Electricity Flashcards by charlie fielding

Electrical circuits explained

Energy is supplied to electrons by a cell/battery or mains electricity. Which then move through the wires to transfer energy. Cells/ batteries have a store of chemical energy.

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What is current

The rate of the flow of charge

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How do electrons move in a circuit

The charge travels from the cell/battery to the lamp where all of their energy is converted into light

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What is potential difference

The measure of how much is energy is transferred to each coulomb of electrons/charge. Unit:volt(V)

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Where are voltmeters connected

Parallel to components

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Potential difference equation ET=C

Potential difference = energy transferred(J) / charge(c)

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Where are ammeter always components

In series with components

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Resistance meaning

The measure of how much a component/object resists the flow of current. Unit ohms

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Potential difference equations

Potential difference = current(A) x resistance(ohms)

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Fixed resistor explained

Straight line t1hrough origin. V and I are (directly proportional, constant gradient = constant R

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Filament lamp explained

Line curves, resistance not constant. This is due to delocalised electrons colliding with ionic lattice which causes them to vibrate more. A larger current results in an increased resistance(non-ohmic)

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Led-diode explained

Diodes only let current flow in one direction:low resistance in forward directions. High resistance in reverse directions

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Series circuit features

Total P.D is shared between all components
Current is the same for all components
Total resistance = sum of resistances

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Parallel circuit features

P.D for each branch=P.d of cell/battery
Current is split between the branches
Adding more resistors in parallel reduces total resistance

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Thermistor explained

Does the opposite to a metal/filament. If temperatures increases, resistance decreases.

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LDR explained

Similar to a thermistor but for light: if light intensity increases, resistance decreases.

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What is direct p.d

A p.d that only acts in one direction(results in D.C(direct current) e.g. from a battery

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Describe Neutral wire

Blue wire. Stays at 0v

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Live wire

Changes between positive and negative potentials which average out a 230 V this is UK mains voltage.
Brown wire

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Earth wire

Safety feature it acts as an escape route for a current that would otherwise cause a shock if the appliance is touched. Not needed for double insulated appliance

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What type of current is main electricity

Alternating current. Resulting from an alternating P.D. (Both of these reverse direction at frequency of 50HZ, at least in the UK)

National grid definition

Distributes electricity to where its needed

Power station

Produce a relatively high current. If this went straight into the grid, a huge amount of energy/power would be lost as heat due to the resistance of cables.

Step up transformer

Increases the transmission voltage to 132KV(132,000V) which decreases the current, less power lost due to heating in the cables.

What is static electricity

Transferred between insulating materials, they will remain charged - this is static electricity

What is the magnetic law

Opposite charges attract and like charges repel

Electron law explained

Electrons are negatively charged so if an object gains electrons, it becomes negatively charged if it loses them it becomes positively charged.

Writer the equation that links current, potential difference and power

Current = power/potential difference

What is potential difference

P.D is the measure of how much energy is transferred to/by each coulomb of electrons/charge

How are voltmeters connected

Always connected in parallel

What is current

The rate of flow of charge

How are ammeters connected

Always connected in series with component

What is resistance

The measure of how much a component/object resists the flow of charge unit ohms

What relationship do current and potential have

Directly proportional

Describe fixed resistor graph

Straight line through origin : potential difference and current are directly proportional. Constant gradient = constant resistance. It is ohmic. If another resistor gives a steeper gradient, it must have a lower resistance

Describe filament lamp graph

Line curves : resistance is not constant. This is due to delocalised electrons colliding either ionic lattice, which causes them to vibrate more, and temperature increase. A large current results in an increased resistance (Non ohmic)

Describe diode graph

Diodes only let current flow in one direction: low resistance in forward direction. High resistance in reverse direction

Describe series circuits

Total potential difference is shared between all components. Current is the same for all components. Total resistance = sum of resistances If resistors are identical, total V must be shared equally. If not, the bigger resistance takes a bigger share of voltage.

Describe parallel circuits

Potential difference for each branch = potential difference of cell/battery Current is split between the branches Adding more resistors in parallel reduces the total resistances

Describe a thermistor

Does the opposite to a metal/filament : if temperature increases, resistance decreases.

Describe an LDR(light dependent resistor)

Similar to a thermistor, but for light: if light intensity increases, resistances does

What’s is direct potential difference

Potential difference that only acts in one direction. This results in direct current(D.C) e.g. from a battery

Describe mains electricity in terms of current and potential differences

Alternating current resulting from an alternating potential difference

What voltage is the neutral wire

Stays at 0 volts

What voltage is the live wire

Changes positive + negative potentials, which average out at a P.D of 230V - this is the u.k mains voltage

Describe the earth wire

Safety feature : it acts as an escape froute for current that would otherwise cause a shock if the appliance is touched. Not needed for double insulated appliances.

What colour wire is the neutral earth and live

Live wire - brown Neural wire - blue Earth wire - yellow and green

What do power stations do in the national grid

Produce a relatively high current. If this went straight into the grid, a huge amount of energy/power would be lost and heat due to the resistance of the cables

What does a step up transformer do in the national grid

Increases the voltage(132Kv), which decreases the current, reducing the power lost due to heating in the cables.

What does a step down transformer do

Reduces the voltage down to a safer and usable 230V for homes and businesses