Chapter 30: Light Emission

The radiation curve for a "blue hot" object peaks in the ultraviolet region. This is because the temperature of a blue hot object is very high, causing it to emit shorter wavelength radiation. As temperature increases, the peak of the radiation curve shifts towards shorter wavelengths, eventually reaching the ultraviolet region.

When an atom emits a certain frequency of light, it means that the electrons in the atom are transitioning from higher energy levels to lower energy levels. This emission occurs when the electrons release energy in the form of photons. On the other hand, when an atom absorbs a certain frequency of light, it means that the electrons are transitioning from lower energy levels to higher energy levels by absorbing energy from photons. Therefore, an atom that emits a certain frequency of light is more likely to absorb that same frequency, as the energy levels of the electrons in the atom are compatible with that specific frequency.

Fluorescence is a process where a substance absorbs high-frequency light and then emits lower-frequency light. This phenomenon occurs because the absorbed energy is temporarily stored by the substance and then released as light of a longer wavelength. Therefore, the correct answer is "lower-frequency light."

The highest frequency light among the options given is violet. In the electromagnetic spectrum, different colors of light are associated with different frequencies. Violet light has the highest frequency among the visible light spectrum, while red light has the lowest frequency. Therefore, violet light has a higher frequency than red, green, blue, and all the other colors mentioned in the options.

If light in a spectroscope passed through round holes instead of slits, the spectral lines would appear round. This is because the shape of the aperture through which light passes affects the shape of the resulting spectrum. Slits create narrow, elongated lines, while round holes would produce circular lines. Therefore, if round holes were used instead of slits, the spectral lines would appear round.

The energy of a photon is directly proportional to its frequency. Blue light has a higher frequency than red light, which means that each photon of blue light carries more energy compared to a photon of red light. Therefore, the energy of a photon of blue light is more than that of a photon of red light.

The explanation for the given correct answer is that atoms of neon in a glass tube can be excited repeatedly. This means that once an atom of neon is excited, it can return to its ground state and be excited again multiple times. This is possible because the energy that excites the atom can be continuously supplied, allowing the atom to undergo repeated excitation and relaxation cycles.

The light from a lit match comes from electrons. When the match is struck, the heat causes the atoms in the matchstick to become excited. As the electrons in the atoms return to their ground state, they release energy in the form of light. This process is known as electron transition. Therefore, it is the movement of electrons that produces the light from a lit match.

The radiation curve for a "red hot" object peaks in the infrared region because as an object gets hotter, it emits electromagnetic radiation. The wavelength of this radiation is inversely proportional to the temperature of the object. As the object becomes hotter, the peak wavelength of the radiation shifts towards shorter wavelengths. In the case of a "red hot" object, the peak wavelength falls in the infrared region, which is longer than visible light but shorter than radio waves. Therefore, the correct answer is the infrared region.

Electrons with greater potential energies are the ones located farther away from the atomic nucleus. Outer electrons have higher potential energies because they are further from the positively charged nucleus and experience weaker attraction. On the other hand, inner electrons are closer to the nucleus and are held more tightly due to stronger electrostatic forces. Therefore, outer electrons have greater potential energies compared to inner electrons.

A fluorescent lamp is more energy-efficient compared to an incandescent lamp. This is because fluorescent lamps use a different technology that produces light by passing an electric current through a gas, which causes the gas to emit ultraviolet light. This ultraviolet light then interacts with a phosphor coating on the inside of the lamp, producing visible light. In contrast, incandescent lamps produce light by heating a filament until it becomes white-hot, which requires a significant amount of energy. Therefore, fluorescent lamps consume less energy and are considered more energy-efficient.

Fluorescent minerals on display in museums are illuminated with ultraviolet light. When ultraviolet light shines on these minerals, it causes them to absorb the light energy and re-emit it as visible light, creating a vibrant and colorful display. Infrared light does not have the same effect on fluorescent minerals, and while some museums may use both ultraviolet and infrared light for different purposes, ultraviolet light is the primary source of illumination for these minerals.

The hottest star is blue. This is because the temperature of a star determines its color, with hotter stars emitting more blue light. The color of a star is directly related to its surface temperature, with blue stars being the hottest and red stars being the coolest. Therefore, the correct answer is blue.

The greater number of spectral lines in the light from the neon gas tube can be explained by the fact that neon gas emits light at specific wavelengths when it is excited. These wavelengths correspond to the different energy levels of the neon atoms. On the other hand, a helium-neon laser produces a single wavelength of light by stimulating the neon gas with a helium discharge. Therefore, the neon gas tube would have a greater number of spectral lines compared to the laser beam.

When minerals are illuminated with ultraviolet light, the ultraviolet photons transfer their energy to the atomic electrons in the mineral. This causes the electrons to move into higher energy states, resulting in the glow of the mineral. This explanation is supported by the fact that minerals do not glow when illuminated with other types of light, as those photons do not have enough energy to kick the electrons into higher energy states.

The dark lines in the sun's spectrum represent light that is absorbed by the sun's atmosphere. This occurs because the sun's atmosphere contains various elements and molecules that can absorb specific wavelengths of light. When light passes through the sun's atmosphere, these elements and molecules absorb certain wavelengths, resulting in dark lines in the spectrum. This phenomenon is known as absorption spectroscopy and is used to study the composition and properties of celestial objects.

The fact that the air you breathe doesn't give off much visible light suggests that most of the electrons in its atoms are in the ground state. The ground state is the lowest energy state that an electron can occupy within an atom. When electrons are in the ground state, they are not excited or in higher energy states that would cause them to emit visible light. Therefore, the lack of visible light emission indicates that the electrons in the air atoms are in their lowest energy state, which is the ground state.

Violet light carries the most energy per photon because it has the highest frequency and shortest wavelength among the given options. According to the wave-particle duality of light, the energy of a photon is directly proportional to its frequency. Therefore, since violet light has the highest frequency, it also has the highest energy per photon.

When a solid is heated, it starts to emit light as its temperature increases. This phenomenon is known as incandescence. The color of the emitted light depends on the temperature of the solid. At lower temperatures, the emitted light appears red. As the temperature increases further, the color of the emitted light shifts towards yellow, then white, and finally blue at the highest temperatures. Therefore, the first color to glow when a solid is gradually heated is red.

The Doppler effect is the correct answer because it is a phenomenon that occurs when there is a change in frequency or wavelength of a wave, such as light or sound, due to the relative motion between the source and the observer. Astronomers can use the Doppler effect to determine whether a star is approaching or receding from Earth by analyzing the shift in the star's spectral lines. If the lines are shifted towards the blue end of the spectrum, it indicates that the star is approaching, while a shift towards the red end indicates that the star is receding.

The correct answer is "electromagnetic energy." Ultraviolet light is a form of electromagnetic radiation, just like X-rays, visible light, and radio waves. Electromagnetic energy refers to the energy carried by these waves, which can travel through a vacuum and are characterized by their wavelength and frequency. Ultraviolet light falls within the electromagnetic spectrum, having a shorter wavelength and higher energy than visible light. Therefore, it is more accurate to describe ultraviolet light as a form of electromagnetic energy rather than stating that it is more energetic than X-rays or produced by crossed Polaroids.

When light from two closely spaced stars reaches the Earth's surface, it may not produce a steady interference pattern due to incoherence. Incoherence refers to the lack of a constant phase relationship between the waves emitted by the two stars. This can happen if the waves have different frequencies or if there are random phase fluctuations caused by factors such as atmospheric turbulence. The inherent instability of the atmosphere can also contribute to the lack of a steady interference pattern, but incoherence specifically refers to the lack of phase coherence between the waves. The other options, such as different radial distances or non-point like natures of the stars, do not directly affect the interference pattern.

The main visible difference between phosphorescent and fluorescent materials is an afterglow. Phosphorescent materials continue to emit light after the excitation source is removed, resulting in a prolonged glow. On the other hand, fluorescent materials only emit light while the excitation source is present. Therefore, the presence of an afterglow is the key characteristic that distinguishes phosphorescent materials from fluorescent materials.

Neon signs glow white because the energy levels in the neon atom are discrete. When an electric current is passed through the neon gas inside the sign, the electrons in the neon atoms are excited to higher energy levels. As these electrons return to their original energy levels, they emit light of specific wavelengths. In the case of neon, the emitted light is a combination of red, orange, and yellow wavelengths, which together appear white to our eyes. If the energy levels were not discrete, the emitted light would not be specific to neon, and the sign would not appear white.

A throbbing pulse of electromagnetic radiation is called a photon. A photon is a fundamental particle that represents a quantum of light or electromagnetic radiation. It carries energy and momentum and is responsible for transmitting electromagnetic force. Photons can exhibit wave-like and particle-like properties, and they travel at the speed of light. They are emitted and absorbed by charged particles during various electromagnetic interactions, such as in the form of visible light, radio waves, X-rays, or gamma rays.

Atoms can be excited by various means, including thermal agitation, electron impact, and photon impact. Thermal agitation refers to the random motion of atoms due to their temperature, which can cause them to gain energy and become excited. Electron impact occurs when high-energy electrons collide with atoms, transferring energy and causing excitation. Photon impact, or absorption of photons, can also excite atoms by transferring energy to their electrons. Therefore, all of these options can lead to the excitation of atoms.

If light in a spectroscope were passed through a star-shaped opening instead of a thin slit, the spectral lines would appear as stars. This is because the star-shaped opening would diffract the light, causing it to spread out in different directions. As a result, the spectral lines would appear as distinct points of light, resembling stars. However, the resolution would be poorer compared to when the light is passed through a thin slit, as the star-shaped opening would cause the lines to overlap and become less defined.

The correct answer is "separate from one another." When we say that energy levels in an atom are discrete, it means that they are distinct and distinct from each other. In other words, each energy level has a specific value and is not continuous or blended with other energy levels. This is a fundamental concept in quantum mechanics, where energy is quantized and can only take on certain discrete values. Therefore, the energy levels in an atom are separate and distinct from one another.

The correct answer is phosphors on the inner surface of the lamp. Fluorescent lamps work by passing an electric current through a gas-filled tube, which excites the mercury vapor inside. The excited mercury atoms then emit ultraviolet light. The inner surface of the lamp is coated with phosphors, which absorb the ultraviolet light and re-emit it as visible white light. Therefore, the phosphors on the inner surface of the lamp are responsible for the white light emitted by a fluorescent lamp.

The correct answer is "all of these" because light from a laser is monochromatic, meaning it consists of a single wavelength or color. It is also in phase, meaning the crests and troughs of the light waves align with each other. Additionally, laser light is coherent, meaning it has a consistent and constant phase relationship between the waves. Therefore, all of these statements accurately describe light from a laser.

All of these options continually emit electromagnetic radiation. Insects emit electromagnetic radiation in the form of heat and light, radio antennas emit radio waves which are a form of electromagnetic radiation, and red-hot coals emit thermal radiation which is also a form of electromagnetic radiation. Therefore, all of these options continually emit electromagnetic radiation.

The energy of the laser beam is less than the energy put into the laser because some of the energy is lost as heat or absorbed by the medium through which the laser beam passes. Additionally, a portion of the energy is used to stimulate the emission of photons in the laser cavity. Therefore, the output energy of the laser beam is typically lower than the input energy.

During the process of fluorescence, a portion of the input energy is absorbed by the material and converted into internal energy. This internal energy is then released as lower-frequency light, which is emitted by the material. The remaining energy is not emitted as higher-frequency light or used to excite other atoms or electrons to metastable states. Therefore, the correct answer is that part of the input energy becomes internal energy, and the rest is emitted as lower-frequency light.

The greater proportion of energy is immediately converted to heat rather than light in an incandescent lamp. This is because incandescent lamps work by passing an electric current through a tungsten filament, which becomes so hot that it emits visible light. However, a significant amount of the electrical energy is lost as heat, making incandescent lamps less energy-efficient compared to fluorescent lamps, where a greater proportion of energy is converted to light rather than heat.

Helium was first discovered in the sun. This is because helium is primarily produced through nuclear fusion reactions in the sun's core. These reactions convert hydrogen into helium, releasing a tremendous amount of energy in the process. Helium was later identified on Earth, including in the laboratory, but its initial discovery can be attributed to observations of the sun's spectrum, which revealed the presence of this element.

The correct answer is "they are simply images of a vertical slit." Spectral lines take the shape of vertical lines because when light passes through a narrow vertical slit, it diffracts and spreads out horizontally. This diffraction pattern appears as vertical lines on a spectrograph, representing the specific wavelengths of light emitted or absorbed by the atom.

The energy of a photon depends on its frequency. This is because the energy of a photon is directly proportional to its frequency according to the equation E = hf, where E is the energy, h is Planck's constant, and f is the frequency. The speed and amplitude of a photon do not affect its energy.

The presence of iron absorption lines in the solar spectrum suggests that iron exists in the solar atmosphere. These absorption lines are formed when the cooler gases in the outer layers of the sun absorb specific wavelengths of light emitted by the hotter inner layers. Since iron absorption lines are observed, it indicates that iron is present in the atmosphere of the sun.

An excited atom is an atom that has one or more displaced electrons. When an atom is excited, it absorbs energy and one or more electrons move to higher energy levels or even become completely detached from the atom. This displacement of electrons causes the atom to be in an excited state.

When isolated bells ring, the sound waves are able to travel freely and are not obstructed, resulting in a clear ring. Similarly, light from a gas discharge tube is produced when electrons pass through a gas, creating a clear and focused light. On the other hand, when bells are crammed in a box, the sound waves are obstructed and cannot travel freely, resulting in a muffled ring. This is analogous to the light produced by an incandescent lamp, which is diffused and not focused like the light from a gas discharge tube or a laser. Therefore, the sound from the box crammed with bells is analogous to light from an incandescent lamp.

The correct answer is about one percent. This is because classroom lasers are not very efficient in converting electrical energy into laser light. Only a small fraction of the electrical energy is actually converted into laser light, while the rest is wasted as heat. Therefore, the efficiency of classroom lasers is typically around one percent.

When an object emits light waves instead of infrared waves, it means that it is emitting waves with higher energy and shorter wavelengths. This corresponds to a higher temperature according to the principles of thermal radiation. As temperature increases, the object's atoms and molecules vibrate more vigorously, resulting in the emission of higher energy light waves. Therefore, if the object were to emit light waves instead of infrared waves, its temperature would have to be higher.

When a flashlight filament glows red instead of white, it indicates a lowness of current in the filament, a low battery strength, and a high filament temperature. The red glow suggests that the current flowing through the filament is not sufficient to heat it up to its normal operating temperature, which is why it appears red instead of white. Additionally, a low battery strength can result in a decrease in the current flowing through the filament. Lastly, a high filament temperature can also cause the filament to emit a red glow instead of white. Therefore, all of these factors can contribute to the filament glowing red.

Some light switches glow in the dark after the lights are turned off due to a phenomenon called phosphorescence. Phosphorescent materials have the ability to absorb and store energy when exposed to light, and then release that energy slowly over time, causing them to continue glowing in the dark. This time delay between excitation (when the material absorbs energy) and de-excitation (when the material releases the stored energy) is the reason behind the glow. Fluorescence, resonance, and incandescence do not accurately explain this phenomenon.

Discrete spectral lines occur when excitation takes place in a gas. When atoms or molecules in a gas are excited, they absorb energy and their electrons move to higher energy levels. As the electrons return to their original energy levels, they release the excess energy in the form of light. This emitted light consists of specific wavelengths, resulting in discrete spectral lines. In contrast, solids, liquids, and superconductors have more closely packed atoms or molecules, leading to a broader range of energy levels and a continuous spectrum rather than discrete lines. Therefore, the correct answer is gas.

The red laser beam from a helium-neon laser corresponds to a spectral line of neon. This is because helium-neon lasers use a mixture of helium and neon gases, and the red laser beam is produced when the neon gas is excited and emits light at a specific wavelength. Therefore, the red laser beam is directly associated with the spectral line of neon gas.

The correct answer is that partially absorbent material must exist between the light source and spectroscope. This is because absorption spectra occur when certain wavelengths of light are absorbed by a material, resulting in dark lines or bands in the spectrum. In order for this to happen, there must be a material that can absorb some of the light between the source and the spectroscope. This material could be a gas, liquid, or solid, but it must have the ability to absorb certain wavelengths of light.

Under very high pressure, the spectrum of a mercury vapor lamp begins to look like that from an incandescent source. This is because the high pressure causes the mercury atoms to collide with each other more frequently, resulting in a broadening of the spectral lines. As a result, the spectrum starts to resemble the continuous spectrum produced by an incandescent source, where all wavelengths of light are present.

When an electron makes a transition to a lower energy level, it releases energy in the form of light. This is because electrons in an atom exist in specific energy levels or orbitals. When an electron absorbs energy, it moves to a higher energy level. However, it is unstable at this higher level and eventually returns to its original, lower energy level. During this transition, the excess energy is emitted as light. Therefore, the correct answer is that light is emitted when an electron makes a transition to a lower energy level.

The variety of colors seen in a burning log is due to electron transitions in various atoms. When atoms absorb energy from the heat of the fire, their electrons move to higher energy levels. As the electrons return to their original positions, they release energy in the form of light. The specific energy levels and transitions determine the wavelengths of light emitted, resulting in a range of colors. Therefore, the variety of colors seen in a burning log is a result of electron transitions in various atoms.