Ch 5 Concept Quiz study

Suppose a photon has a frequency of 300 million hertz (300 megahertz). What is its wavelength?

1 meter -Frequency is related to wavelength by the formula: wavelength ( frequency = speed of light = 300 million m/s. Thus, for a frequency of 300 million hertz, the wavelength is 1 meter, since 1 m ( 300 million /s = 300 million m/s.

Suppose you have a 100-watt light bulb that you leave turned on for one minute. How much energy does it use?

6,000 joules -To find this answer, remember that 1 watt = 1 joule/s, so a 100-watt light bulb uses 100 joules of energy per second. In 1 minute, it uses 60 ( 100 = 6,000 joules of energy.

Which of the following statements about thermal radiation is always true?

A hot object emits more radiation per unit surface area than a cool object. -This is part of the first law of thermal radiation (the Stefan-Boltzmann law).

Each of the following describes an "Atom 1" and an "Atom 2." In which case are the two atoms different isotopes of the same element?

Atom 1: nucleus with 7 protons and 8 neutrons, surrounded by 7 electrons; Atom 2: nucleus with 7 protons and 7 neutrons, surrounded by 7 electrons -They are isotopes both atoms have the same atomic number but different atomic mass numbers.

Consider an atom of oxygen in which the nucleus contains 8 protons and 8 neutrons. If it is doubly ionized, what is the charge of the oxygen ion and how many electrons remain in the ion?

Charge = +2; number of remaining electrons = 6. -Because oxygen has 8 protons, it must also have 8 electrons when it is neutral. Doubly ionized means two electrons are missing, leaving only 6 electrons and an overall charge of 8-6= +2.

Which of the following statements about electrons is not true?

Electrons orbit the nucleus rather like planets orbiting the Sun. -Electrons are not much like tiny planets at all.

Which of the following statements is true of green grass?

It absorbs red light and reflects green light. -We see the reflected green light.

Suppose you had molecular oxygen (O2) chilled enough so that it was in liquid form. Which of the following best describes the phase changes that would occur as you heated the liquid oxygen to high temperature?

It would evaporate into a gas, then the molecules would dissociate into individual oxygen atoms, then the atoms would become increasingly ionized as you continued to raise the temperature.

Betelgeuse is the bright red star representing the left shoulder of the constellation Orion. All the following statements about Betelgeuse are true. Which one can you infer from its red color?

Its surface is cooler than the surface of the Sun. -Red light has lower energy than yellow or white light, so the red color of Betelgeuse tells us that its peak thermal radiation comes at lower energy than the peak thermal radiation of the yellow/white Sun. A lower energy of peak radiation means a lower temperature.

Suppose that Star X and Star Y both have redshifts, but Star X has a larger redshift than Star Y. What can you conclude?

Star X is moving away from us faster than Star Y. -The redshifts mean that both stars are moving away from us, and a larger redshift means a faster speed.

Which of the following conditions lead you to see an absorption line spectrum from a cloud of gas in interstellar space?

The cloud is cool and lies between you and a hot star. -Atoms or molecules in the cloud therefore absorb specific wavelengths of light from the hot star.

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?

The faster rotating star has wider spectral lines than the slower rotating star. -Fast rotation will widen spectral lines because there is a greater difference in the Doppler shift from the side of the star rotating toward us and the side rotating away from us.

Which of the following best describes why we say that light is an electromagnetic wave?

The passage of a light wave can cause electrically charged particles to move up and down. -That is, electrically charged particles can respond to (or generate) electromagnetic radiation.

If we observe one edge of a planet to be redshifted and the opposite edge to be blueshifted, what can we conclude about the planet?

The planet is rotating. -We see a blueshift from the side rotating toward us and a redshift from the side rotating away.

Suppose you are listening to a radio station that broadcasts at a frequency of 97 Mhz (megahertz). Which of the following statements is true?

The radio waves from the radio station are causing electrons in your radio's antenna to move up and down 97 million times each second. -That is how the antenna receives the signal from the radio station.

Laboratory measurements show hydrogen produces a spectral line at a wavelength of 486.1 nanometers (nm). A particular star's spectrum shows the same hydrogen line at a wavelength of 486.0 nm. What can we conclude?

The star is moving toward us. -The wavelength is shifted from 486.1 to 486.0 nm, which means a shift to a shorter wavelength. A shorter wavelength means a shift to the blue end of the spectrum (a blueshift) so that the object is moving toward us.

All of the following statements about the Sun's corona are true. Which one explains why it is a source of X rays?

The temperature of the corona's gas is some 1 to 2 million Kelvin. -The corona produces high-energy light (X rays) because of its high temperature.

Studying a spectrum from a star can tell us a lot. All of the following statements are true except one. Which statement is not true?

The total amount of light in the spectrum tells us the star's radius. -We cannot measure radius from a spectrum without additional information.

The planet Neptune is blue in color. How would you expect the spectrum of visible light from Neptune to be different from the visible-light spectrum of the Sun?

The two spectra would have similar shapes, except Neptune's spectrum would be missing a big chunk of the red light that is present in the Sun's spectrum. -The planets shine with reflected sunlight, so we'd essentially see the Sun's spectrum, minus the light absorbed by Neptune. Because Neptune looks blue, it must be absorbing red light.

Which of the following statements about X rays and radio waves is not true?

X rays travel through space faster than radio waves. -This is the right answer, because the statement is not true. All light travels at the same speed, so radio waves and X rays travel at the same speed.

No object produces a perfect thermal radiation spectrum, but many objects produce close approximations. Which of the following would not produce a close approximation to a thermal radiation spectrum?

a hot, thin (low-density, nearly transparent) gas -Photons must be able to bounce randomly around inside an object to produce thermal radiation, and that is not the case with a thin cloud of gas.

Gamma rays have a very small ______.

wavelength -Gamma rays are the highest-energy form of light, which means short wavelength and high frequency.