# Physics As Level OCR Electricity Flashcards

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• Created by: Ellie
• Created on: 03-11-13 14:54
What is Potential Difference?
The electrical energy transferred per unit of charge when electrical energy is converted to another form
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What is Electromotive Force?
The energy transferred per unit of charge when another form of energy is transferred into electrical energy
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What is the equation relating p.d. or emf, energy and charge?
P.d. or Emf = Energy/Charge = W/Q
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What are two similarities between p.d. and emf?
They are both measured in volts and are both the transfer of energy per coulomb
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What is Number Density?
The number of free electrons per metre cubed
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What is a conductor?
A material with a high number density of conduction electrons and so a low resistance
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What is a semi conductor?
A material with a lower number density than a conductor but a higher number density than an insulator
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What is an insulator?
A material with a small number density of conduction electrons, and thus a high resistance
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What is an electrolyte?
A fluid that contains ions that are free to move and hence conduct electricity
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What is a cation?
A positive ion
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What is an anion?
A negative ion
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What is current?
Current is the rate of the flow of charge
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That is the equation relating current, charge and time?
I = Q/t Current=Charge/time
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What is the unit of current?
Amps
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What is the unit of charge?
Coulombs
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What is the unit of time?
seconds
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What is the equation relating velocity, cross sectional area, number density, charge and current?
I=vAne Current = velocity x cross sectional area x number density x charge
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What is a coulomb?
One coulomb is the total charge supplied by a current of one ampere in a time of one second
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What is the difference betweeen conventional current and electron flow?
Conventional current is said to flow from positive to negative whereas actual electron flow is in the opposite direction from right to left
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What is an ammeter?
A device used to measure electric current connected in series with the components
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What is drift velocity?
The average velocity of an electron as it travels through a wire due to potential difference
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What does an ammeter measure?
Electric current in amps
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What do you do to avoid the ammeter affecting the current?
Place the ammeter in the circuit in SERIES and make sure it has negligible resistance
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Describe an electrons movement through a metal
Delocalised electrons drift slowly through a lattice because they can only move a small distance before colliding with an atom
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How can you work out the mean velocity of the electrons? EQUATION?
I=vAne
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Example of a semiconductor and a property
Silicon and it has a lower number density
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How is an electric current produced in an electrolyte?
When salt is dissolved in water the binding force between the positive and negative sodium and chlorine ions is reduced so when an electric current is introduced the cations migrate to the cathode and the anions migrate to the anion = electric flow
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What happens when current arrives at a junction?
The current divides into two parts, with some electrons going in one direction and some in the other = charge is conserved
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What does a battery do and not do?
A battery does not produce electrical charge, it just acts as an electron pump
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What is Kirchoffs 1st law?
The sum of the currents entering a junction is ALWAYS equal to the sum of the currents leaving the junction
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What is Ohm's Law?
The current through a conductor is proportional to the potential difference across it, provided physical conditions such as temperature remain constant
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What is the equation for resistance?
Resistance = Potential Difference / Current
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What is the unit for resistance?
Volts per amp or Ohm
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Resistance is ________ to length
Proportional
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What is resistance is proportional to?
length, 1/Area,
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What is the equation for resistivity?
Resistivity = resistance x cross-sectional area / length
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## Other cards in this set

### Card 2

#### Front

What is Electromotive Force?

#### Back

The energy transferred per unit of charge when another form of energy is transferred into electrical energy

### Card 3

#### Front

What is the equation relating p.d. or emf, energy and charge?

#### Back ### Card 4

#### Front

What are two similarities between p.d. and emf?

#### Back ### Card 5

#### Front

What is Number Density?

#### Back 