Chapter 30: Light Emission

Question 1

Light from a lit match comes from

Answer 1

electrons.

Question 2

A pulse of electromagnetic radiation is called a

Answer 2

photon.

Question 3

Atoms of neon in a glass tube can be excited

Answer 3

over and over again.

Question 4

The dark lines in the sun’s spectrum represent light that is: a) absorbed by the Sun’s atmosphere; b) emitted by the Sun; c) too hot to leave the surface of the Sun.

Answer 4

a) absorbed by the Sun’s atmosphere.

Question 5

Astronomers can tell whether a star is approaching or receding from Earth by: a) its temperature; b) its change in temperature; c) its absorption spectra; d) the Doppler effect.

Answer 5

d) the Doppler effect.

Question 6

Light from a laser is: a) monochromatic; b) in phase; c) coherent; d) all of these.

Answer 6

d) all of these.

Question 7

The photon of which radiation has the highest energy: a) blue light; b) green light; c) yellow light; d) orange light; e) red light.

Answer 7

a) blue light.

Question 8

The Sun does not have a continuous spectrum because: a) it is too far away from us; b) some of the light frequencies are absorbed by cool gases; c) only certain frequencies of radiation are emitted in the Sun’s inferno; d) the Sun’s energy is not converted to light; e) trick question: the Sun has a continuous spectrum.

Answer 8

b) some of the light frequencies are absorbed by cool gases.

Question 9

LED lights emit light when: a) electrons change energy levels; b) photons are created from phosphors; c) atoms remain in a metastable state; d) tungsten is heated and glows.

Answer 9

a) electrons change energy levels.

Question 10

An excited atom is an atom: a) that has excess vibration; b) that has one or more displaced electrons; c) with more protons than electrons; d) that is frantic.

Answer 10

b) that has one or more displaced electrons.

Question 11

Ultraviolet light is

Answer 11

electromagnetic energy.

Question 12

To say that energy levels in an atom are discrete is to say the energy levels are well defined and

Answer 12

separate from one another.

Question 13

Electrons with the greater potential energies with respect to the atomic nucleus are

Answer 13

outer electrons.

Question 14

Spectral lines take the shape of vertical lines because: a) the light is vertically polarized; b) they are simply images of a vertical slit; c) the energy levels in the atom are parallel to one another.

Answer 14

b) they are simply images of a vertical slit.

Question 15

Which light source is more energy-efficient: a) a fluorescent lamp; b) an incandescent lamp.

Answer 15

a) a fluorescent lamp.

Question 16

Helium was first discovered in the

Answer 16

sun.

Question 17

Light frequency from an incandescent lamp depends on the: a) amount of electrical energy transformed; b) rate of atomic and molecular vibrations; c) voltage applied to the lamp; d) electrical resistance of the lamp; e) transparency of glass.

Answer 17

b) rate of atomic and molecular vibrations.

Question 18

The greater proportion of energy immediately converted to heat rather than light occurs in: a) a fluorescent lamp; b) an incandescent lamp.

Answer 18

b) an incandescent lamp.

Question 19

The white light emitted by a fluorescent lamp is provided by the: a) mercury vapor in the lamp; b) phosphors on the inner surface of the lamp; c) high temperature of the glowing gas; d) filtering effect of the glass tubing.

Answer 19

b) phosphors on the inner surface of the lamp.

Question 20

The variety of colors seen in a burning log comes from the variety of: a) multi-layered incandescent surfaces; b) electron transitions in various atoms; c) temperatures; d) chemicals in the log; e) absorbing gases between the log and the viewer.

Answer 20

b) electron transitions in various atoms.

Question 21

The process of separation of light into colors arranged by frequency​ is

Answer 21

dispersion.

Components of white light are dispersed in a prism (and in a diffraction grating).​

Question 22

When white light passes through a prism, green light is bent more than​: a) blue light; b) violet light; c) red light; d) None of the above.

Answer 22

c) red light.

Question 23

Sunlight incident on two raindrops, emerges from them as dispersed light. ​The observer sees the red light from the _____ drop and the violet light from the _____ drop. ​

Answer 23

Blank 1: upper
Blank 2: lower

Millions of drops produce the whole spectrum of visible light.​

Question 24

________ are a result of dispersion by many raindrops.

Answer 24

Rainbows

Question 25

All the drops that disperse the rainbow’s light toward you lie in the shape of a ____.

Answer 25

cone;

A cone of different layers with drops that disperse red to your eye on the outside, orange beneath the red, yellow beneath the orange, and so on, all the way to violet on the inner conical surface. ​

Question 26

The thicker the region containing water drops, the thicker the conical edge you look through, and the more _____ the rainbow.​

Answer 26

vivid

Question 27

Compared with the primary rainbow, the secondary bow​: a) is dimmer; b) has colors reversed; c) is caused by two internal reflections; d) All of the above.​
​

Answer 27

d) All of the above.​

Question 28

Secondary rainbow​s are _______ and reversed in _____. ​

Answer 28

Blank 1: fainter
Blank 2: color

This is due to two internal reflections and refracted light loss​ and due to the extra internal reflection.​

Question 29

The first droplet from above that can disperse the light into your eyes must be its least _______ light.

Answer 29

bending; (red light​)

Question 30

Excitation is the process in which​: a) electrons are boosted to higher energy levels in an atom; b) atoms are charged with light energy; c) atoms are made to shake, rattle, and roll; d) None of the above.​
​
​

Answer 30

a) electrons are boosted to higher energy levels in an atom.

Question 31

Which has less energy per photon: a) Red light​; b) Green light; c) Blue light​; d) All have the same.​

Answer 31

a) Red light.

In accord with E ~ f, the lowest-frequency light has the lowest energy per photon.​ The frequency of an emitted photon ~ energy-level difference in de-exciting:​ E = hf
h: Planck constant​

Question 32

Discrete states are _______ states​.

Answer 32

quantum;

These states are found only at certain energies; we say they are discrete.

Question 33

Most of what we know about atoms is gained by investigating the​: a) masses of elements; b) electric charge of elements; c) periodic table of the elements; d) light they emit.​

Answer 33

d) light they emit.​

Light emitted by atoms, their atomic spectra, are considered to be the fingerprints of atoms.​

Question 34

An atom that absorbs a photon can then emit one​: a) only at the same energy; b) of any energy depending on the situation; c) only at a higher energy; d) only at the same or lower energy.​
​

Answer 34

d) only at the same or lower energy.​