4.2-Energy, Power And Resistance Flashcards
What does it mean when -ity is at the end of a word?
Means property of an object that stays the same no matter the size
Eg. Density, conductivity, resistivity
What does it mean when -ance is at the end of a word?
Means a quantity that is determined by the size
Eg. Resistance, conductance
Electrical resistance
An electric current within a metal is comprised as a flow of free electrons, collisions in the meta give rise to electrical resistance (Ω)
Factors which affect resistance
•length of object
•area of object
•material of object
•temperature of object
Electrical resistivity
A measure of how strongly a material opposes the flow of electric current (Ωm)
A semiconductor
A material which has a conductivity between that of a conductor and an insulator
Dependent on in temperature
As temperature increases the resistance decreases
Eg. LDR
Conductance
The degree to which an object conducts electricity (S)
Conductivity
The degree to which a specified material conducts electricity (S/m)
Ohms law
If something obeys ohm’s law the voltage and current are proportional
NTC (negative temperature coefficient)
As temperature increases resistance decreases
(Opposite to expectation)
Threshold p.d.
The voltage that a component conducts
Example: silicone diode is 0.7V
Potential difference
A measure of the transfer of energy by charge carriers
V= W/Q
Thermionic emission
The emission of electrons through the action of heat
Kirchoff’s second law
In any current the sum of the emf is equal to the sum of a closed loop
Σε = ΣV
around a closed loop
Potentiometer
Component which can be used as a variable resistor
