Electricity and Static Electricity Flashcards
Current definition
Rate of flow of electric charge
ampere, A
Potential difference definition
how much energy is transferred between two points in a circuit
1V equivalent to 1J/C
resistance definition
how much a component decreases the current
charge definition
unit carrying electrical energy (Coulomb, C)
Why resistance increases with temperature
Electrons collide with ions in lattice they flow through
This causes them to vibrate and heat up
Transfers electrical energy to heat energy
Why resistance decreases current
More ions vibrate in the lattice the electrons go through, making it harder for the electrons to go through
Ammeter function
Measures current
Must be placed in series with component
Voltmeter function
Measures potential difference
Must be placed in parallel with component
Diode facts
Only lets current go in one direction
Thermistor facts
keeping supply potential difference constant gradually heats it
As temperature increases, current through thermistor increases (resistance decreases)
Useful in electronic thermostats
LDR facts
light-dependent resistor
as light level near it increases, current increases as resistance decreases
Useful in automatic night lights and burglar detectors
I-V graph of resistors and wires
Current is directly proportional to potential difference
Straight line
I-V graph of filament lamp
Increasing current increases temperature of filament, so resistance increases, causing curve
S-shape
I-V graph of diode
Current is only allowed to flow in one direction
Diode has high resistance in opposite direction
Straight horizontal line then increasing curved line
Series circuit facts
All components must be connected or whole circuit fails
Components are connected end-to-end between +ve and -ve of power supply
Total potential difference is shared between components
Total resistance increases as more components increase
Current is the same everywhere
Parallel circuits facts
Each component is connected separately to +ve and -ve of power supply
Disconnecting one component hardly affects others at all
Potential difference is the same across all components
Current is shared between branches
Total current in is equal to total current out
Total resistance decreases as you add more components in parallel
Fuse function
Uses heat created by resistance in circuit to break the circuit when it gets too hot (current gets too high)
How filament bulbs, toasters and electric heaters work
Contains as coil of really high resistance
Causes lots of thermal energy to be emitted, causing a glowing effect
Power definition
How much energy is transferred per second
How a higher power applicant transfers less energy than a lower power appliance
Lower efficiency
Power rating definition
Maximum amount of energy transferred between stores per second when appliance is in use
What power transferred by an appliance is reliant on
Current
Potential difference
Types of electrical supplies
Batteries (d.c.) Mains supply (a.c.)
Alternating current
When the charges constantly change direction
Produced by alternating voltages (+ve and -ve ends keep alternating)
Frequency is 50Hz
UK mains supply is a.c. that supplies around 230V
Direct current
Movement of charged is only in one direction
Caused by direct voltage (negative or positive but never both)
Live wire facts
Brown
Carries voltage and alternating current of about 230V
Neutral wire facts
Blue
Completes the circuit
Electricity flows in through live wire and out through neutral wire
Always 0V
Earth wire facts
Green and yellow
For safety and protecting wiring
Carries current away if something goes wrong and stops appliance from becoming live
0V
How plug sockets are made for safety
Plastic, non-conducting casing
Switches connected to live wire of circuit so circuit can be broken and risk of electric shock is reduced
Why touching a live wire gives you an electric shock
Body is at 0V
If live wire is touched, large potential difference is produced across body and current flows through you
Caused large electric shock which could kill you
Current surge causes
Changes in a circuit e.g. appliance switching off
Fault in an electrical appliance
Fuses method
Fault develops causing live wire touching the metal case
Because case is earthed, this causes a current surge
This melts fuse, isolating whole appliance from live wire
Done so electric shock or a fire is impossible
Fuses should be rated but just above normal operating current
Larger current, thicker cable so cable doesn’t get too hot and melt
Circuit breakers method
Large current trips (turns off) a circuit breaker
They turn off quicker than time taken for fuse to melt
Can also be reset, more convenient than replacing a fuse
Circuit breakers are more expensive than fuses
Double insulated appliances
Appliances with a plastic casing and no metal parts showing
Don’t need an earth wire
Connected to a two-core cable (only live and neutral)
How static is built up by friction
Insulating materials are rubbed together
Negatively-charged electrons are scraped off one and dumped on the other
Cannot move as sandwiched between insulators so they build up
This gives both materials charge as both have lost or gained electrons
How electrically charged object (e.g. a balloon) can attract uncharged objects e.g. (a wall)
Attraction by induction
Balloon is rubbed onto something to build static
Its negative charges repel negative charges on surface of wall
Leaves a positive charge on surface of wall, attracting balloon
How static causes sparks
Static builds up on an object
If potential difference between that object and something else is
large enough, electrons can jump across the gap between charged object and earth, causing a spark
Only usually happens when gap is small
Static electricity used
Photocopiers
Reducing dust and smoke from industrial chimneys
Electrostatic sprayers
Electrostatic sprayers method
Spray gun is charged, charging up small drops of liquid
Each drop of liquid repels the other, resulting in very fine spray
Object may be given an opposite charge, attracting fine spray of liquid
If not, objects become charged by induction, attracting drops of liquid
Static electricity danger in refuelling cars
Fuel flowing out of filler pipe can build up static
This can cause a spark, igniting fuel and causing an explosion
Static electricity dangers on airplanes
Friction between air and plane causes plane to become charged
Static can the interfere with communication equipment
Static electricity dangers in lightning
Raindrops and ice bump together in storm cloud
This leaves top of cloud positively-charged and bottom of cloud negative, creating huge potential difference
Creates a spark (lightning), which can damage houses and start fires
Earthing definition and function
Connecting a charged object to the ground using a conductor
Provides an easy route to the ground, so no charge is built up
Electrons flow up from ground if charge is positive or vice verse if negative
Fuel tankers must be earthed to prevent sparks causing fuel to explode
Electric field definition
region created by any electrically-charged object in which a force would be exerted on any charged objects placed within it
Electric field diagram rules
Closer to object, stronger field
Field lines go from positive to negative
Lines are right angle to surface of object
Closer lines, stronger field
