Electromagnetic Radiation(quiz #2)

Question 1

What are x- rays produced from?

Answer 1

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

Question 2

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.

Answer 2

E(p, voltage source) = E(k, electron) = E(photon)

q(delta)V = (1/2)mv^2 = hf

Question 3

Describe Willheim Roentgen’s experiment and what he observed & concluded.

Answer 3

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.

Question 4

What are the wave and particle characteristics of x-rays?

Answer 4

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.

Question 5

In Comptons equation for the change in wavelength of the x-ray photon, what is 0 equal to when trying to maximize?

Answer 5

0 = 180 degrees

Question 6

Describe the Compton scattering Experiment? Draw the apparatus.

Answer 6

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.

Question 7

What does it mean if a collision is elastic?

Answer 7

NET momentum and NET kinetic energy are conserved

Question 8

Derive the equations Compton discovered when using the conservation of energy and conservation of momentum.

Answer 8

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

Question 9

Use the equations for momentum and E=mc^2 to prove that a photon can have momentum.

Answer 9

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/~

Question 10

What is light spectra?

Answer 10

Coloured patterns produced when light is either dispersed through an equilateral glass prism or spread apart by a diffraction grating.

Question 11

How is a continuous spectra produced?

Answer 11

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)

Question 12

Describe the Franck-Hertz Experiment. Explain the observations and conclusions.

Answer 12

• 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

Question 13

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)

Answer 13

(1) a ground state(lowest energy state)
(2) an excited energy state
(3) exist in intermediate states

Question 14

What happens when an electron drops to a lower excitation state?

Answer 14

Energy is released in the form of a photon. Franck and Hertz then measured the wavelength of light emitted by the excited mercury atoms.

Question 15

What is ionization energy?

Answer 15

The amount of energy required to force an electron to leave the atom(when n= infinity)

Question 16

What is the ground state?

Answer 16

The lowest possible energy state that an electron can exist in.

Question 17

What is the emission or bring line spectra?

Answer 17

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

Question 18

What is the absorption or dark line spectrum?

Answer 18

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.

Question 19

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)?

Answer 19

(1/~) = R(H) ((1/2^2) - (1-n^2))

R(H) = 1.097 x 10^7 m^-1
n starts at 3

Question 20

How do a wave and particle differ?

Answer 20

Wave: Continuous, diffraction, interference, polarization
Particle: Discrete, has mass os it also has momentum

Question 21

How does an electron and photon differ?

Answer 21

An electron has mass and charge while a photon has no mass and no charge.

Question 22

How are absorption spectra created?

Answer 22

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.

Question 23

How is an emission spectrum created?

Answer 23

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.

Question 24

Who was Niels Bohr? What did Bohr predict?

Answer 24

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

Question 25

What were Bohr’s 3 postulations?

Answer 25

1. In a specific excitation state, electrons move in circular orbits called stationary states, but they do not radiate energy
2. Of all possible orbits around the nucleus, only a few are allowed. Each orbit has a characteristic radius and energy
3. Electrons can jump from one orbit to another, but cannot exist between them.(This is why spiralling can not occur, electrons can’t just exist anywhere)

Question 26

What were the limitations on de Broglie’s wavelength equation?

Answer 26

Particles with large masses have wavelengths that are too small to ever allow for diffraction and interference.

Question 27

What was the Davison-Germer experiment?

Answer 27

-Experimentally proved de Broglie’s hypothesis by firing electrons through a nickel crystal
- Array of atoms in the crystal act as a diffraction grating which cause electrons to diffract and form an interference pattern

Question 28

Who was Louis de Broglie? What did he hypothesize and what equation did he discover?

Answer 28

Wondered if subatomic particles(i.e. the electron) could exhibit wave-like properties.

Hypothesized that anything that has momentum also has a corresponding wavelength.

Particle: p = mv(*)

photon: p = h/~(**)

(*) = (**)

mv = h/~

~ = h/mv

h must be in Jxs
m must be in kg
v must be in m/s

Question 29

Describe the phenomenon of orbiting electron waves.

Answer 29

de Broglie applied the wave nature of an electron to an electron orbiting around a hydrogen nuclei. He predicted that the electron acts like a standing wave spread out over a circular orbit of radius r

Question 30

An electron wave that closes on itself will ___________________(1) to produce a ____________________(2). This occurs ____________________________(3). This explains why there are only __________________(4)

Answer 30

(1) constructively interfere
(2) stable standing wave
(3) who the circumference of the circular orbit(2(pi)r) contains a natural number of wavelength(n~)
(4) discrete energy levels

Question 31

If (trident) represents the ______________________(1) of the electron wave, then (trident squared) at a __________________(2) represents ______________________(3)

Answer 31

(1) amplitude
(2) given position in time
(30 the probability of finding the electron at that given position in time

Question 32

derive the equation for electron waves

Answer 32

2(pi) r = n~
2(pi)r = n(h/(mv))
mvr = n(h/(2(pi)))

n is the number of wavelengths at the nth stationary state

Question 33

What is the formula for radius(and value of r1) and ionization energy(and E1) for an electrons orbit?

Answer 33

refer to book

Question 34

The energy emitted/absorbed when an electron jumps from an excitation state has a frequency and wavelength determined by?