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Physics End of Topic Revision - Coggle Diagram
Physics End of Topic Revision
Equations and measurements to know
R = Resistance (Ohms)
V = Voltage / Potential Difference (Volts)
I = Current (Amperes
Q = Charge (Coulbombs)
Q = I x t
V = I x R
P = I^2 x R
P = I x V
E = Q x V
E = P x t
E = Energy Transferred (Joules)
P = Power (Watts)
t = Time (Seconds)
Series and Parallel Circuits
Within series circuits, current remains the same without whilst voltage is shared across components. Resistance can be added up to give the circuit's total resistance
Series circuits are circuits without branches, current can only take one route
Within parallel circuits, current splits across branches whilst voltage remains the same throughout the circuit.
Parallel circuits are circuits in which branches are present and current can take more than one route.
Voltmeters and Ammeters
Voltmeters must be aligned parallel to the component you are measuring voltage at.
Ammeters must be connected in series to measure the current passing through a component.
Resistance
Resistance is the collision between electrons flowing (current) and metal ions, restricting electron flow.
Increasing resistance decreases current
In an ohmic conductor, current is directly proportional to potential difference, meaning that resistance remains the same when current is increased.
Lamps, Diodes, Thermistors and LDR's
In a filament lamp, as voltage increases so does current (though not as quickly). Current begins drop as more energy is put into the lamp because the component begins to get hot and this increases resistance.
As thermistors increase in temperature, their resistance decreases.
Diodes only allow current to flow in one direction, their IV characteristics depict this
LDR's decrease in resistance when light intensity increases
Direct Current/Voltage and Alternating Current/Voltage
Direct current/voltage (DC) is a current that does not change direction.
An alternating current/voltage is a current that changes in direction constantly, in the UK we have an alternating current/voltage as our mains electricity source.
Mains Electricity
In the UK, domestic electricity supply about 230V with a frequency of 50Hz
A three core cable is present within most plugs. This is three differently coloured wires that all have different purposes.
The live wire is brown in colour and carries the alternating voltage from the power supply (Right of the plug)
The neutral wire is blue in colour and simply completes the circuit (Left of the plug)
The earth wire is green and yellow and carries the current to the ground if there is a fault in the appliance. (Safety wire)(Top of the plug)
A fuse is present also within the plug and melts if too much current is flowing, this breaks the circuit.
National Grid
The national grid is a system of cables and transformers connecting power stations to homes.
Step up transformers are used in order to increase the potential difference that leaves the power station. This is done because high currents waste more energy than low currents.
Step down transformers decrease voltage travelling through the cables in order for it to be used domestically.
Static Electricity
When certain insulating materials rub against each other, one material loses electrons from its surface and the other gains those electrons, charging both the surfaces differently.
An electric field surrounds any charged object, if another object that has a similar charge enters that field it will experience repulsion whilst a oppositely charged object will experience attraction.
The close an object is to another similarly charged object, the stronger repulsion it will experience.
Required Practical 3 (Resistance of a wire)
This practical involves monitoring and observing a change in passing current and therefore resistance depending on the length of a wire that the current is passing through.
In this practical we should be able to observe that the longer a wire is, the more resistance it has, this is due to a longer wire having more metal ions and henceforth more ion-electron collisions
The circuit in this practical should be in series with both a voltmeter and ammeter present to calculate R = V / I
As the temperature of the wire increases, so does resistance. To prevent heating effects we can use a low voltage and turn off the flow of current between readings.
General Rules of Electricity and Definitions
Adding more resistors to a series circuit will increase the total resistance, more current it being restricted.
Adding more resistors to a parallel circuit decreases the resistance: current has more pathways to take.
Power is the rate of energy transfer
Current is the flow of charge
Voltage is the difference in energy between two points in a circuit
Resistance is reduction of charge flow