Unit 3 - Electricity Flashcards
What do we use to measure currant
Ammeter
Unit of measure for charge (Q)
Coulomb (C)
Unit of measure for energy (w)
Joules (J)
What do we use to measure resistance (Ω)
Ohms (Ω)
Unit of measure for time (s)
Seconds (s)
Unit of measure for voltage (V)
Volts (V)
Unit of measure for power (P)
Watts (W)
What are the hazards of electricity
Frayed cables (fire/electrocution), long cables (tripping), damaged plugs (fire/electrocution), water around sockets, pushing metal things into sockets (electrocution)
What is insulation
Provides a protective layer around electric wires to prevent the conduction of electricity under the influence of an electric field
What is double insulation
When the wire AND casing have a plastic cover. This stops the wire from touching the casing when the casing is an electrical conductor
What is earthing
The 3rd wire is the earthing wire. It runs current into the ground to stop current circulating on the outside (causing shocks)
What are circuit breakers
An electromagnetic switch that opens or trips when there is too much current (breaking the circuit but can be put back)
What is a fuse
Fuses contain a thin wire that melts when a certain amount of current passes through it. This permanently brakes the circuit stopping a power over,lad
Power =
P = I X V
Power (w) = current (A) X voltage (V)
Energy transferred =
E = I X V X t
Energy transferred (J) = current (A) X voltage (V) X time (s)
Voltage =
V = W / Q Voltage (V) = energy (J) / charge (C) OR V = I X R Voltage (V) = current (I) X resistance (Ω)
Current =
I = Q/ S
Current (A) = charge (C) / time (s)
Resistance =
Ω = V / I
Resistance (Ω) = voltage (V) / current (A)
Properties of mains electricity
They are A.C (alternating current). This means that the voltage / current switches directions 50 cycles per second.
It’s always 230V in the UK
Properties of direct current
Direct current (D.C) mains are powered by a battery which provides a direct current that flows in one direction at a constant rate
Rules of a series circuit
Current is equal throughout
Current depends on the applied voltage
Voltage throughout the components add up to the voltage supplied
If one appliance fails, the whole circuit fails
Rules of a parallel circuit
Voltage is equal throughout each loop
Current splits and the junctions. Total current at the junction equals the total current supplied
If one appliance fails, only that loop fails
What is current
The rate of the flow of electrons
What is voltage
The energy transferred per unit charge passed
ie.
1 volt = 1 joule per coulomb
20 V = 20 J per C
What is Ohms law
(Only works for ohmic conductors)
For conductor at a a constant temperature, the current is proportional to the voltage across it.
Straight line in a I/V graph
Give some examples of ohmic conductors
Wires
Resistors
What is a non-ohmic conductor
Does not obey ohms law. Curved I/V graph
Give some examples of non-ohmic conductors
Filament bulbs (because they heat up to much) Any type of diode Non-ohmic resistors (eg thermosister)
Effect of resistance on current
More resistance = less current can flow
Unit for current (I)
Amps - A
How to LDRs work
Light dependant resistors
More light = less resistance
How to thermistors work
More temperature = less resistance
What are lamps and LED used to show
Lamps and LEDs are used to indicate the presence of currant in a circuit.
More currant = brighter light
Charge =
Q = I X t
Charge (C) = current (A) X time (s)
What is an electric current
The flow of negatively charged electrons or of ions
Common electrical conductors
Metals
Water
Common electrical insulators
Plastic
Air
What types of charges attract/repulse
Opposite charges attract (+/-)
Similar charges repulse (+/+ or -/-)
They do this because together they become neutral
How are electrostatic charges produced
By the loss or gain of electrons
Loss = positive charge
Gain = negative charge
Describe experiments to show how insulators can become charged by friction
Cloth on balloon, balloon becomes charged, balloon sticks to wall
Explain the electrostatic phenomena in terms of the movement of electrons
Friction pulls electrons out of one object and into another
Potential dangers of electrostatic charges
When refuelling.
When a tanker moves through the air, the friction between the air and tanker causes the tanker to become charged. When you attach the metal nozzle to refuel, there could be a spark. This would ignite any fuel vapours causing a fire. To avoid this, and earthing wire is used
Uses of electrostatic charges
Photocopiers
Inkjet painting - all the pain droplets are given a similar charge (repeal each other forming a fine mist) and the car body is given an opposite charge (attracting the paint). This gives an even coating
