Question 1

The wavelength of the red-pink line emitted by a laboratory sample of excited hydrogen is 656 nm. Taking a spectrum of a glowing nebula, you find that the same red-pink line of hydrogen appears at 662 nm. You conclude that the nebula

Accepted Answer

The increase in wavelength from 656 nm to 662 nm indicates a redshift, which means the nebula is moving away from us. The change in wavelength suggests a velocity of about 1% the speed of light.

Question 2

As a body cools, its spectrum will shift to ____ wavelengths.

Accepted Answer

As a body cools, it emits radiation at longer wavelengths according to Wien's Displacement Law, which states that the peak wavelength of emission is inversely proportional to the temperature.

Question 3

Which of these are effects of the Doppler shift?

Accepted Answer

The Doppler shift causes the wavelengths of light to decrease (blue shift) when an object is moving toward us, and increase (red shift) when moving away.

Question 4

As a body heats, the radiation it emits _______________.

Accepted Answer

As a body heats, it emits radiation that peaks at a shorter wavelength according to Wien's Law, which states that the peak wavelength is inversely proportional to the temperature.

Question 5

The lower the frequency of the electromagnetic wave, the shorter its wavelength.

Accepted Answer

The wavelength of an electromagnetic wave is inversely proportional to its frequency. Therefore, a lower frequency means a longer wavelength, not shorter.

Question 6

A temperature of 0 Kelvin means there is essentially no motion at the atomic level.

Accepted Answer

At 0 Kelvin, also known as absolute zero, atoms are at their lowest energy state, and theoretically, all motion stops.

Question 7

A piece of iron heated to 200 degrees Celsius has twice as much internal energy as a piece of iron at 100 degrees Celsius.

Accepted Answer

The internal energy of a substance depends on its temperature, mass, and specific heat capacity, not just temperature alone. Doubling the temperature in Celsius does not double the internal energy.

Question 8

A continuous blackbody spectrum provides information about the surface temperature of the object.

Accepted Answer

A continuous blackbody spectrum is determined by the temperature of the object, allowing us to infer the surface temperature based on the peak wavelength or intensity distribution.

Question 9

Scientist use the term "blackbody" to indicate a surface that will not emit any color of visible light.

Accepted Answer

A blackbody is an idealized physical object that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence, and emits radiation in a characteristic continuous spectrum that depends only on the body's temperature.

Question 10

According to Wien's law, the dominant wavelength in the continuous emission spectrum of a red apple is 700 nm. (Hint: use Wien's law.)

Accepted Answer

Wien's law applies to blackbody radiation, not to the color of objects like a red apple, which reflects specific wavelengths rather than emitting them.

Question 11

Cooler stars (about 3000 K) emit most of their radiation at wavelengths shorter than 600 nm.

Accepted Answer

Cooler stars emit most of their radiation at longer wavelengths, typically in the infrared range, not shorter than 600 nm.

Question 12

The color of a yellow banana is a result of blackbody emission.

Accepted Answer

The color of a yellow banana is due to the reflection of specific wavelengths of light by pigments in the banana's skin, not blackbody emission.

Question 13

An atom with 6 protons and 6 neutrons is a carbon atom, and an atom with 6 protons and 7 neutrons is also a carbon atom.

Accepted Answer

Atoms with the same number of protons but different numbers of neutrons are isotopes. Both atoms have 6 protons, which makes them carbon, but they are different isotopes: Carbon-12 and Carbon-13.

Question 14

When an atom absorbs energy it becomes excited.

Accepted Answer

When an atom absorbs energy, its electrons can move to higher energy levels, putting the atom in an excited state.

Question 15

When an atom emits light, an electron in it moves from a higher to a lower energy level.

Accepted Answer

When an atom emits light, it releases energy as an electron transitions from a higher energy level to a lower one, resulting in the emission of a photon.

Question 16

You are heating a jar full of hydrogen and observing its spectrum. If you add more hydrogen to the jar, the position of spectral lines will change.

Accepted Answer

The position of spectral lines is determined by the energy levels of the hydrogen atoms, which do not change with the amount of hydrogen present. Adding more hydrogen increases the intensity of the lines but not their position.

Question 17

By studying the continuous blackbody spectrum from a solid it is possible to deduce the composition of the solid.

Accepted Answer

The continuous blackbody spectrum only provides information about the temperature of the solid, not its composition.

Question 18

An X-ray telescope placed on the surface of Earth can detect X-rays that are emitted from a distant astrophysical source.

Accepted Answer

X-rays are absorbed by Earth's atmosphere, so X-ray telescopes need to be placed in space to detect X-rays from astrophysical sources.

Question 19

The Doppler shift is the same if the emitting object is moving toward you at some speed, or you (the observer) are moving toward it at that speed and it is still.

Accepted Answer

The Doppler shift depends only on the relative velocity between the source and the observer, not on which one is moving.

Question 20

The Doppler shift applies only to the line spectrum. It does not apply to the continuous (blackbody) spectrum.

Accepted Answer

The Doppler shift affects all types of electromagnetic radiation, including both line and continuous spectra, by altering the observed frequency or wavelength due to relative motion between the source and observer.

Quiz 4: Light and Atoms