Unit 2 Flashcards
Classical wave
-a disturbance that transfers energy from point to point in a medium
-Classical waves exhibit diffraction and interference, and their energy is spread out continuously in space and time
Classical mechanics
A set of laws describing the motion of macroscopic objects, including F=ma, the force on an object equals the mass of the object multiplied by the acceleration of the object, and F2=-F1, where F2 is the force exerted on particle 2 by particle 1 and F1 is the force exerted on particle 1 by particle 2. Also called Newtonian mechanics, after Isaac Newton
Quantum Mechanics
The fundamental branch of physics that describes the properties, interactions, and motions of atomic and subatomic particles
wave-particle duality
the concept in quantum mechanics that quantum entities exhibit particle or wave properties according to the experimental circumstances
Amplitude (A)
-displacement of the waveform from its undisturbed position
-the distance from center to crest or center to trough of a standing or traveling wave
-ex. you take a picture of ocean and see successive crests/troughs at various times frozen
Wavelength (λ)
defined as the distance of one complete wave cycle (distance between two successive crests or troughs of wave)
crest
top of wave
trough
hollow between two wave crests
formula for Amplitude A(x)
A(max)sin(2πx/λ)
frequency (v)
-The number of cycles of a wave that pass a particular point per unit time
-the number of peaks/troughs observed moving past a fixed position in space per second
-ex. buoy in place such that it can float up/down but not side/side with waves
Light wave-particles
-do not need a medium for propagation
-they can travel through a medium
-do not have mass
-transfer energy and momentum
wave-particle duality of light
-light can either exhibit particle nature or wave nature
Light waves (electromagnetic radiation)
-comprise oscillating electric (E) and magnetic (H/B) fields propagating in the same direction but with amplitudes in planes that are perpendicular
-does not require a medium to propagate
speed of light in a vacuum (c)
c=2.998x10^8 m/s
a wave’s speed of propagation
λ x v
visible light wavelengths
light that falls in visible part of EM radiation spectrum has wavelengths between 400-700 nm
1 nm (nanometer)
1 nm= 1x10^-9 m
Rule of diffraction
-light diffracts when traversing through a slit with a width, d, that is on the order of the wavelength of the light
- λ/2<d<10λ
Double-slit experiment
-demonstrated that when light waves traverse multiple slits and diffraction patterns from the slits overlap, constructive and destructive interference occurs due to the Superposition principle
-creates “wiggles and squiggles” that occur within a broad, overall shape dictated by diffraction of related single-slit experiment
-depends on λ of the light
Constructive interference
Interaction of two waves in which their crests are aligned and their sum has greater amplitude than the original waves
Destructive interference
Interaction of two waves in which the crest of one is aligned with the trough of the other and difference shows cancellation of the original waves
Intensity of classical waves
about equal to A(max)^2
Intensity
energy transported per unit of time over a given area
Superposition principle
waves can interfere with each other constructively or destructively
Single slit experiment
-the λ stays the same before and after the slit
-noticeable diffraction occurs at the slit, we observe a broad, central peak
Photoelectric effect experiment
-shine light on a metal surface
-if light supplies enough energy, electrons are ejected
-these electrons generate a photocurrent (number of electrons in a given time)
-results cannot be explained through wave theory
-at constant power, the photocurrent decreases
-for different metals, the threshold frequency is different
-electrons will be ejected at the same threshold frequency no matter amount of power
-bringing in more photons causes higher number of electrons
-as frequency increases, photons bring in more energy, thus less photons enter, causing number of electrons released to decrease
Diffraction pattern
Arrangement of alternating bright and dark spots produced by constructive and destructive interference of two waves
Photon
a fundamental particle of light and electromagnetic radiation that has no mass and travels at the speed of light
Energy of a photon (Eph)
Eph=hv=(hc)/λ
planck’s constant
6.626x10^-34 m/s
Photoelectric effect
the emission of electrons from a material caused by electromagnetic radiation such as ultraviolet light. Electrons emitted in this manner are called photoelectrons
photoelectron
electrons which are produced when an energetic photon of radiation strikes a molecule
Gold-Leaf electroscope experiment
work function (ϕ)
-the “bonding energy” of a metal, the minimum amount of energy needed to remove the most loosely-held electrons from a metal
-Eph=hv0=ϕ
-if Eph is less than ϕ, no electrons are ejected at all
-when Eph is greater than ϕ, the “leftover energy” is transferred as kinetic energy (greater the Eph, greater the max KE of ejected electron)
correspondence between photon and ejected electron
1:1
Power
-the rate of energy transferred by the light (or EM radiation) used or generated
-Power= energy transferred/time or power x Eph = (nph x Eph)/t
Energy transferred (I)
-the process where energy moves from one system to another
-I=nph x Eph
nph
number of photons
Photon rate
-the number of photons hitting a target per unit time
-photon rate= nph/t
