P4,5 Electricity Flashcards
What is current?
The flow of electral charge
What can electric charge only flow around?
A closed system (completed system)
What is another way of saying voltage?
Potential difference
What pushes the electrons around a circut?
Voltage/potential difference
What is resistance measured in?
Ohms (alphs symbol)
The greater the resistance the …
Smaller the currnet
What does the current flowing through a component depend on”
The voltage and the resistance
What dies the total charge theoigh a circut depend on?
Current and time
What is current?
The rate of flow of charge
Q=IT what does Q mean?
The current flowing past a point in for a certian length of time
What is charge measured in?
Couloms
C
What is currne measured in?
A
Amps
What is an ohmic conductor?
An conductor that has a constat resiatance
Give an example of a component that is non ohmic?
Doide or lamp
What does LRD stand for?
Light Dependent Resistor
What is a LDR?
A resistor that depends on light intensity
How does an LDR react to light?
Bright light the resitance falls (easier for charge to put throuhg)
Darkness the resitance is higher
What may an LDR be used for?
Night loghts
Burgerler detenction
What does a thermestor depend on?
Temprature
How does a thermistor react to heat?
Hot conditions the resistance drops (easier to charge to flow)
Cool condition the resistance increases
What may a thermistor be used for?
Car wngine temprature sensors
Electronic thermostats
What can sensing circutes be used for?
Turning on or increasing the power to components depending on conditions that they are in
How may a thermistor control a fan?
As it gets hotter the resistance is decreased by the thermistor: this causes the fan to go faster as more voltage
What tyoe of electricity comes from the mains?
(Pur plugs/walls)
ac
What type of electricity comes from bateries?
dc
What does ac stand for?
Alternating currents
What does dc stand for?
Direct current
Describe ac supply?
The current is constantly changing direction (between positive and negative)
What is the mains supply in the UK?
230V
What is the frequency of the mains ac supply in the UK?
50 cycles per second - (cycle = changing between positive and negative)
50Hz
Describe dc?
From a battery
Same direction and is created by a direct voltage
What are the 3 types of wires in a cable?
Live wire (brown) Neutral wire (blue) Earth wire (green and yellow)
What does the live wire do?
Provides an alternating curent (230V)
Is brown
What does the neutral wire do?
It completes the circut
Around 0V
Blue
What does the earth wire do?
Protects the wires and is for saftey
It stops the appliance from becoming live
Only carries a current when there is a vault
Green and yellow
What V is your body at?
0V
Why does an electric shock happen?
When you touch a live wire a large current goes into you as your body is at 0V
Why are electric shocks so dangerous?
Even if the applience/ wire is off it could still carry a pd
There is a low resistance path between you and the wire
Why is moving a charge a type of energy?
The electorns are doing work against the resistance
What is the power rating?
The maximum safe power which the thing can operate at
What may a power rating do?
Help the customer choose which appliance to buy
What is voltage?
Energy transfered per charge passed
What is charge flow measured in?
Coublums
C
What is potential difference measured in?
Volts
How is energy distributed?
The national grid
What is the national grid?
System of cables ect which connects power stations to houses ect for energy
Hwo do power stations predict demand for energy?
Time of day
Kids coming home from school
Big wvents such as world cup finals
Why do power stations normally run below maximim power output?
So there is space to prosuce more is there is a surge in demand
Pd means what?
Potential difference
Voltage
Hoe does the national grid transfer energy?
Using set up and step down transformers
What dies a strp up transformer do?
It decreased the current and increases the voltage
Why is higher voltages used to transfer energy?
So less energy is lost through thermal energy being transfered to its surroundings
At what voltage is energy transfered at?
400,000V
What is a pylon?
One of those towers that hold up the power lines
How efficent are transformers?
Almost 100%
