Electrons, waves, and photons: Energy, power, and resistance Flashcards
What are the 2 factors that affect how much a device costs to run
The power usage of the device
How long the device is uded for
How does light intensity change with distance
L ∝ 1/d^2
What happens to the resistance in an LDR when light intensity increases
As light intensity increases, resistance decreases
Why does resistance fall in an LDR when the light intensity incident to the LDR increases
The semiconductor from which the LDR is constructed from releases more charge carriers when incident light intensity increases. increasing current and reducing resistance
What is ohms law
for a metalic conductor of constant temperature, the current is directly proportional to the p.d across its ends
What is the equation for Ohms law
V=IR
Define Resistivity
The product of the resistance of a component made of a certain material of known temperature and its cross-sectional area divided by its length
What is the process called when a metal filament loses electrons due to heating
Thermionic emission
What is the equation that links work done n electrons and its gain in kinetic energy
eV=1/2mv^2
What are the I-V characteristics of a diode
P.d is not directly proportional to the current
non ohmic component
non constant resistance
Behaviour depends on polarity (only works in one direction)
Define the ohm
The ohm is defined as the resistance of a component when a p.d of 1V is produced per amp of current
Define the volt
One volt is the potential difference across a component when 1J of energy is transferred per unit charge passing through the component
Describe the relationship between temperature and resistance
T∝R
Why does resistance increase when temperature increases
The positive ion s in the metallic lattice vibrate with a greater amplitude about their mean positions increasing the frequency of collisions between the positive ions and the electrons causing more work to be done on the electrons increasing resistance
Give the I-V characteristics of a resistor
p.d is proportional to the current
ohmic component
constant resistance
behaves the same way regardless of polarity
What are the 3 power equations
P=IV
P=I^2R
P=V^2/R
What is the equation for electrical energy transfer
W=VIt
Define the kilowatt-hour
The energy transferred by a device of power 1kW operating for 1hr
How many joules of energy are there in 1kWh
3.6MJ
Describe the relationship between Resistance and cross-sectional area
R∝1/A
What is the unit of resistivity
the ohm meter (Ωm)
Describe the relationship between Resistance, length and cross-sectional area
R
Describe the I-V characteristics of a thermistor
non-ohmic conductor
Similar to filament bulb but instead of current reducing as p.d increases, current increases when pd increases
non constant resistance
Why does current increase when a thermistor heats up
more charge carriers are released by the thermistor as it heats up increasing current
Describe the relationship between Resistance and length in a wire
R∝L
Derive P=VI
P/W/t
V=W/Q
W=VQ
P=VQ/t
P=VI
what is a perfect voltmeter
a perfect voltmeter has infinte resistance so that no current can flow through it
What is the unit for both p.d and emf
V
What is the unit off resiatnce
Ω (the ohm)
what is the equation for both p.d and emf
V=W/Q
What is the difference between p.d and emf
pd is the work done by a charge carrier on an electrical component and emf is the work done on a charge carrier by a power source
What happens to the resistance in a thermistor when temperatire increases
When T increases, current increases
What are the 4 factors that affect resistance
temperature, material, length and cross-sectional area
what direction must an Led point for it to light up
must follow the direction of conventional current
what is the thershold p.d for a silicon diode
0.7V
What are the I-V characteristics of a filament lamp
p.d is not directly proportional to the current
non ohmic conductor
non constant resistance
behaves the same way regardless of polarity
How does an electron gun function
A description involving the following points:
The heating of a metal filament
The loss of electrons form the filament due to thermionic emission
and applied p.d
The filament acting as a cathode to the electrons
the electrons accelerating to the anode
