Topic 5- Electricity And Circuits Flashcards
Current
The rate of flow of charge.
What will a component need for a current to flow through it?
Needs a potential difference and complete circuit
Potential difference
Energy transferred per coulomb of charge that passes between 2 points in an electrical circuit.
Current units
Amperes (A)
Potential difference units
Volts (V)
Resistance
Anything that slows the current(flow) down
Unit of resistance
Ohm
2 things current depends on
Potential difference
Resistance
Charge formula
Current*time
Volt
One joule per coulomb
What causes current in metals?
Flow of electrons
Q=
IT
E=
QV
Energy transferred
Charge moved * potential difference
1 volt
1 joule per coulomb
V=
IR
Potential difference
Current * resistance
What can you use to change the current?
A variable resistor
What does charge have to work against?
What does this cause? What’s the side effect of this? Why?
Charge has to work against resistance, causing electrical transfer. This can be a useful transfer pr can be dissipated to thermal energy stores/surroundings. This is because the electrons collide w ions in the lattice , giving them energy to vibrate and heat up.
What happens as the resistor heats up in a given pd?
The current decreases
*with exception of thermistor which increases current as it heats up
What is an ammeter? Where does it go in a circuit?
A component used to measure current (amps), is placed in SERIES w the component.
What’s a voltmeter? Where do you place it in a circuit?
A component used to measure potential difference, is placed in PARALLEL to a component.
What’s an IV graph?
A graph used to show current against potential difference.
What does the IV graph of a resistor show?
That current is directly proportional to potential difference (linear graph).
How do you work out the resistance from an IV graph?
Resistance= 1/gradient
What does the IV graph of a filament lamp look like?
Curved as increasing current = increasing temp of filament
What does the IV graph of a diode look like?
Shows a non-linear graph only increasing on one side of graph as diode has high resistance in opposite direction.
What’s the relationship between lights nd resistance in an LDR (Light dependent Resistor)
As light dims, resistance increases
Dim = highest resistance
Bright= lowest resistance
How are LDR’s used?
As automatic night lights/ burglar detectors/ outdoor lighting
What’s the relationship between temp and resistance in a thermistor?
As temp increases, resistance lowers
What’s a series circuit?
A circuit with different components connected in a line from positive to negative power supply ends.
What are the negatives of a series circuit?
Can be broken easily if the circuit becomes disconnected
How does current stay in a series circuit?
Current is THE SAME everywhere
What happens as you add resistors to a series circuit?
The resistance increases and so the total current of the series circuit reduces
What’s a parallel circuit?
A circuit in which each component is separately connected to the positive and negative ends of supply.
What’s the advantage of a parallel circuit?
Removing a component wont affect the other components
How is the p d spread across all components ?
It’s the same across all components
How is current spread between components?
It’s shared between branches
Total current going into a junction =
Total current leaving
What happens when you add a resistor to a parallel circuit
Adding a resistor into a parallel circuit reduces the total resistance due to more loops meaning the currents can travel in more than One Direction.
Energy transferred =
Current *potential difference *time
E=
IVT
What happens if the temperature of the circuit is too high?
The circuit will melt and resistance will increase
How is the heating of electric current used to our advantage and toasters?
Toasters have a wire coil coil with a very high resistance so when electricity is passed through, give the IR radiation to transfer heat energy to bread to cook it. Can also be used in filament lightbulbs and electric heaters
Power
Energy transferred per second
Unit of power
Watts
Power equation
Energy transferred/ time
Current * Potential difference
P=
IV
Or
IsquaredR
What are the two types of current
Alternating/direct
What is alternating-current
Current in which the movement of the charges are constantly changing direction (alternating voltages w + & - ends of pd alternate)
What is direct current
Current in which the movement of charge is only in One Direction, is created by direct voltage
What is the UK mains supply current
It is an alternating-current at roughly 230 V with a frequency of 50 Hz
What currency do cells and batteries supply
Direct current
Livewire
The wire that carries voltage/potential difference. It alternates between positive and negative at about 230 V
Neutral wire
The wider complete the circuit, flows into live and flows out through neutral. Holds 0v
Earth wire
The way of protecting the wiring by carrying current away if something goes wrong and stops the casing from becoming live. Hold 0 V
Why do you get electric shock?
Because your body, like the earth, is at 0v si live wire can pass large p.d through body to get to earth.
Surge
A sudden increase in current
What are surges caused by
Changes in a circuit/fault in an appliance
What can surges cause
The melting of an appliance
Fire
fatal electric shock
What prevent the affects of surges
Earth wires or fuses
How do Earth wires work
If livewire touches the Earthed metal case, The current flows through the case and out through the Earth wire.
How do fuses work
A search in current will melt if you amount of current is above fuse rating, this is connected to the live wire so breaks fuse, isolating appliance, Preventing electric shock or fire.
What type of wires do you need if you are carrying a large current
Thicker wires
What are circuit breakers
Something that can be used instead of household fuses which will be tripped when a large current flows through it, isolating the appliance before the fuse would melt. Can be reset (don’t need to be replaced)
Double inselation
When an appliance has plastic casing and no metal showing
Two core cables
Cable only carrying earth and live wire as appliance may be double insulated.
Live wire in electrical contact with the neutral wire
Closed loop is formed where current from live is carried away by neutral so no current will flow away from appliance.
Purposes of insulation covering live wire
To stop electrical current flowing out of live wire and causing an electric shock.
To allow identification of the wire.
Danger of receiving electric shock even if socket is switched off
Although there’s no current flowing, a potential difference still exists within the wire. So current can still flow through.
Purposes of fuses in fuse boxes
To protect wiring of a house and prevent electrical fires.
