9 Energy Power And Resistance Flashcards
Potential difference
A measure of the transfer of energy by charge carriers
Volts
The potential difference across a component when 1 J of energy is transferred per unit charge passing through the component
W = QV
Work done = charge x potential difference
Voltmeter
Measures in parallel and ideally infinite resistance
Difference between potential difference and electromotive force
P.d. Describes the work done by the charge carriers
EMF describes the work done on the charge carriers
Special E = W / Q
EMF = work done / charge
What is an electron gun
A device used to produce a narrow beam of electrons
How does an electron gun work
Filament is heated releasing electrons through thermionic emission.
This is done in a vacuum with a large pd over the filament and the anode which has a small gap in it
E = VQ
Energy = potential difference x charge
eV = 1/2 m v^2
Work done on an electron = gain in kinetic energy
V = IR
Potential difference = current x resistance
Ohm
The resistance of a component when a p.d. is produced per ampere of current in it
Ohms law
The current in a wire is directly proportional to the p.d. across the wire
Ohmic conductor
Anything that obeys ohms law
Current p.d. graph diode
While p.d. is negative current is 0 while p.d. is small current is also 0 then increases exponentially
What effects resistance
Material
Length
Cross sectional area
R = (rho L) / A
Resistance = ( resistivity x length ) / cross sectional area
Resistance length graph find resistivity
Gradient x cross sectional area
What is the rough resistivity of conductors
10^-8
What is the rough resistivity of insulators
10^16
How does a thermistor work
As temperature increases the number of charge carriers increases and therefore resistance decreases
Describe the current p.d. graph for a thermistor
As p.d. become more negative current decreases exponentially and as p.d increases current increases exponentially
How does an LDR work
As light intensity increases more charge carriers are released increasing current and decreasing resistance
Electrical power
The rate of energy transferred by each electrical component
P = IV
Power = current x potential difference
W = VIt
Work done = potential difference x current x time
P = W/t
Power = energy transferred / time
Kilowatt-hour
The energy transferred by a device with a power of 1kW operating for a time of 1hour
1kWh
3.6 MJ
3.6 MJ
1kWh
