# electricity

what is potential difference and what is it measured in
a measure of the electrical work done by a cell (or other power supply) as charge flows round the circuit. volts (V)
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what is current
the flow of charge. the size of this is the rate at which charge flows arround the circuit
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how do you measure the amount of charge flowing arround in a circuit
in coulombs (C). one coulomb of charge is the equivalent to the charge on 6 billion billion electrons.
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what is the unit of current // how many milliamps (mA) is there in a amp
ampere (A) // 1000
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what is the difference between the flow of positve charge and the flow of electrons
.
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what is the equation for flow of charge
.
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what affects the current size
by changing the potential difference or the resistance (components within the circuit)
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what does a resistor do
limit the current flow in a circuit (high resistance = low current)
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how are voltmeters and ammeters set up, and why does the voltmeter not affect the current
an ammeter is placed in series with the resistor so the same current flows through both, s voltmeter is placed in paralel so the potential difference is the same for both. the volmeter only allows little current through
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how do you work out the potential difference across a compontent
.
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what is a kilohm and megaohm relative to a ohm
1kΩ = 1 000Ω // 1MΩ = 1 000 000 Ω
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what is an ohmic resistor/conductor? give an example of one.
a resistor in which the current through it is proportional to the potential difference. (the resistance stays the same). eg. resistor
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what is a non - ohmic resistor
a resistor in which the current flowing through it isnt proportional to the potental difference. (the resistance changes as the current flowing through it changes) eg. filament lamp, diode
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what causes the resistance to change in a filament lamp
the temperature of the filament increases as the current increases meaning the resistance increases as the temp increases. changing the p.d. makes no difference to the way the resistance changes, the resistance always increases when the temp increase
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what is a diode
component that allows current to flow in only 1 direction. in forward direction it has high resistance unil p.d has reached 0.7V. it then lets current pass. when p.d. is reversed there is extremely high resistance
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give 2 examples of variable resistors and how they react
thermistor: high resistance with low temp // LDR(light dependant resistor): low light, high resistance
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what are the rules for series circuits
1. same current through each component 2. total p.d. is shared between components but isnt the same everywhere 3. total resistance of 2 components is the sum of the resistance of each component
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what are the rules for paralel circuits
1. the total p.d. across each component is the same 2. the total current through the whole circuit is the sum of the currents through the seperate components 3. the total resistance of 2 resistors in paralel is less than the resistance of the smaller
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continued
individual resistor
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what is direct current (d.c.)
a potential difference that always rmains in the same direction and causes the current to always flow in the same direction
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what is alternating current (a.c.)
alternating potential differnce which causes the current to switch direction many times each seccond
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why will the peak a.c. potential differnce always be alittl ehigher than for example 6V
to make up for the time when the potential difference is close to 0 (it goes from 6V to -6V
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what is the mains supply
electricity supplied by alternating current. in the UK is has
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what is frequency
a frequency of 50Hz means that the cycle in alternating current repeats itself 50 times per seccond
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how thick are wires that connect the appliance to the plug and what is their maximum current
2.5mm^2 // 13 A
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what are the 3 wires in a plug called, what do they do, and what is their colour
live wire - carries the alernating p.d. from the mains supply (brown) // neutral - completes the circuit (blue) // earth - stops the appliance from becoming live (green and yellow stripes)
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what are the p.d. of the 3 wires
earth: 0V live: 230V neural: close to 0V
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what is the earth wire for
a sefety device to stop any electrical appliance with a metal casing from becoming live
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why does a resistor get hot when charge passes through it
because the electrons collide with the atoms in the resistor as they pass through it. the atoms increase their thermal energy store and vibrate faster, making the resistor hotter
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what does the amount of energy transferred by electrical work depend on
the p.d. (v) across the resistor and how much charge (coulombs (c)) flows through the resistor
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how do you calculate energy transferred (2)
.
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how do you calculate power (2)
.
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why do you want to keep the current low in overhead transmission cables
so energy isnt wasted in heating up the cables
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how do we reduce current in transmission cables
1. a generator sends a current of 100oA with 25000V into the national grid. 2. a transformer steps up the p.d. to 400 000 V but reduces the current to 62.5A so less energy is transferred into heating up cables. 3. near homes, transformers step down
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continued
the p.d. to a safer 230Vbut increase the current back uo
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what is static electricity
electricity which isnt moving (stationary)
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how does static electricity build up
when two insulators rup together, the friction causes the electrons to build up on a substance making it negatively charged and the other positively charged
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what are the electric fields on charged substances
a positively charged object the direction of the feild is away from the sphere, for the negatively charged sphere the direction of the field is towards the sphere.
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how do charged objects' fields act
the electric field is strongest closest to the charged object. the strength of the feild can be increases by adding more charge to the object
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## Other cards in this set

### Card 2

what is current

#### Back

the flow of charge. the size of this is the rate at which charge flows arround the circuit

### Card 3

#### Front

how do you measure the amount of charge flowing arround in a circuit

#### Back ### Card 4

#### Front

what is the unit of current // how many milliamps (mA) is there in a amp

#### Back ### Card 5

#### Front

what is the difference between the flow of positve charge and the flow of electrons

#### Back ## Comments

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