Section 2 - Electricity Flashcards
Three types of wire in a plug?
- Live wire(brown)
- Neutral wire(blue)
- Earth wire(green/yellow)
- p18
Metal parts are made of…
Copper or brass(good conductors)
The rest of the plug is made of…
rubber or plastic(good insulators and flexible)
The live wire
-Alternates between high +VE and -VE voltage of about 230V
The neutral wire
-Is always at 0V
The earth wire
- Earths the appliance
- Carries the current away if a fault develops
- An earthed conductor can never become live
Normal flow of electricity in a plug
In through the live wire and out through the neutral wire
How the earth wire and the fuse works
- A fault develops where the live wire touches the metal case
- A large current flows through the live, through the case, then out down the earth wire
- The surge melts the fuse(or trips the circuit breaker)
- This isolates the appliance, making it impossible to get an electric shock
Advantage of a surface breaker
- It opens a switch when a surge is detected
- This breaks the the circuit
- Can be easily reset
Resistors
- Heat up when there is an electric current
- Heat increases the resistance of a resistor
- Therefore less current will flow
- This can cause components to melt
Formula for electrical power
P = I*V
What is electrical power?
Electrical power is the rate at which an appliance transfers energy
What does a higher power rating mean?
More energy is transferred in a short time; thus the appliance will draw a large current from the supply
Unit for power
watts(W)
Rating of fuses
Fuses should be rated as near as possible, but slightly higher than the normal operating current
Formula for energy transferred
E = IVt
Current
The rate of flow of charge round the circuit(A)
Voltage
The energy transferred per unit charge passed
Resistance
Anything in the circuit which slows the flow down(Ω)
Effect of increasing the voltage
More current will flow
Effect of increasing the resistance
Less current will flow
Formula for voltage
V = I*R
Voltage-current graphs
Metal filament lamp - As temperature increases, the resistance increases
Wire - The current through a wire(at constant temperature) is proportional to voltage
Different Resistors - The current through a resistor is proportional to voltage
Diode - Current will only flow through a diode in one direction
p22
LEDs
- Light emitting diodes
- Emit light when current flows through them in the forward direction
- Don’t have a filament that can burn out
LDR
- Light-dependant resistor
- As light increases, the resistance decreases
- As light decreases, the resistance increases
Thermistor
- A temperature-dependant resistor
- As heat increases, the resistance decreases
- As heat decreases, the resistance increases
Layout in a series circuit
All the components are connected in a line
Characteristics of a series circuit
- Cannot control which components current flows through
- Removing or disconnecting one component will break the circuit
- Only a few things are connected in series(e.g fairy lights)
- The same current flows through all parts of the circuit
- Size of the current is determined by the total voltage of the cells, and the total resistance of the circuit
- The total resistance depends on the number of components and the type of components used
Layout in a parallel circuit
Each component is separately connected to the +VE and -VE of the supply
Characteristics of a parallel circuit
-Removing or disconnecting one of the components will hardly affect the others
How is charge carried in a solid metal conductors?
By negatively charged electrons
Formula for charge
Q = I*t
Definition of a volt
One volt is one joule per coulomb
How does static build up?
- Two insulating materials are rubbed together
- The electron are scrapped off one and dumped onto the other
- This results in opposite electrostatic charges
- Electrically charged objects attract small objects placed near them
How can negative charge be discharged safely?
By connecting the charged conductor to the earth with a metal strap: The electrons flow down the strap if the charge is negative, and flow from the ground if the charge is positive
How are sparks caused by static electricity?
The greater the charge on an isolated object, the greater the voltage between the object and the earth: When the voltage gets great enough, a spark is created which jumps across the gap
