Chapter 27 Flashcards
(7 cards)
What is blackbody radiation?
All objects absorb and radiate electromagnetic waves (EM radiation)
For cool objects, radiation is in the infrared region of EM spectrum
The higher the temperature of the object the more atoms should oscillate
A blackbody is an ideal object that absorbs all the EM energy that falls upon it (no reflection)
As the temperature of an object increases, what are the 2 effects on the energy distribution of the radiated EM waves?
The rate of energy emission (power or intensity) increases dramatically (T^4 dependence)
The peak of the power/intensity versus wavelength curve shifts to lower wavelengths
Wien’s displacement law: λ(max)T= 2.898E-3 mK
Slide 24 March 21
What is the photoelectric effect?
When light is incident in certain metallic surfaces, electrons are emitted from the surface
Emitted electrons are called photoelectrons
No electrons are emitted if the incident light frequency is below some cutoff frequency that is characteristic of the material being illuminated
Slide 30-33 March 21
What is Einstein’s explanation of the photoelectric effect?
A tiny packet of light energy, called a photon, is emitted when a quantized oscillator jumps from one energy level to the next lower one
E=hf energy of photon
Slides 36-42 March 21
What are photocells?
Application of the photoelectric effect
When light of sufficiently high frequency falls on the cell, a current is produced
Streetlights, safety opener for garage and elevator doors, etc
What are X-rays?
Wavelengths lower than ultraviolet (frequencies higher) 0.1nm
Can penetrate most materials with ease
Roentgen discovered and worked on and didn’t try to profit from it
X-rays are produced by high energy electrons colliding with a target typically made of a metal such as tungsten, copper, etc, as electrons interacts with the target material they lose kinetic energy by emitting EM radiation (photons)
Slides 3-13 March 26
f(max)=eΔV/h λ(min)=hc/eΔV
What is Compton scattering?
Compton found that when x rays hit a target, they scattered in all directions (had longer wavelengths too depending on angle of scatter)
Photon theory explains that scattering of x rays is due to a photon-electron collision in the target material
p (momentum) = photon energy/c = hf/c=h/λ
Slides 14-20 March 26
