TEST 3

Question 1

What is a wave?

Answer 1

A wave is an oscillation or periodic movement that can transport energy from one point in space to another. (kinetic energy is transferred through matter (the rope, water, or air) while the matter remains essentially in place.)

Question 2

electromagnetic waves consist of

Answer 2

an electric field oscillating in step with a perpendicular magnetic field, both of which are perpendicular to the direction of travel. These waves can travel through a vacuum at a constant speed of 2.998 × 10^8 m/s, the speed of light (denoted by c)

Question 3

waves are characterized by

Answer 3

a wavelength, a frequency and an amplitude

Question 4

wavelength

Answer 4

lamda; the distance between two consecutive peaks or troughs in a wave measured in meters

Question 5

frequency

Answer 5

Hz, v or nu; the number of wave cycles that pass a specified point in space in a specified amount of time (seconds.) A cycle corresponds to one complete wavelength.

Question 6

amplitude

Answer 6

corresponds to the magnitude of the wave’s displacement. The amplitude is related to the intensity of the wave, which for light is the brightness, and for sound is the loudness.

Question 7

speed of a wave

Answer 7

The product of a wave’s wavelength (λ) and its frequency (ν

Question 8

for electromagnetic radiation in a vacuum, speed is equal to

Answer 8

the fundamental constant, c

Question 9

what is the relationship between wavelength and frequency

Answer 9

inversely proportional. As the wavelength increases, the frequency decreases.

Question 10

what happens when two or more waves come into contact?

Answer 10

they interfere with one another

Question 11

standing waves

Answer 11

remain constrained within some region of space. A system with fixed end points such as this restricts the number and type of the possible waveforms. This is an example of quantization, in which only discrete values from a more general set of continuous values of some property are observed.

Question 12

nodes

Answer 12

waves displaying more than one-half wavelength) all have one or more points between the two end points that are not in motion called nodes. number of nodes= n-1

Question 13

what is a blackbody?

Answer 13

A blackbody is a convenient, ideal emitter that approximates the behavior of many materials when heated. It is “ideal” in the same sense that an ideal gas is a convenient, simple representation of real gases that works well, provided that the pressure is not too high nor the temperature too low. BUT the theoretical curves did not show a peak, and absurdly showed the intensity becoming infinitely large as the wavelength became smaller, which would imply that everyday objects at room temperature should be emitting large amounts of UV light. This became known as the “ultraviolet catastrophe” Planck resolved this by restricting the vibrational energies to discrete values for each frequency, he could derive an expression for blackbody radiation that correctly had the intensity dropping rapidly for the short wavelengths in the UV region.

Question 14

E=

Answer 14

hc/lamda

Question 15

Planck’s constant (a.k.a. h)

Answer 15

h= 6.626 ×× 10−34 joule seconds (J s)

Question 16

a wave’s energy depends on its

Answer 16

intensity (which depends on the number of photons striking the surface within a given time period.) bc the number of electrons ejected within in a given time period was seen to increase as the brightness increased. So, the greater the number of incoming photons, the greater the likelihood that they would collide with some of the electrons.

Question 17

increasing the brightness of incoming light ____ the number of ejected electrons

Answer 17

increases

Question 18

increasing the frequency of incoming light can ____ the number of ejected electrons

Answer 18

increase

Question 19

does increasing the brightness of light have an effect on the KE of the ejected electrons?

Answer 19

Increasing the brightness of incoming light has no effect on the kinetic energy of the ejected electrons. Only energy, not the number or amplitude, of the photons influences the kinetic energy of the electrons.

Question 20

increasing the frequency of incoming light ___ the KE of the ejected electrons

Answer 20

increases. Frequency is proportional to energy and inversely proportional to wavelength. Frequencies above the threshold value transfer the excess energy into the kinetic energy of the electrons.

Question 21

energy of an electron

Answer 21

𝐸=−𝑘𝑍^2/𝑛2

Question 22

when an electron increases distance from the nucleus, it’s energy ___

Answer 22

increases

Question 23

The discrete energies (lines) in the spectra of the elements result from

Answer 23

quantized electronic energies.

Question 24

The energies of electrons (energy levels) in an atom are described by

Answer 24

quantum numbers: integer numbers having only specific allowed value and used to characterize the arrangement of electrons in an atom.

Question 25

the intensity of a wave is related to its ____

Answer 25

amplitude

Question 26

speed of a wave can be calculated with

Answer 26

The product of a wave’s wavelength (λ) and its frequency (ν), λν, is the speed of the wave. Thus, for electromagnetic radiation in a vacuum, speed is equal to the fundamental constant, c.
c=λν

Question 27

einstein on the photoelectric effect

Answer 27

Einstein argued that the quantized energies that Planck had postulated in his treatment of blackbody radiation could be applied to the light in the photoelectric effect so that the light striking the metal surface should not be viewed as a wave, but instead as a stream of particles (later called photons) whose energy depended on their frequency, according to Planck’s formula, E = hν (or, in terms of wavelength using c = νλ, 𝐸=ℎ𝑐𝜆E=hcλ ). Electrons were ejected when hit by photons having sufficient energy (a frequency greater than the threshold). The greater the frequency, the greater the kinetic energy imparted to the escaping electrons by the collisions. Einstein also argued that the light intensity did not depend on the amplitude of the incoming wave, but instead corresponded to the number of photons striking the surface within a given time period. This explains why the number of ejected electrons increased with increasing brightness, since the greater the number of incoming photons, the greater the likelihood that they would collide with some of the electrons.

Question 28

photoelectric effect

Answer 28

electrons could be ejected from the clean surface of a metal when light having a frequency greater than some threshold frequency was shone on it. Surprisingly, the kinetic energy of the ejected electrons did not depend on the brightness of the light, but increased with increasing frequency of the light. Since the electrons in the metal had a certain amount of binding energy keeping them there, the incident light needed to have more energy to free the electrons. According to classical wave theory, a wave’s energy depends on its intensity (which depends on its amplitude), not its frequency.

Question 29

Each emission line consists of

Answer 29

a single wavelength of light, which implies that the light emitted by a gas consists of a set of discrete energies

Question 30

Johann Balmer was able to derive

Answer 30

an empirical equation that related the four visible wavelengths of light emitted by hydrogen atoms to whole integers.
1/λ=k(1/4 - 1/n^2)

Question 31

Johannes Rydberg

Answer 31

generalized Balmer’s work and developed an empirical formula that predicted all of hydrogen’s emission lines, not just those restricted to the visible range, where, n1 and n2 are integers, n1 < n2, and 𝑅∞R∞ is the Rydberg constant (1.097 ×× 107 m−1).

Question 32

bohr

Answer 32

as the electron’s energy increases (as n increases), the electron is found at greater distances from the nucleus.; derived a theoretical expression for the Rydberg constant,

Question 33

de Broglie argued that

Answer 33

Bohr’s assumption of quantization can be explained if the electron is considered not as a particle, but rather as a circular standing wave such that only an integer number of wavelengths could fit exactly within the orbit
2𝜋𝑟=𝑛𝜆

Question 34

Heisenberg uncertainty principle:

Answer 34

It is fundamentally impossible to determine simultaneously and exactly both the momentum and the position of a particle