Open Stax Astronomy - CH5

Explain the evidence for Maxwell's electromagnetic model of light

After calculating the speed at which an electromagnetic disturbance moves through space; Maxwell found that it is equal to the speed of light, which had been measured experimentally.

On that basis, he speculated that light was one form of a family of possible electromagnetic disturbances called electromagnetic radiation.

Describe the relationship between wavelength, frequency, and speed of light

a. The wavelength (λ) is the distance between crests

b. The frequency (f) is the number of cycles per second

c. The speed (c) is the distance the wave covers during a specified period of time (e.g., kilometers per second).

Discuss the particle model of light and the definition of photon

a. The particle model of light was introduced because sometimes light behaves more like a "particle", or at least a self-contained packet of energy than a wave. Its essential theory was further evolved from electromagnetics into quantum mechanics.

b. Photon, a self-contained packet of energy

What distinguishes one type of electromagnetic radiation from another? What are the main categories (or bands) of the electromagnetic spectrum?

The "colors" of the electromagnetic spectrum can be distinguished by any one of the following quantitative variables:
wavelength (8); or frequency (<); or energy (E).

Once a number has been assigned to any one of these variables, the values of the other quantities can be calculated.

The main bands of the electromagnetic spectrum starting with the most energetic photons are: Gamma Rays, X- Rays, Ultraviolet,, Optical, Infrared, Microwaves, and Radio waves.

What is a wave? Use the terms wavelength and frequency in your definition.

Waves are a disturbance and are measured by peak to peak, wavelength, and how often the wave repeats itself, frequency.

Where in an atom would you expect to find electrons? Protons? Neutrons?

=Electrons orbit the nucleus, which is the neutrons and protons together.

Explain how emission lines and absorption lines are formed. In what sorts of cosmic objects would you expect to see each?

A spectrum obtained as a result of emission of electromagnetic radiations of different wavelengths (or frequency) by the electrons which come to ground state from the excited state.

Explain how the Doppler effect works for sound waves and give some familiar examples.

Doppler effect is the compression or extension of a sound wave, which causes a change in its wavelength / frequency (and so its sound).

What kind of motion for a star does not produce a Doppler effect? Explain.

Doppler effect - It is defined as the effect produced by a moving source of waves in which there is an upward shift in frequency for observers, the source is moving towards and downward shift of frequency from which the source is moving away

Describe how Bohr's model used the work of Maxwell.

The model states that electrons in atoms move in circular orbits around a central nucleus and can only orbit stably in certain fixed circular orbits at a discrete set of distances from the nucleus.

Explain why light is referred to as electromagnetic radiation.

An Electromagnetic wave is caused due to the mutually perpendicular magnetic and electric field

Explain the difference between radiation as it is used in most everyday language and radiation as it is used in an astronomical context.

In everyday language, "radiation" is often used to describe certain kinds of energetic subatomic particles released by radioactive materials in our environment. Radiation, as used in this book, is a general term for waves (including light waves) that radiate outward from a source.

What are the differences between light waves and sound waves?

Light travels as transverse waves and can travel through a vacuum. Sound travels as longitudinal waves and needs to travel through a solid, liquid or gas: it cannot travel through a vacuum.

Which type of wave has a longer wavelength: AM radio waves (with frequencies in the kilohertz range) or FM radio waves (with frequencies in the megahertz range)? Explain.

AM waves have a longer wavelength.

Explain why astronomers long ago believed that space must be filled with some kind of substance (the "aether") instead of the vacuum we know it is today.

Electromagnetic waves do not require water or air: the fields generate each other and so can move through a vacuum (such as outer space).

This was such a disturbing idea to nineteenth-century scientists that they actually made up a substance to fill all of space—one for which there was not a single shred of evidence—just so light waves could have something to travel through: they called it the aether.

Explain what the ionosphere is and how it interacts with some radio waves.

FM and TV waves are not absorbed and can travel easily through our atmosphere.

AM radio waves are absorbed or reflected by Earth's ionosphere

(the ionosphere is a layer of charged particles at the top of our atmosphere, produced by interactions with sunlight and charged particles that are ejected from the Sun).

Which is more dangerous to living things, gamma rays or X-rays? Explain.

Gamma rays; Because gamma rays carry a lot of energy, they can be dangerous for living tissues.

Explain why we have to observe stars and other astronomical objects from above Earth's atmosphere in order to fully learn about their properties.

It is important to observe the Sun and other astronomical objects in wavelengths other than the visible band of the spectrum.

Due to Earth's atmosphere absorbs much of the ultraviolet light coming from space

Explain why hotter objects tend to radiate more energetic photons compared to cooler objects.

Higher-energy photons correspond to higher-frequency waves (which have a shorter wavelength); lower-energy photons are waves of lower frequency.

when electrons go from lower levels to higher ones, they must absorb a photon of just the right energy, and when they go from higher levels to lower ones, they give off a photon of just the right energy.

Explain how we can deduce the temperature of a star by determining its color.

The higher the temperature, the shorter the wavelength at which the peak amount of energy is radiated.

This is because in any solid or denser gas, some molecules or atoms vibrate or move between collisions slower than average and some move faster than average.

So when we look at the electromagnetic waves emitted, we find a broad range, or spectrum, of energies and wavelengths.

More energy is emitted at the average vibration or motion rate (the highest part of each curve), but if we have a large number of atoms or molecules, some energy will be detected at each wavelength.

Explain what dispersion is and how astronomers use this phenomenon to study a star's light.

The separation of different wavelengths of white light through refraction of different amounts

Explain why glass prisms disperse light.

When white light passes through a prism, it is dispersed and forms a continuous spectrum of all the colors.

Explain what Joseph Fraunhofer discovered about stellar spectra.

Joseph Fraunhofer, discovered that there are more than 600 dark lines, which led scientists to rule out the boundary hypothesis

Explain how we use spectral absorption and emission lines to determine the composition of a gas.

Each particular gas can absorb or emit only certain wavelengths of the light peculiar to that gas. It's the precise pattern of wavelengths that makes the signature of each element unique.

Explain the results of Rutherford's gold foil experiment and how they changed our model of the atom.

When Rutherford allowed α particles from a radioactive source to strike a target of gold foil, he found that, although most of them went straight through, some rebounded back in the direction from which they came.

(From this experiment, he concluded that the atom must be constructed like a miniature solar system, with the positive charge concentrated in the nucleus and the negative charge orbiting in the large volume around the nucleus.

Is it possible for two different atoms of carbon to have different numbers of neutrons in their nuclei?

Yes, Atoms with the same number of proton but different numbers of neutrons are defined as Isotopes and there elements remain the same. Think of isotopes as siblings in the same element "family"—closely related but with different characteristics and behaviors.

What are the three isotopes of hydrogen, and how do they differ?

H1 (Hydrogen 0Neutrons)

H2 (deuterium, 1Neutrons)

H3 (tritium, 2Neutrons)

Explain how electrons use light energy to move among energy levels within an atom.

An atom can absorb energy(photons), which raises it to a higher energy level, this causes an electron's movement to a larger orbit and is called excitation.

Explain why astronomers use the term "blueshifted" for objects moving toward us and "redshifted" for objects moving away from us.

As wavelength gets shorter, they shift toward the blue end of the spectrum: astronomers call this a blueshift.

When the wavelength gets longer, we call the change in colors a redshift.

If spectral line wavelengths are changing for objects based on the radial velocities of those objects, how can we deduce which type of atom is responsible for a particular absorption or emission line?

It is the precise wavelength (or color) that tells astronomers which lines belong to which element.