbed against each other?
The electrons in one material are rubbed of onto the other material leaving one of them negatively charged and the other positively
What happens when the potential difference is big enough between a static charged obhject and an earthed object?
The electrons can jump across the gap, which causes a spark
What is charge?
how much current flows in a certain amount of time
What is the role of the earth wire?
If the live wire came lose and touched the casing, the casing would become live and if we were to touch it, we would get an electric shock. The earth wire provides an alternative pathway for the current to return, so we do not get shocked if the live wire becomes lose and touches the casing
What risks come from surges?
Damage to the appliance
Fires
Electric Shocks
Where can you find DC?
In cells or batteries
Which of the 2 materials gets a positive charge and which one gets a negative charge?
The one that loses the electrons has a positive static charge and the one that gains the electrons has a negative static charge. It depends on the materials, which way the electrons move
Why is it uncommon for charge to build up on conducting materials through friction?
Because the electrons are free to move, when they are rubbed off onto the other material, they flow back to the original one
Will loops with higher resistances have a lower or higher share of the current?
Lower share
