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  • Created by: Student_F
  • Created on: 09-01-20 22:20
What is a conductor
A material that allows electricity to flow through it easily due to the presence of delocalised electrons and/or cations
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What is an insulator
A material that does not allow electricity to flow through it easily due to the absence of delocalised electrons and/or cations
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Current
The rate of flow of charge at a point in the circuit.
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Equations of charge
"Q = It or Q = ne Q: charge (C) t: time (s) e: charge of e- (1.6x10-19) I: current (A) n: number of electrons"
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Define volt
One amp is equal to a charge of 1 coulomb passing a fixed point in the circuit every second
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Define amp
One amp is equal to a charge of 1 coulomb passing a fixed point in the circuit every second
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Define potential difference
The electrical energy converted to other forms per unit of charge moving between two points in a circuit
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Define electromotive force
The energy converted to electrical energy per unit of charge passing between two points in the circuit
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Equation for potential difference
V = W ÷ Q V: PD (V) W: work (J)
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Compare and contrast PD and EMF
"Both are measured in volts and measure work done per unit charge. PD - Refers to conversion of electrical energy to other forms and is electrical energy lost by charge EMF - Refers to a source supplying electrical energy and is electrical energy gai
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When does: 1) PD = EMF 2) PD < EMF 3) PD > EMF
"1) when no current is flowing 2) when current flows normally 3) when battery is charging"
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Why do all bulbs in a circuit light at the same time?
As delocalised electrons are present at each bulb before power supply added so there is no difference in time taken for current to reach each bulb
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Conventional current definition
hypothetical positive charge carried from the positive towards the negative terminal
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Electron flow direction
from the negative terminal towards the positive terminal
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Define resistance
The ratio of the potential difference between two points to the current passing through those points
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What causes resistance?
Resistance is caused by the collision of delocalised electrons with cations in which Ke is transferred to the cations causing them to vibrate more rapidly with increased amplitude
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State 4 factors that affect resistance and how
"Material - higher density = closer cations = less space for e- = less R Length (R∝L) - double length = double n.cations = double R Temp - increased temp = more vibrations = increased R CSA (R∝1/CSA) - more e- flow simultaneously = more collisions =
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Ohms Law
For a conductor the current through it is directly proportional to the potential difference across it, provided the temperature remains constant
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Equation for Resistance
R = V ÷ I
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Resistors in series
RT = R1 + R2 + R3
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Resistors in parallel
1/RT = 1/R1 + 1/R2 + 1/R3
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Identical resistors in parallel
RT = R1 ÷ N. R
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Define resistivity
Numerically equal to the resistance between opposite faces of a 1m cube of the material
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Differences between resistance and resistivity
Resistance measured in Ω and is a property of the conductor and varies depending on its physical dimensions whereas resistivity is in Ωm and is a property of the material that does not depend on its physical dimensions, but its atomic structure
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Equation for resistivity
 ρ =(RA)÷l
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Equation for area
A = (πd)2 ÷ 4
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What happens to the resistance of a filament lamp as current increases
The resistance increases
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What happens to the resistance of a NTC thermistor as current increases
The resistance decreases
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Principle of conservation of charge
The total current flowing into a junction equals the total current leaving the junction (∑/in = ∑/out)
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Define internal resistance
The small amount of resistance which opposes the flow of current through the object present in a power supply or battery
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Equations for internal resistance
"E = IR + Ir E = V + Ir E = I(R + r) r: internal resistance "
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Define a superconductor
A material when its resistivity falls to zero below its critical/transition temperature
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Define transition temperature
The temperature below which the material’s resistivity falls to zero
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Applications of superconductivity
"used in making electromagnets which are used in maglev trains Used in MRI scanners"
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Power Equations
P = IV P = I2R P = V2÷R W = ItV
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Electrical energy equation
E = W ÷ Q E: EMF (V)
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Define potential divider
An arrangement of resistors whereby a fraction of PD supplied to it can be passed on to an external circuit
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Potential divider equation
Vout = R1 ÷ (R1 + R2) xVin
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Other cards in this set

Card 2

Front

What is an insulator

Back

A material that does not allow electricity to flow through it easily due to the absence of delocalised electrons and/or cations

Card 3

Front

Current

Back

Preview of the front of card 3

Card 4

Front

Equations of charge

Back

Preview of the front of card 4

Card 5

Front

Define volt

Back

Preview of the front of card 5
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