module 4 part 1 electricity Flashcards
Ohms law
The current and potential difference through an ohmic conductor
held under constant physical conditions are directly proportional, with the constant
of proportionality being resistance
current
The rate of flow of charge in a circuit
charge
a physical quantity, which can be either positive or negative. It is measured in coulombs (C)
ions
an atom that has either lost or gained electrons and so has net charge
conventional current
model used to describe electrical current in a circuit - conventional current travels from pos to neg - it is the direction in which pos charge would travel
kirchoff first law and equation
at any point in an electrical circuit, sum of currents in that point is equal to sum of currents out, electrical charge conserved
∑I in=∑I out
number density
the number of free electrons per cubic metre of a material, symbol n
potential difference
energy transferred from electrical to other forms of energy (e.g. light) per unit charge. Work is done on component
EMF
the work done on charge carrier per unit charge, measured across power supply.
cathode and anode
anode - positively charged electrode
cathode - negatively charged electrode
electron flow moves from cathode to anode, conventional is opposite
thermionic emission
the emission of electrons from surface of hot metal wire
temp and res graph explained
diode symbol and direction
difference between emf and pd
Pd - energy transferred from electrical to other forms of energy (e.g. light) per unit charge. Work is done on component.
Emf - energy transferred from source of power (e.g. chemical energy) to charge carriers. Work done on charge carrier.
Conservation of Charge
The total charge in a system cannot change
Electrolytes
Substances that contain ions that when dissolved in a solution, act
as charge carriers and allow current to flow.
Elementary Charge
The smallest possible charge, equal to the charge of an
electron
Insulators
A material that has no free charge carriers and so doesn’t allow the
flow of electrical charge.
Mean Drift Velocity
The average velocity of an electron passing through an
object. It is proportional to the current, and inversely proportional to the number of
charge carriers and the cross-sectional area of the object
Quantisation of Charge
The idea that charge can only exist in discrete packets
of multiples of the elementary charge.
Semiconductors
A material that has the ability to change its number of charge
carriers, and so its ability to conduct electricity. Light dependent resistors and
thermistors are both examples.
Diode
A component that allows current through in one direction only. In the
correct direction, diodes have a threshold voltage (typically 0.6 V) above which
current can flow
Electromotive Force
The energy supplied by a source per unit charge passing
through the source, measured in volts.
Filament Lamp
A bulb consisting of a metal filament, that heats up and glows to
produce light. As the filament increases in temperature, its resistance increases
since the metal ions vibrate more and make it harder for the charge carriers to
pass through.
I-V Characteristics
Plots of current against voltage, that show how different
components behave
Kilowatt-Hour
A unit of electrical energy. It is usually used to measure domestic
power consumption.
Light-Dependent Resistor
A light sensitive semiconductor whose resistance
increases when light intensity decreases
Ohmic Conductor
A conductor for which the current flow is directly proportional
to the potential difference across it, when under constant physical conditions
Ohm’s Law
The current and potential difference through an ohmic conductor
held under constant physical conditions are directly proportional, with the constant
of proportionality being resistance.
Potential Difference
The difference in electrical potential between two points in a
circuit. It is also the work done per coulomb to move a charge from the lower
potential point to the higher potential point. It is measured in Volts
Power
The rate of energy transfer in a circuit. It can be calculated as the product
of the current and the potential difference between two points. It is measured in
Watts
Resistance
A measure of how difficult it is for current to flow through a material
resistivity
A measure of how difficult it is for charge to travel through a material.
It is proportional to the object’s resistance and cross-sectional area, and inversely
proportional to the object’s length. It is measured in Ohm metres
