Electricity Flashcards
Current
The flow of electric charge
The greater the resistance across a component , the smaller the current that flows
Measured in ampere A
Ammeter measures current
It must always be placed in a series circuit
Potential difference
The driving force that pushes the charge round
Unit is Volt , V
Voltmeters measure
potential difference
Voltmeters must always be placed in parallel around whatever your investigating
Resistance
Anything that slows the flow down
Unit ohm
Ohmic conductors
A conductor that has a constant resistance when kept at a constant temperature
The graph is a straight line through origin (the steeper gradient of the graph the smaller the resistance of resistor)
Potential difference is always proportional to the current
Series circuit
Components are connected in a line. If one component is broken they all stop.
Potential difference is shared between components. So the pd round a series circuit adds to equal the source pd
Current is the same everywhere. The size of the current is I = V/R
I1=I2 etc
Resistance adds up because adding a resister means they have to share the potential difference so R total = R1 + R2 etc
Parallel circuits
Components are connected separately to the +ve and -ve of the supply.
Potential difference is the same across all components so all components get the full force pd
V1=V2
Current is shared between branches as the total current going into a junction is the same as the total exiting the junction I total = I1 + I2 etc
Adding a resister reduces the total resistance
Ac and Dc
Mains supply is ac, battery supply is dc
In ac supplies the current is constantly changing direction as alternating currents are produced by alternating voltages where the positive and negative ends keep alternating
UK mains supply in ac is 230V
The frequency is 50Hz
Direct current is a current that is flowing in the same direction created by direction voltage
National grid
A giant system of cables and transformers that connects from power stations to consumers
Uses a high pd and low current. This is because high currents transfer loads of energy to thermal. It’s much cheaper to boost pd really high
Pd is changed by a transformer. Step up increases the secondary coil has more turns than primary coil. Step down reduces as primary coil has more turns than secondary coil.
How is Static electricity caused
Caused by friction. When insulating materials are rubbed together , negatively charged electrons will be scraped off one and dumped on the other.
Sparks
As electric charge builds on an object so does the potential difference. If this gets large enough , electrons can jump across the gap between the charged object and the earth. They can also jump to any earthed conductor that is nearby.
Electric fields
Created around any electrically charged object
The closer you get to the object the stronger it is
Electric field lines go from positive to negative. Always at right angle. The closer together the lines the stronger the field is.
Live wire
Brown
The route ac current takes when entering an appliance (anything that transfers energy from one form to another)
Neutral wire
Blue
Completes the circuit
The route ac current takes when exiting the appliance
Voltage is close to 0
Earth wire
Yellow / green
Acts as a safety pin
Earth pin is longer than live and neutral pins therefore Earth pin connects with socket first when something is plugged in providing you with the earthing safety
Earth wire connects to Earth pin taking current away from the appliance , into the wiring of the house and down through the Earth via the houses earthing system
LDRS
Light dependent resistors
As light intensity increases , resistance decreases
As resistance decreases potential difference also decreases
Thermistors
Temperature dependent resistors
As temperature increases , resistance decreases
As resistance decreases potential difference also decreases
