Module 4 Flashcards
Define electric current
Rate of flow of charge
Why is charge quantized
It is always a multiple of e
Define electrolyte
Liquid that conducts electricty
How does a liquid conduct electricity
Ions
What charge is an anode
Positive
What charge is a cathode
Negative
Kirchoffs First law
For any point in an electrical circuit, the sum of the currents into that point is equal to the sum of the currents out of that point (conservation of charge)
Define conductor
High number density
10^28 (free electrosn per meter cubed)
Define insulator
Low number density
Define semi- conductor
Number density around 10^17
In order to carry the same current, the electrons must move faster so the material becomes hotter
What is v in I=Anev
Mean drift velocity
Define electromotive forcce (emf)
Describes work done on the charge carriers
Define potential difference
Work done by the charge carriers
Define thermionic emmision
The emmission of electrons through the action of heat
Define ohms law
For a metallic conductor kept at a constatnt temperature, the current in the wire is directly proportional to the p.d. accross its ends
What are the I - V characteristics of a resistor
Obeys ohms law (ohmic conductor)
the resistor behaves the sme regardless of polarity
What are the I - V characteristics of a filament lamp
Non-ohmic component
The resistance is not constant
Behaves the same regardless of polarity
What are the I - V characteristics of an LED
Non-ohmic component
The resistance is not constant
The diodes behaviour depends on the polarity
Resistance decreases at threshhold p.d. and light is emitted
Resistivity of conductors
10^8 ohmmmeters
Resisitivity of insulators
10^16 Ohmmeters
What is a negative temperature coefficient
Resistance drops as temperature increases (thermistor)
What are the I- V characteristics of a thermistor
Non ohmic component
The resistance is not constant
Behaves the same regardless of polarity
What is a light dependant resistor
A resistor that decreases resistance for increasing light intensity
What is a light dependant resistor
A resistor that decreases resistance for increasing light intensity
Define electrical power
Rate of energy transfer by each electrical component
Define kilowhatt hour
Unit of energy (power x time)
What are lost volts
The difference between the terminal p.d. and the actual emf.
emf = terminal pd + lost volts
What are the different components in emf=I(R+r)
R = Resistance of circuit
r = internal resistance
How can Vout be varied
Variable resisitor
Define transvese wave
Oscilaltions are perpendicular to direction of energy
They have peaks and troughs
Define longitudinal wave
Oscilations are parallel to direction of travel
They have compressions and rarefractions
Define phase difference
Difference in displacement of particles along a wave measured in radians
360degrees = 2pi radians
Define antiphase
Phase difference of 180 degrees or pi radians
State the law of reflection
The angle of incidence is equal to the angle of reflection
When waves are reflected their wavelength and frequency remain unchanged
Define refraction
When a wave changes direction as it changes speed when passing from one medium to another
whenever there is refraction there is partial reflection
Define intensity
Radiant power per unit area
I i proportional to amplitude^2
What is an em wave
Wave that can travel through a vacuum
EM spectrum
Radio, Microwave, Infrared, Visable, ultraviolet, x-rays, Gamma.
Which em waves have the longest and shortest wavelength
Longest = radio
Shortest = gamma
Wavelengths of visable light
700nm (red)
400nm (purple/ blue)
Refraction law when light travels from one medium to another
n1sin1 = n2sin2
When does total internal reflection occur
When light strikes the boundry above the critical angle
Critical angle is measured against the normal
State the principle of superposition
When two waves meet at a point, the resultant displacement at that point is equal to the sum of the displacements of the individual waves
Define coherence
2 waves having constant phase difference
When does destructive interference/minima occur
(n+0.5)wavelength
When does constructive interference/ maxima occur
(n)wavelength
What light is used in youngs double slit experiment
Monochromatic
Define node and antinode
Node is whewre two waves meet
Antinode is where 2 waves are furthest apart
Define electron volt
The energy transferred to or from an electron when it moves though a potential difference.
What is the photoelectric effect
High energy electromagnetic radiation causes electrons to be emmitted from the surface of a metal
Electrons only emitted if incident radiation was above the threshold frequency
What did the gold leaf electroscope prove
How electrical charges repel each other
Define work function
Minimum energy required to free an electron from the surface of the metal
Are standing waves longitudinal or transverse
Longitudinal
What happens in a LDR
As light increases resistance decreases
