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Physics GCSE: Electricity (so far) - Coggle Diagram
Physics GCSE: Electricity (so far)
Circuit symbols
Open Switch
Closed Switch
Battery (top one is a cell)
Diode
Fixed resistor
Light dependent resisitor (LDR)
Light emitting diode (LED)
Variable resistor
Lamp
Fuse
Voltmetre (-er)
Ammetre
Thermistor
Function of some of the components!
LEDs and lamps both emit light when a current passes through them- so they are used as indicators to see if the circuit works.
Fixed resistor- increases the resistance in a circuit.
Variable resistors allow you to control the amount of current going through the circuit
Circuits
Series
Where all the parts of the circuit are connected in a
single loop
The voltage produced by the batteries is shared between all the parts, equally
The current will be the same in
ALL
parts of the circuit
Parallel
Parallel circuits have "junctions" where the current splits
Current is equal throughout a branch line
The current should split equally between all lines, if the resistance in each is the same
However, this gets really complicated quickly- you don't have to be able to say
how
the current splits at GCSE, just know that
the sum current of the currents of the branch lines is the total current produced by the battery
If not, more will go to the branch line with less resistance
The voltage is the same throughout the circuit-
it is NOT shared
However, the battery has to "work harder" (not GCSE), so don't worry about conservation of energy
So all bulbs in a parallel circuit are equally bright
House lights are wired in parallel-this allows you to switch off a room (branch line) without affecting others, but also to shut off all of them using a master switch
https://revisionscience.com/gcse-revision/physics/electricity/circuits/series-and-parallel-circuits
Good diagram to show how it splits (and clear up confusion based on the diagram)
More voltage is roughly equivalent to more current
The more resistance there is, the less current
All components have at least some resistance
If cells point in opposite ways, they "cancel" each other out
ALWAYS CHECK for this in exams- it is a nasty way to catch you out!!!
At GCSE, you're told that current flows from the positive electrode to the negative-
just accept this! (even though its wrong...)
Definitions/Other facts
Current is measured in
amps/ampers (A)
- it is the constant flow of electrons around a circuit
Ammeters read the current
through
the component
Voltage
(potential difference)
- measure of how much energy is transferred between two points (in volts)
Voltmeters read the current
across
the component- always wired in parallel to what is being measured
Therefore, if a bulb is at a higher voltage, it is brighter
12V power supplies are a very common type
Equations!
I(Current)=Q(Charge)/t(Time)
R(Ohms)=V(Voltage)/I(Current)
E(electrical energy transferred)=V(Voltage)*Q(Charge)
Always start a physics question with a formula, never numbers!
Resistance makes it harder for current to flow through a circuit
Direct Current (D.C.)
Current flows in one way only
The positive electrode is at
a positive alue
all the time, the negative at 0V-
so the current only flows one way
Alternating current (A.C.)
One side of the circuit is always neutral (OV)
The other alternates between + and - 230 V (for UK mains, in America it is 110V) at a frequency of
50 Hertz
This changes its direction, but that side of the circuit is
always live
An A.C. power supply looks different from a D.C. one! (I can't find a good diagram)
Switches are always but into the
live wire
isolate the user from the always-live terminal (by "blocking" it)
Brown wire -
live wire
- pin nearest fuse
Green/yellow -
earth wire
- top middle
Blue -
neutral
- left-most pin
A fuse breaks a circuit if a fault causes too much current to flow- this protect the
wiring and appliance, as well as users
Fuses are made from wires with low melting points, designed to heat up and break past a certain threshold
Fuses in plugs are made to standard ratings- should use one designed to break at a current slightly higher than the device needs
(i.e. 3A-->5A fuse)
-
electrical appliances usually state what rating of fuse they are using.
Circuit breakers are resettable fuses, basically switches- they operate automatically, detecting faults and then stopping the flow of electricity.
They are used everywhere from household applaince to high voltage circuits supplying whole cities
The neutral wire in an A.C. Circuit (i.e. 3-pin plug) carries charge away from the appliance- most of the currents energy has been used, so its voltage is close to zero.
Earth wires prevent shocks from being given to the user if a live wire came loose in
(and touched the case of)
an appliance with an electric case
The current travels through the case, back through the earth wire
(connected to the casing)
and then through the fuse
This causes a strong current to flow through it (as earth wires have
low resistance
), and the fuse breaks
Devices such as vaccuum cleaners do
not
have earth wires- this is because they have plastic casing, or have been designed so live wires cannot touch the casing, and so
don't need it
.
They have double insulation
