Current Electricty Flashcards
What is the equation linking energy current and time and voltage
Energy = current x voltage x time
What is the equation linking energy charge and voltage
Energy = charge x voltage
What is the equation linking charge current and time
Charge = current x time
What is resistance
Voltage over current
What is energy measured in
Joules
What direction does current flow
Positive to negative
What happens in a parallel circuit
Cell runs down more quickly
Voltage across each branch is the same as the supply
Current in branches equal that of supply
What happens in series circuit
Voltage across the circuit = supply
Current is the same everywhere
What is a straight line graph show
Directly proportional
Why does resistance increase with voltage and current
Lamp Gets hotter so it’s harder for the current to get through this increases resistance as the particles vibrate more and it’s harder for the electrons to flow through
What is an ldr
Light dependent resistor that resistance depends on the intensity of light falling on it an example is automatic street lamps
What is mains electricity
230 volts
What is a thermistor
Temperature dependent resistor as temperature increases resistance decreased
Example of thermistor
In fridges when the fridge gets to hot the thermistor will activate the circuit
What is a diode
Allows current to flow in one way only . If diode is connected wrong way no current will flow
How do u activate diode
Voltage of 0.7 v must bbe applied to the diode
What is a rhetostat
Type of variable resistor . Long coil of resistance wire with a sliding contact .
What happens as you bring in more cool on the rhetostat
More coil increases resistance and current goes down
What is a series circuit
Single loop with only one path for charges to flow
What is a parallel circuit
Junctions so there is more than one path for current to flow
Why do bulbs glow brighter in parallel
Parallel as voltage is the same everywhere
What has a modern household circuit got
Lighting circuit
Main power circuit
What are the modern house hold circuits protected by
Lighting - 5 amp fuse
Power circuit - 30 amp fuse
Each power point in the house is protected by a fuse
What is the live wire
Comes from power station and is the most dangerous as mains voltage can easily kill you
What is the neural wire
Completes the circuit comes from power station and is earthed back to power station so does not carry as much voltage as the live wire
What is the earth wire
For safety , only carries current when there is a fault so that a fuse melts
How is the current supplied in your house
Alternating current - current flows one way and then the opposite way , 50 times each way each second
What do fuses do
Melt if current is too high and stop current flow before anything else is damaged or a fire is started
What must you do if a fuse melts
Switch off the circuit
Find reason for the fault
Replace fuse
When is the earth wire used
If a fault develops in an appliance and the live wire touches the metal case a large current flows from live wire to earth wire and the fuse breaks
Where must the fuse be placed
In the live wire so it can isolate the appliance from the live wire
What does double insulated mean
Doesn’t need an earth wire as it has an insulating plastic case so no risk of electric shock if the live wire touches casing
Why r circuit breakers better than fuses
Acts more quickly more reliable and can be reset
What is direct supply
From cell or battery of cells and has direct current meaning current only flows in one direction from positive to negative
How do circuit breakers work
A switch opens if too large a current flows and causes the circuit to be incomplete . Once the fault has been corrected the switch is reset by pressing a reset button and does not have to be replaced
What does the earth wire provide
Los resistance path for current to flow
Where should switches be in mains electricity
In the live wire so when the switch is open no electrical energy can reach the appliance if the witch was in the neutral wire electrical energy would still be able to reach the appliance and possible cause electric shock
Dangers of mains electricity
Too many plugs in one socket can cause overheating of cables and fire. Overhrating can also occur from long coiled cables
Water near sockets / switches
Frayed cables / damaged insulation
What happens to components in parralel
Can be switched on and off independently
What are the 4 equations
Charge = current x time
Energy = charge x voltage
Resistance = voltage over current
Electrical power = current x voltage
Why is the outer plug made of plastic
Good insulator so no electric shock
Why are connections in mains made of brass
Good conductor
Why are frayed wires bad
Exposes metal carrying electricity could cause electric shock
What is the purpose of the cable grip
Stops the cable and wires from being pulled out the plug
Alternating current
Current which constantly changes direction
