Lesson 5

Question 1

If you have a 100-watt light bulb, how much energy does it use each minute?

Answer 1

6000 joules

Question 2

Everything looks red through a red filter because

Answer 2

the filter transmits red light and absorbs other colors.

Question 3

How are wavelength, frequency, and energy related for photons of light?

Answer 3

Longer wavelength means lower frequency and lower energy.

Question 4

From lowest energy to highest energy, which of the following correctly orders the different categories of electromagnetic radiation?

Answer 4

radio, infrared, visible light, ultraviolet, X rays, gamma rays

Question 5

From shortest to longest wavelength, which of the following correctly orders the different categories of electromagnetic radiation?

Answer 5

gamma rays, X rays, ultraviolet, visible light, infrared, radio

Question 6

How many atoms fit across the period at the end of this sentence?

Answer 6

millions

Question 7

Compared to the volume of its nucleus, the volume of an atom is about

Answer 7

a trillion times greater

Question 8

Suppose you built a scale-model atom in which the nucleus was the size of a tennis ball. About how far would the cloud of electrons extend?

Answer 8

several kilometers

Question 9

An atom of the element iron has an atomic number of 26 and an atomic weight of 56. If it is neutral, how many protons, neutrons, and electrons does it have?

Answer 9

26 protons, 30 neutrons, 26 electrons

Question 10

Sublimation is the process in which

Answer 10

molecules go from the solid phase to the gas phase

Question 11

An atom in an excited state contains more what type of energy than the same atom in the ground state?

Answer 11

electric potential energy

Question 12

An electron-volt is

Answer 12

an amount of energy much smaller than a joule.

Question 13

If you heat a gas so that collisions are continually bumping electrons to higher energy levels, when the electrons fall back to lower energy levels the gas produces

Answer 13

an emission line spectrum

Question 14

When white light passes through a cool cloud of gas, we see

Answer 14

an absorption line spectrum

Question 15

A perfectly opaque object that absorbs all radiation and reemits the absorbed energy as thermal radiation is

Answer 15

a thermal emitter

Question 16

If two objects are the same size but one object is 3 times hotter than the other object, the hotter object emits

Answer 16

81 times more energy.

Question 17

We can learn a lot about the properties of a star by studying its spectrum. All of the following statements are true except one. Which one?

Answer 17

The total amount of light in the spectrum tells us the star’s radius.

Question 18

From laboratory measurements, we know that a particular spectral line formed by hydrogen appears at a wavelength of 486.1 nanometers (nm). The spectrum of a particular star shows the same hydrogen line appearing at a wavelength of 485.9 nm. What can we conclude?

Answer 18

The star is moving toward us.

Question 19

You observe a distant galaxy. You find that a spectral line normally found in the visible part of the spectrum is shifted toward the infrared. What do you conclude?

Answer 19

The galaxy is moving away from you

Question 20

Visible light from a distant star can be spread into a spectrum by using a glass prism or

Answer 20

a diffraction grating

Question 21

Suppose you look at a spectrum of visible light by looking through a prism or diffraction grating. How can you decide whether it is an emission line spectrum or an absorption line spectrum?

Answer 21

An emission line spectrum consists of bright lines on a dark background, while an absorption line spectrum consists of dark lines on a rainbow background.

Question 22

Suppose that two stars are identical in every way—for example, same distance, same mass, same temperature, same chemical composition, and same speed relative to Earth—except that one star rotates faster than the other. Spectroscopically, how could you tell the stars apart?

Answer 22

The faster rotating star has wider spectral lines than the slower rotating star.