Electricity

• current is the flow of electrical charge
• In a single, closed loop the current is the same everywhere in the circuit
• Potential difference is the driving force that pushes the charge around
• Resistance is anything that slows down the flow
• The ammeter measures flowing through the wire and always placed within a series circuit
• A voltmeter measures the potential difference and must always be placed in parallel around whatever you are investigating
• ohmic conductors have a constant resistance
• When electrical charge flows through a filament lamp it transfers heat to the thermal energy store which is designed to heat up. resistance increases with temperature so as the current increases the filament lamp heats up more and resistance increases
• For diodes, resistance depends on the direction of the current and they let current flow in one direction but have very high resistance if the current is reversed
• LDR is short for light dependent resistor
• LDR in bright light have a lower resistance and a high resistance in dark light - used for night lights and burglar detectors
• A thermistor is a temperature dependent resistor
• In a thermistor in hot conditions the resistance drops and in cold conditions the resistance goes up - temperature detectors
• LDRs and thermistors are used in sensing circuits
• Series circuits is where different components are connected all in a line ( except from voltmeters)
• Series circuit :

  • potential difference is shared - v total = v 1 + v 2 …..
  • current is the same everywhere - I 1 = 1 2 …
  • resistance adds up - r total = r 1 + r 2
• Parallel circuits - each component connected separately to the supply
• Parallel circuits :

  • Potential difference is the same across all components - v 1 = v 2 = ….
  • current is shared better branches - I total = I 1 + I 2
• Adding a resistor to a parallel circuit reduces the total resistance
• Mains supply is ac, battery supply is dc
• Ac supplies the current is always changing direction and alternating current is produced by alternating voltages in which positive and negative ends keep alternating
• UK mains supply is an ac supply around 230 V and 50 Hz
• Most cables have three wires :

  • live wire
  • Neutral wires
  • earth wire
• Neutral wire - blue :

  • completes the circuit
  • where current flows through
• Live wire - brown :

  • provides alternating potential difference from the mains supply
• Earth wire - green and yellow :

  • Protecting the wire and safety - stops application casing from coming live
• Live wire is dangerous as it can give you electric shock as your body is 0V so due to the current it caused an electric shock
• Energy is transferred between stores electrically by electrical appliances
• Electricity is distributed via the national grid
• the national grid is a giant system of cables and transformers that covets the Uk and connects power stations to consumers
• Transformers have two coils, primary and secondary joined with an iron core
• Step up transformer is needed to increase the potential difference so the current is decreased. this means there is left energy lost due to heat
• Step up transformers have more turns on the secondary coil then the primary
• Static electricity is caused by friction and this charges up and ends up in a spark or shock when the object moves
• When certain insulating materials are rubbed together, negatively charged electrons will be scraped off one and dumped on the other leaving the materials electrically charged
• electric fields are created around any electrically charged object and the closer to the object you get the stronger the field is
• When a charged object is placed in the electric field of another object it feels a force
• Sparks are cussed when there is a high enough potential difference between charged objects and the earth