ELECTRICITY Flashcards
What is current?
The flow of electrical charge (amps)
Rate of flow of electrons
What is potential difference?
The driving force that pushes the charge around from battery (volts)
What is resistance?
Anything that slows the flow down (ohms)
What does the flow of the current depend on?
The greater the resistance the smaller the current (for a given potential difference)
What is the relationship between current and potential difference?
They are directly proportional (resistance is constant)
What are the only resistors in which the resistance can change?
A diode
A filament lamp
What is charge?
The flow of eletrons
What is the current like through an ohmic conductor (e.g. resistor)?
The current is directly proportional to the potential difference
What is the current like through a filament lamp?
As the current increases, the temp increases so the resistance increases (curves)
What is the current like through a diode?
Current can only flow through a diode in one direction
What is the current in a series circuit?
Same
What is the potential difference in a series circuit?
Adds
What is the current in a parallel circuit?
Adds
What is the potential difference in a parallel circuit?
Same
What is the resistance in a series circuit?
Adds
What happens do the resistance in a parallel circuit?
The total resistance reduces
Current increases as more paths to go through which means decrease in total resistance because V = IR
What is an LDR (light dependant resistor)?
A resistor that is dependant on light intensity
When light increases resistance decreases (light off)
When light decreases resistance increases (light on)
What is a thermistor?
A temperature dependant resistor
When temp increases resistance decreases (off)
When temp decreases resistance increases (on)
Why do LDR’s and thermistors turn on when the resistance is increased?
Because more force is needed to push through the resister so voltage/potential difference increases
What happens to the current if you decrease the reistance?
The current increases
What will happen in a circuit with an LDR if light intensity is high?
Resistance decreases so current increases so the reading on an ammeter will increase
What is an alternating current (ac) electrical supply?
When the current is constantly changing direction created by alternating voltages
(e.g. uk mains supply at around 230V)
What is a direct current (dc) electrical supply?
When the current flows in the same direction all the time and is created by a direct voltage
(e.g. battery and cells)
What is a three-core cable?
Three wires with a core of copper and coloured plastic coating
What colour is the neutral wire?
Blue
What colour is the live wire?
Brown
What colour is the earth wire?
Green and yellow
What does the earth wire do?
Protects wiring and for safety
Stops the appliance casing from becoming live
0V
What does the live wire do?
This provides the alternating potential difference from the mains supply
230V
What does the neutral wire do?
Completes the circuit
0V
What does the fuse do in a plug?
The fuse breaks the circuit if a fault in an appliance causes too much current to flow
Where can energy be transferred to in a circuit (current)?
A moving charge (current) transfers energy because the charge does work against the resistance
The higher the current the more energy transferred to the thermal energy store
What does the power rating on an electrical appliance tell you?
The maximum amount of energy transferred between stores per second when the appliance is in use
What is the letter for charge flow?
Q
What happens when an electrical charge goes through a change in potential difference?
Energy is transferred
What is the national grid?
A giant system of cables and transformers that connects power stations to consumers (houses etc.)
How does the national grid cope with demand?
Usually runs below maximum power output so there is spare capacity to cope with high demand (usually they can predict when this will occur)
Why is a high potential difference used to transmit huge amounts of power instead of high current in the national grid?
Because a high current means you lose loads of energy as the wires heat up to the thermal energy store
How is the national grid efficient?
Boosting potential difference is cheap and doesn’t lose energy to thermal energy stores (like a high current would)
Also decreases current which decreases energy lost to thermal energy stores
What do step-up and step-down transformers do?
Step-up: increases potential difference and decreases current
Step-down: reduces potential difference so it is as a useable level for everyday electrical appliances (e.g. in a household)
What does a transformer contain?
Two coils (a primary and secondary one) joined with an iron core
What is static electricity?
Electricity in charges that are not free to move (e.g. insulation materials)
What happens when certain insulating materials are rubbed together?
Negatively charged electrons will be scarped off and dumped on the other
This will leave the materials electrically charged (one positive and one negative)
Why does too much static cause sparks?
As electric charge builds, the potential difference between an object and the earth increases (0V)
If the pd gets larger enough then electrons can jump across the gap between the object and the earth (spark)
What is electrostatic attraction / repulsion?
Opposite electric charges attract
Same electric charges repel
These forces get weaker the further apart the objects are
These forces can cause the objects to move
What is an electric field?
It is created around any electrically charged object
Where do the arrows point on an electric field diagram?
Positive = away from centre
Negative = towards centre
What happens when two oppositely charged particles move in range of each other?
Their electric fields interact
Forces act on both particles
These forces move the particles closer together
