Question 1

Describe,in your own words,the fundamental problem with the Bohr model of the atom.(That is,why doesn't an electron orbit a nucleus like a planet does the Sun?)

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Question 2

The average red giant in the night sky is about 1,000 times more luminous than the average main-sequence star.If both kinds of stars have about the same brightness,how much farther away are the red giants compared to the main-sequence stars?

Accepted Answer

The luminosity of a star is proportional to the square of its distance if the brightness is the same. Therefore, the distance ratio is the square root of the luminosity ratio: √1000 ≈ 32.

Question 3

At what temperature does water freeze?

Accepted Answer

Water freezes at 0 degrees Celsius, which is equivalent to 273 Kelvin. Therefore, the answer choice is 273 K.

Question 4

An asteroid with an albedo of 0.1 and a comet with an albedo of 0.6 are orbiting at roughly the same distance from the Sun.How do their temperatures compare?

Accepted Answer

The albedo of an object is a measure of how reflective it is. An object with a high albedo (like the comet with an albedo of 0.6) reflects more sunlight and absorbs less, therefore, it would have a lower temperature than an object with a low albedo (like the asteroid with an albedo of 0.1), which absorbs more sunlight and reflects less. Therefore, the asteroid would be hotter than the comet in this scenario.

Question 5

Star C and star D are equally luminous.Star C is twice as far away from Earth as star D.How do the brightness level of stars C and D compare?

Accepted Answer

The brightness of a star as seen from Earth is inversely proportional to the square of its distance. Since star C is twice as far away as star D, it will appear 1/(2^2) = 1/4 as bright as star D. Thus, star D appears four times as bright as star C.

Question 6

At what wavelength does your body radiate the most given that your temperature is approximately that of the Earth,which is 300 K?

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Question 7

Which of the following factors does NOT directly influence the temperature of a planet?

Accepted Answer

The size of the planet does not directly influence its temperature. A planet's temperature is mainly determined by its distance from the Sun, the amount of solar radiation it receives, and the planet's ability to retain and radiate that heat back out into space, which is influenced by factors like its atmosphere and albedo.

Question 8

Name four physical properties of an object that we can determine by analyzing the radiation that it emits,and briefly describe how these properties are determined.Cite the names of any laws that apply.

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Question 9

As a blackbody becomes hotter,it also becomes __________ and __________.

Accepted Answer

As a blackbody becomes hotter, it emits more energy at shorter wavelengths, causing it to be bluer in color. At the same time, it becomes more luminous because it is emitting more energy overall. Therefore, Option B (more luminous; bluer) is the correct answer.

Question 10

The difference in energy between the  and  electronic energy levels in the hydrogen atom is  .If an electron moves from the  level to the  level will a photon be emitted or absorbed? What will its energy be,and what type of electromagnetic radiation is it?

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Question 11

You record the spectrum of a star and find that the calcium absorption line,whose rest wavelength is 393.3 nm,has an observed wavelength of 394.0 nm.What is the radial velocity of this star?

Accepted Answer

The radial velocity of the star can be calculated using the formula:$$v = c * (lambda_o - lambda_e) / lambda_o$$where:* v is the radial velocity* c is the speed of light* lambda_o is the rest wavelength* lambda_e is the observed wavelengthSubstituting the given values into the formula, we get:$$v = 3 * 10^8 m/s * (393.3 nm - 394.0 nm) / 393.3 nm$$$$v = -500 km/s$$The negative sign indicates that the star is moving away from us.

Question 12

The Kelvin temperature scale is used in astronomy because

Accepted Answer

The Kelvin temperature scale starts at Absolute Zero, which is the temperature at which an object has absolutely zero energy. This makes it a useful scale for measuring the temperature of objects in space, where temperatures can be extremely low. Option B and C refer to the Celsius temperature scale, while option D is not a correct statement.

Question 13

Consider an incandescent light bulb.If you wanted to turn a 10 W light bulb into a 100 W light bulb,how would you change the temperature of the filament inside the bulb?

Accepted Answer

The power output of an incandescent light bulb is proportional to the temperature of the filament raised to the fourth power. This means that if we want to increase the power output by a factor of 10 (from 10 W to 100 W), we need to increase the temperature of the filament by a factor of the 4th root of 10, which is about 1.8. Therefore, we would need to raise the temperature of the filament by a factor of 1.8 to turn a 10 W light bulb into a 100 W light bulb.

Question 14

A spaceship approaches Earth at 0.9 times the speed of light and shines a powerful searchlight onto Earth.How fast will the photons from this searchlight be moving when they hit Earth?

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Question 15

Star A and star B appear equally bright in the sky.Star A is twice as far away from Earth as star B.How do the luminosities of stars A and B compare?

Accepted Answer

Star A must be four times as luminous as star B to appear equally bright despite being twice as far away, due to the inverse square law of light.

Question 16

What is the surface temperature of a star that has a peak wavelength of 290 nm?

Accepted Answer

The peak wavelength of a star's radiation spectrum is related to its surface temperature by Wien's law, which states:

λmaxT = 2.898 × 10^−3 m K

where λmax is the peak wavelength in meters and T is the surface temperature in kelvin. Converting 290 nm to meters gives:

λmax = 290 × 10^−9 m

Substituting into the equation and solving for T gives:

T = 2.898 × 10^−3 m K / (290 × 10^−9 m) = 10,000 K

Therefore, the surface temperature of the star is 10,000 K, which corresponds to answer choice D.

Question 17

Compare and contrast the wavelengths,frequencies,speeds,and energies of red and blue photons.

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Question 18

Compare two blackbody objects,one at 200 K and one at 400 K.How much larger is the flux from the 400 K object,compared to the flux from the 200 K object?

Accepted Answer

The flux of a blackbody is proportional to the fourth power of its temperature (Stefan-Boltzmann law). Therefore, the ratio of fluxes between two blackbodies at temperatures T1 and T2 is (T2/T1)^4. In this case, we have T1 = 200 K and T2 = 400 K, so the ratio of fluxes is (400/200)^4 = 16. Therefore, the flux from the 400 K object is 16 times larger than the flux from the 200 K object.

Question 19

A black car left in the sunlight becomes hotter than a white car left in the sunlight under the same conditions because

Accepted Answer

The reason why the black car is hotter than the white car is due to the fact that it absorbs more sunlight. Darker colors absorb more light and as a result, convert more of that light into heat energy. White, on the other hand, reflects more light, resulting in less heat absorbed by the car. Therefore, option B is the correct answer.

Question 20

If Saturn has a semimajor axis of 10 AU and an albedo of 0.7,what is its expected temperature?

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Quiz 4: Light