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61 Cards in this Set
- Front
- Back
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Definition of an electric current
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Rate of flow of charge
The number of electrons which pass a point every second |
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Unit of electric current
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Amperes
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Symbol of electric current
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I
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How is charge carried in a metal?
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Electrons
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How is charge carried in salt solution?
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Ions
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Why don't insulating materials carry an electric current?
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Charge carriers (electrons) are held fixed in place to an atom.
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How does a battery establish an electric current?
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Forces the charge carriers to move in one direction only.
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At what temperature do electrons vibrate and become detached? What is the advantage of this?
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Absolute zero
Free to move and thus carry an electric current - act as charge carriers |
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In what direction do electrons pass round any circuit? (opposite to truth)
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Positive to negative
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Definition of charge
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Amount of charge passing a point when the current is exactly 1A
How strongly a circuit experiences an electromagnetic force. |
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Unit of charge
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Coulombs
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Symbol of charge
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Q
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Definition of potential difference/voltage
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Electrical energy converted into other forms of energy when 1 coulomb of charge passes through one point to another.
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Unit of potential difference
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Voltage
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Symbol of potential difference
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V
JC^-1 |
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What do voltmeters do?
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Measure potential difference between two points in a circuit
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What happens to the charge carriers if there is no potential difference?
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Move about at random
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Definition of power
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Rate of transfer of energy
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1 watt is equivalent to
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1 joule per second
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Unit of power
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Watts
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Definition of energy
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Work done
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Unit of energy
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Joules
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Symbol of energy
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E
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Symbol of power
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W
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Keyword for when a component converts electrical energy into other types of energy
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Power dissipation
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Definition of resistance
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Measure of the impedance of charge carriers, opposing the passage of an electric current
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What is the inverse of resistance?
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Conductivity
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Units of resistance
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Ohms
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What does a shallow gradient of a I/V graph tell you?
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High resistance within component
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What does Ohm's law state?
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Provided the temperature is constant, the current is directly proportional to the voltage across it.
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What does this graph show?
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Constant resistance - steady gradient
Current is directly proportional to voltage Follows Ohm's law |
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What does this graph show?
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Resistance changes - gradient curves (varies)
As the current rises the metallic filament in the bulb heats up and so resistance increases. Charge carriers gain kinetic energy and as a result collide more frequently Non ohmic |
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Definition of conductance
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How well a component in a circuit conducts electricity
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Units of conductance
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Siemens (S)
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Symbol for conductance
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G
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1S is equivalent to
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AV^-1
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What does this graph show?
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Resistance varies (curve)
Resistance is very high in one direction - little current for a high voltage Resistance decreases as current rises Diodes only allow current to pass in one direction - forward direction Non ohmic |
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What does this graph show?
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Resistance depends on temperature
Gradient varies (curve) general increase As temperature increases the resistance is lower Electrons inside thermistor gain more kinetic energy and as a result have enough energy to escape from their atoms and act as charge carriers - resistance lowers. Non ohmic |
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Sensitivity =
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Change in output/change in input
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Explanation of resistance
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Charge carriers colliding and as a result losing energy
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Why do batteries and cells warm u when being used?
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Internal Resistance
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What does a potentiometer/rheostat do?
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Varies resistance
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What two factors increase the resistance of a uniform metal wire?
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Length - greater distance to travel; charge carriers experience more collisions with fixed atoms. Kinetic energy is passed on and fixed atoms vibrate more
Diameter - smaller space for charge carriers to pass through and as a result experience more collisions with fixed atoms. Decreases number of charge carriers available.Kinetic energy is passed on and as a result fixed atoms vibrate more, increasing resistance. |
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Definition of electromotive force
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Amount of energy a battery produces for each coulomb of charge
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Units of electromotive force
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Voltage
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Definition of load resistance/external resistance
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Total resistance of all components in the external circuit
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Define terminal potential difference
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Potential difference across load resistance
Maximum voltage |
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If there was no internal resistance the terminal potential difference would be the same as the
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electromotive force
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Define lost volts
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Energy wasted per coulomb overcoming the internal resistance
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Electromotive force =
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lost volts (v) + terminal potential difference (V)
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lost volts =
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current x internal resistance
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Why are High Tension supplies safer?
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Have very high internal resistance and so if device is short circuited only a small current can pass through
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What is a short circuit?
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When current travels along an unintended path where there is no electrical impedance.
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Rearrange V = E - Ir to find the equation of a straight line
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V = Ir + E
E = intercept, constant I = gradient r = constant |
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The total current entering a junction =
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total current leaving junction
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The total emf around a series circuit =
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sum of p.d across each component
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Voltage and current in a series circuit:
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Current is the same at all points because there are no junctions
Electromotive force is split between all components |
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Current and voltage in a parallel circuit:
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Current is split at each junction
Voltage is the same across all components |
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Equations for the shared voltage in series circuits
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V = V1 + V2 + V3
IR = IR1 + IR2 + IR3 |
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Equations derived from shared current in parallel circuits
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I = I1 + I2 + I3
V/R = V/R1 + V/R2 + V/R3 |
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Potential difference formula=
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Vout = [R1/(R1 + R2)] x Vin
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