hw 2 (photons, photoelectric effect, de Broglie wavelength, Bohr model)

Question 1

If the amplitude of a electromagnetic wave increases, the frequency will _____.

Answer 1

stay the same

Question 2

If the amplitude of a electromagnetic wave increases, the wavelength will _____.

Answer 2

stay the same

Question 3

If the frequency of a electromagnetic wave decreases, the amplitude will _____.

Answer 3

stay the same

Question 4

If the frequency of a electromagnetic wave increases, the wavelength will _____.

Answer 4

decrease

Question 5

If the wavelength of a electromagnetic wave decreases, the amplitude will _____.

Answer 5

stay the same

Question 6

If the wavelength of a electromagnetic wave decreases, the frequency will _____.

Answer 6

increase

Question 7

Einstein’s work on the photoelectric effect validated and made extensive use of which of the following equations?

Answer 7

Einstein’s achievements with the photoelectric effect proved that photons of sufficient energy were necessary to remove electrons from metal upon which they were shone. As a result, he made extensive use of the equation E=hν, which quantifies the energy (E) of a photon based on its frequency (ν) and Planck’s constant (h).

Question 8

If light has a lot of energy, it will have:

Answer 8

A small wavelength

Question 9

Photons are shone on a piece of metal and one electron is ejected for each absorbed photon. What happens when the wavelength of light is decreased?

Answer 9

Decreasing the wavelength (λ) of the light increases its energy, meaning that the electrons will be ejected with a greater kinetic energy (KE).

Question 10

Excited hydrogen atoms emit radiation in which region(s) of the electromagnetic spectrum?

Answer 10

Excited hydrogen atoms are capable of emitting radiation with wavelengths from 100 nm to 10,000 nm; this section of the electromagnetic spectrum includes IR, visible, and UV radiation.

Question 11

What is observed when a noble gas is heated and the emitted light shone through a prism?

Answer 11

Heating a noble gas promotes its electrons to excited energy states, which then relax to emit discrete wavelengths of light. When shone through a prism, this results in individual lines of varying colors.

Question 12

In the Bohr model of the hydrogen atom, the energy required to excite an electron from n = 2 to n = 3 is _______________ the energy required to excite an electron from n = 3 to n = 4

Answer 12

greater than

Question 13

If the electron is dropping to n=1, which transition will emit the longest wavelength? n=______ to n=1.

Answer 13

2

Question 14

Planck’s observations that wavelengths increase as objects cool down did not hold up for objects at room temperature. He proposed restricting the vibrational energies to discrete values for each frequency.

This expression is

Answer 14

E = nhv

Question 15

Planck observed that light is emitted in a metal oven heated to high temperatures. The wavelength (λmax) of the light shifts to _______ wavelengths as the temperature increases.

Answer 15

shorter

Question 16

When light shines on a metal, electrons can be ejected from the surface of the metal in “the photoelectric effect”. Experiments showed that the wavelength of light is inversely proportional to kinetic energy of the electrons ejected.
Identify the best explanation of the photoelectric effect.

Answer 16

Increasing the frequency of the incoming light increases the energy of the ejected electrons. Remember, frequency is proportional to energy so this is increasing the energy of the incoming light.

Question 17

Einstein modified Planck’s equation to assume that the light consisted of quantized particles (photons) and the energy was dependent upon their wavelength.

What is the equation that he developed for this relationship?

Answer 17

E = hc/λ

Question 18

A student was doing an experiment on the photoelectric effect. She used a light source to eject electrons from the metal source. The student continuously irradiated the same area of the metal for a long time and she noticed the maximum kinetic energy of ejected electrons began to decrease, even though the frequency of the light was constant. Choose the best explanation for this observation.

Answer 18

As the electrons are ejected, the metal becomes positively charged, attracting the recently ejected electrons back toward the metal.