Electromagnetic Radiation(quiz #2) Flashcards
(34 cards)
What are x- rays produced from?
x-rays are produced by the rapid deceleration of high speed electrons as they strike the anode in a CRT. When electrons strike a metal target, the kinetic energy of the electrons is converted in x-ray energy(i.e. photon energy that has a frequency in the x-ray range
Derive the formula to find the energy of the kinetic energy of the photon and electron as well as the potential energy of the voltage source for an x-ray.
E(p, voltage source) = E(k, electron) = E(photon)
q(delta)V = (1/2)mv^2 = hf
Describe Willheim Roentgen’s experiment and what he observed & concluded.
Roentgen performed CRT experiments ar higher voltages and noticed the a fluorescent screen glowed even when placed several meters outside of the CRT and also when black cardboard was place in front of the screen. He concluded that the effect was caused by a mysterious type of radiation called x-rays.
What are the wave and particle characteristics of x-rays?
Wave: X-rays penetrate opaque objects such as wood, paper, aluminum, and human flesh(does not penetrate bone). They are diffracted by atoms in crystals.
Particle: X-rays ionize gases and water by colliding with electrons and driving them off the molecules, leaving the molecules positively charged.
In Comptons equation for the change in wavelength of the x-ray photon, what is 0 equal to when trying to maximize?
0 = 180 degrees
Describe the Compton scattering Experiment? Draw the apparatus.
Compton bombard an electron with x-rays to test the idea that a photon has momentum. The incident x-ray photon would hit an electron at rest. As a result, the electron would go in one direction and the scattered x-ray photon would go in another. He then measured the wavelength of the incident and outgoing x-rays as well as the angle of the scattered photon. Because the experiment obeyed the law of conservation of momentum, Compton confirmed that a photon has momentum.
What does it mean if a collision is elastic?
NET momentum and NET kinetic energy are conserved
Derive the equations Compton discovered when using the conservation of energy and conservation of momentum.
Conservation of energy:
E(before) = E(after)
E(1B) + E(2B) = E(1A) + E(2A)
(hc)/(~(1B)) = (hc)/(~(1A)) + (1/2)(mv(2A)^2)
Conservation of momentum:
(sigma) p(B) = (sigma) p(A)
p(1B) + p(2B) = p(1A) + p(2A)
p(1B) = p(1A) + p(2A)
remember vector signs on everything
Use the equations for momentum and E=mc^2 to prove that a photon can have momentum.
p = mv(*)
E = mc^2 –> m = E/(c^2) (**)
(**) into (*)
p = (Ev)/(c^2) –> p = (Ec)/(c^2) –> E=pc
p = E/c –> (hf)/c –> p=h/~
What is light spectra?
Coloured patterns produced when light is either dispersed through an equilateral glass prism or spread apart by a diffraction grating.
How is a continuous spectra produced?
White light is produced from a dense liquid or solid under high temperature and pressure. this produces a continuous spectra of colour, with shorter wavelengths refracted more(violet)
Describe the Franck-Hertz Experiment. Explain the observations and conclusions.
- High energy electrons were fired though mercury vapor.
- Observations: the mercury vapor could only absorb energy at discrete energies of 4.86eV, 6.67 eV, & 8.84eV (&10.4eV)
- ConclusionsL Atoms absorb only discrete amounts of quanta of energy. Electrons in atoms have a number of excitation states
Electrons normally exist in ________(1). When electrons are given a quantized amount of energy, they jump into _____________(2). Only certain excitation states are allowed. Therefore, electrons cannot ___________________(3)
(1) a ground state(lowest energy state)
(2) an excited energy state
(3) exist in intermediate states
What happens when an electron drops to a lower excitation state?
Energy is released in the form of a photon. Franck and Hertz then measured the wavelength of light emitted by the excited mercury atoms.
What is ionization energy?
The amount of energy required to force an electron to leave the atom(when n= infinity)
What is the ground state?
The lowest possible energy state that an electron can exist in.
What is the emission or bring line spectra?
If a low pressure gas is sealed inside a tube with an anode and cathode, it will become hot(excited) and glow when electricity is passed through. This produces a spectrum of bright coloured lines against a black background. The colour and location of the lines is dependant on the type of excited gas used.
Coloured lines with lot’s of black
Emission spectrum has more lines than the absorption spectrum
What is the absorption or dark line spectrum?
White light passes through a cool(unexcited) gas before dispersing or diffracting. The unexcited has in the container absorbs a few discrete wavelengths or colours of light. This produces a continuous spectrum but with dark lines of missing light.
Black lines with lot’s of colour
The frequency of light absorbed by the unexcited gas from white light exactly matches the frequency of light emitted by the excited gas.
Absorption spectrum has less lines than the emission spectrum.
What is the equation Johann Jacob Balmer found in 1885 which predicted the wavelengths of the four emission lines in the hydrogen spectrum? What is R(H)?
(1/~) = R(H) ((1/2^2) - (1-n^2))
R(H) = 1.097 x 10^7 m^-1
n starts at 3
How do a wave and particle differ?
Wave: Continuous, diffraction, interference, polarization
Particle: Discrete, has mass os it also has momentum
How does an electron and photon differ?
An electron has mass and charge while a photon has no mass and no charge.
How are absorption spectra created?
Two ways electrons in the atom can absorb energy:
(a) collision with high energy particles(electrons): Electrons in the atom absorb only the amount of energy corresponding to jump from the ground state to an excitation state. Incoming electron continues on with remain gin energy
(b) Absorbing a photon: atoms will only absorb photon which have energies that exactly match the excitation energies.
How is an emission spectrum created?
once atoms are excited they will eventually fall back to the ground state in two different ways:
(a) straight from the excitation state to the ground state: In this case, one high energy photon is released
(b) Through a series of intermediate excitation states to the ground state: In this case, several lower energy photons are released.
Who was Niels Bohr? What did Bohr predict?
Used Hydrogen fro this atomic model due to its simplicity(one electron orbiting around a photon)
Predicted that the emission spectra of hydrogen gas was somehow related to the structure of the atom
