# Chapter 31: Light Quanta

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• 1.

### In the equation E = hf, the f stands for

• A.

Wave frequency as defined for sound, radio, and light waves.

• B.

The smaller wavelengths of visible light.

• C.

Frequency characteristic of quantum phenomena.

• D.

None of these

A. Wave frequency as defined for sound, radio, and light waves.
Explanation
The equation E = hf represents the relationship between energy (E) and frequency (f) in physics. In this equation, f stands for wave frequency, which is a measure of how many waves pass a given point in a certain amount of time. This frequency is applicable to sound waves, radio waves, and light waves, as they all exhibit wave-like properties. Therefore, the correct answer is "wave frequency as defined for sound, radio, and light waves."

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• 2.

### The ratio of the energy of a photon to its frequency is

• A.

Pi.

• B.

Planck's constant.

• C.

The photon's speed.

• D.

The photon's wavelength.

• E.

Not known.

B. Planck's constant.
Explanation
The correct answer is Planck's constant. This is because according to the equation E = hf, where E is the energy of a photon, h is Planck's constant, and f is the frequency of the photon. This equation shows that the energy of a photon is directly proportional to its frequency, and Planck's constant is the proportionality constant between the two. Therefore, the ratio of the energy of a photon to its frequency is Planck's constant.

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• 3.

### Which has less energy per photon?

• A.

Red light

• B.

Blue light

• C.

Both have the same energy.

A. Red light
Explanation
Red light has less energy per photon compared to blue light. This is because the energy of a photon is directly proportional to its frequency, and blue light has a higher frequency than red light. Therefore, blue light photons have more energy than red light photons.

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• 4.

### Which has more energy per photon?

• A.

Red light

• B.

Blue light

• C.

Both have the same energy.

B. Blue light
Explanation
Blue light has more energy per photon compared to red light. This is because 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. Therefore, blue light has more energy per photon than red light.

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• 5.

### Which of the following photons has the greatest energy?

• A.

Infrared

• B.

Red light

• C.

Green light

• D.

Blue light

• E.

Ultraviolet

E. Ultraviolet
Explanation
Ultraviolet photons have the greatest energy among the given options. The energy of a photon is directly proportional to its frequency, and ultraviolet light has a higher frequency compared to infrared, red, green, and blue light. This higher frequency results in greater energy per photon.

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• 6.

### The photoelectric effect best demonstrates the

• A.

Wave nature of light.

• B.

Particle nature of light.

• C.

Both of these

• D.

None of these

B. Particle nature of light.
Explanation
The photoelectric effect refers to the phenomenon where electrons are emitted from a material when it is exposed to light. This effect can only be explained by considering light as a stream of particles, known as photons, rather than as a wave. The energy of each photon is directly proportional to its frequency, and when a photon interacts with an electron in the material, it transfers its energy, causing the electron to be ejected. This behavior of light as discrete particles supports the particle nature of light.

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• 7.

### In the photoelectric effect, the brighter the illuminating light on a photosensitive surface, the greater the

• A.

Number of ejected electrons.

• B.

Velocity of ejected electrons.

• C.

Both of these

• D.

Neither of these

A. Number of ejected electrons.
Explanation
The photoelectric effect refers to the phenomenon where electrons are emitted from a photosensitive surface when it is exposed to light. The intensity of the incident light determines the number of electrons that are ejected. This is because the energy of the incident photons determines the energy of the ejected electrons. Higher intensity light means more photons, which in turn means more energy available to eject electrons. Therefore, the brighter the illuminating light, the greater the number of ejected electrons.

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• 8.

### In the photoelectric effect, the greater the frequency of the illuminating light, the greater the

• A.

Number of ejected electrons.

• B.

Maximum velocity of ejected electrons.

• C.

Both of these

• D.

Neither of these

B. Maximum velocity of ejected electrons.
Explanation
The photoelectric effect is the phenomenon where electrons are emitted from a material when it is exposed to light. The intensity of the light determines the number of electrons ejected, while the frequency of the light determines the maximum velocity of the ejected electrons. This is because the energy of a photon is directly proportional to its frequency, and the maximum kinetic energy of the ejected electrons is equal to the energy of the incident photons minus the work function of the material. Therefore, the greater the frequency of the illuminating light, the greater the maximum velocity of the ejected electrons.

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• 9.

### A lump of energy associated with light is called a

• A.

Quantum.

• B.

Photon.

• C.

Both of these

• D.

Neither of these

C. Both of these
Explanation
Both quantum and photon are correct answers because they both refer to a lump of energy associated with light. Quantum is a term used in quantum physics to describe the discrete packets of energy that light can be divided into, while photon specifically refers to a particle of light that carries this energy. Therefore, both terms accurately describe the concept of a lump of energy associated with light.

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• 10.

### A quantum of light is called a(n)

• A.

Proton.

• B.

Neutron.

• C.

Electron.

• D.

Notron.

• E.

None of these

E. None of these
Explanation
A quantum of light is called a photon. Protons, neutrons, and electrons are subatomic particles, not quanta of light. Therefore, the correct answer is "none of these."

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• 11.

### The ratio of a photon's energy to its frequency is

• A.

Its speed.

• B.

Its wavelength.

• C.

Its amplitude.

• D.

Planck's constant.

• E.

None of these

D. Planck's constant.
Explanation
The ratio of a photon's energy to its frequency is Planck's constant. This is known as the Planck-Einstein relation, which states that the energy of a photon is directly proportional to its frequency, with Planck's constant acting as the proportionality constant. This relation is a fundamental concept in quantum mechanics and helps explain the particle-like behavior of light. The speed, wavelength, and amplitude of a photon are not directly related to its energy or frequency.

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• 12.

### Light behaves primarily as a wave when it

• A.

Travels from one place to another.

• B.

Interacts with matter.

A. Travels from one place to another.
Explanation
Light behaves primarily as a wave when it travels from one place to another because it exhibits characteristics of a wave, such as interference, diffraction, and polarization. When light moves through different mediums or travels through space, it undergoes these wave-like behaviors, which can be explained by the wave nature of light. On the other hand, when light interacts with matter, it can also exhibit particle-like behaviors, such as absorption and emission of discrete packets of energy called photons. However, the primary behavior of light as it travels from one place to another is wave-like.

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• 13.

### Light behaves primarily as a particle when it

• A.

Travels from one place to another.

• B.

Interacts with matter.

B. Interacts with matter.
Explanation
When light interacts with matter, it exhibits particle-like behavior. This is known as the particle nature of light or the photon theory. When light interacts with matter, it can be absorbed, reflected, or refracted, which indicates its particle-like behavior. This behavior is explained by the concept of photons, which are discrete packets of energy that make up light. Therefore, the correct answer is "interacts with matter."

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• 14.

### Which experiment best demonstrates the particle-like nature of light?

• A.

Photoelectric effect

• B.

Double-slit experiment

• C.

Neither

A. Photoelectric effect
Explanation
The photoelectric effect best demonstrates the particle-like nature of light. This experiment involves shining light on a metal surface and observing the emission of electrons. The intensity of the light determines the number of electrons emitted, while the frequency of the light determines their energy. This phenomenon cannot be explained by wave theory alone, but it can be understood by considering light as a stream of particles called photons. Therefore, the photoelectric effect provides evidence for the particle-like behavior of light.

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• 15.

### In the double-slit experiment with electrons, the electrons arrive at the screen in a

• A.

Particle-like way with a pattern that is particle-like.

• B.

Particle-like way with a pattern that is wave-like.

• C.

Wave-like way with a pattern that is particle-like.

• D.

Wave-like way with a pattern that is wave-like.

B. Particle-like way with a pattern that is wave-like.
Explanation
In the double-slit experiment with electrons, the electrons exhibit a particle-like behavior by arriving at the screen in a localized manner. However, the pattern that is formed on the screen is wave-like in nature, characterized by interference patterns. This phenomenon suggests that electrons have both particle and wave properties, as they can exhibit particle-like behavior while also displaying wave-like interference patterns.

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• 16.

### Quantum uncertainties are most predominant for simultaneously measuring the speed and location of

• A.

A baseball.

• B.

A spitball.

• C.

An electron.

C. An electron.
Explanation
Quantum uncertainties refer to the inherent unpredictability in the behavior of particles at the quantum level. These uncertainties are most prominent when measuring both the speed and location of a particle simultaneously. While it is possible to accurately measure the speed and location of macroscopic objects like a baseball or a spitball, the same cannot be said for subatomic particles like electrons. Due to their wave-particle duality and the Heisenberg uncertainty principle, it is impossible to precisely determine both the speed and location of an electron at the same time. Therefore, the correct answer is an electron.

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• 17.

### The uncertainty principle applies not only to momentum and position, but also to energy and time. This statement is

• A.

True.

• B.

False.

A. True.
Explanation
The uncertainty principle, proposed by Werner Heisenberg, states that it is impossible to simultaneously measure certain pairs of physical properties, such as momentum and position, with absolute precision. This principle also applies to energy and time, meaning that the more accurately one tries to measure the energy of a particle, the less precisely one can determine its time of occurrence. Therefore, the given statement is true, as the uncertainty principle does apply to both momentum and position, as well as energy and time.

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• 18.

### According to the uncertainty principle, the more we know about a particle's momentum, the less we know about its

• A.

Kinetic energy.

• B.

Mass.

• C.

Speed.

• D.

Location.

• E.

None of these

D. Location.
Explanation
According to the uncertainty principle, there is a fundamental limit to how precisely we can know both the position and momentum of a particle at the same time. This means that the more accurately we determine the momentum of a particle, the less accurately we can determine its position. Therefore, if we know more about a particle's momentum, it implies that we have less knowledge about its location.

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• 19.

### According to quantum physics, looking at a star through a telescope

• A.

Affects the processes occurring in the star.

• B.

Has no effect on the processes occurring in the star.

B. Has no effect on the processes occurring in the star.
Explanation
According to quantum physics, the act of observing or looking at a star through a telescope does not have any effect on the processes occurring in the star. This is because the act of observation itself does not cause any physical interaction or influence on the star's processes. Quantum physics suggests that the behavior and properties of particles and systems are determined by various factors, but the mere act of observation does not alter these processes.

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• 20.

### In the relationship E = hf for a photon emitted from an atom, the symbol E is used to represent the energy

• A.

Of the emitted photon.

• B.

Difference between atomic energy states producing the photon.

• C.

Both of these

• D.

Neither of these

C. Both of these
Explanation
The symbol E in the relationship E = hf represents the energy of the emitted photon. This means that E represents the energy of the photon itself. Additionally, E can also represent the difference between atomic energy states that produce the photon. Therefore, the correct answer is both of these.

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• 21.

### Two beams of light, a red beam and a blue beam, have the same energy. The beam with the greater number of photons is the

• A.

Red beam.

• B.

Blue beam.

• C.

Both the same

A. Red beam.
Explanation
The red beam has a greater number of photons because red light has a longer wavelength compared to blue light. As energy is inversely proportional to wavelength, red light has lower energy per photon. Therefore, to have the same total energy as the blue beam, the red beam must have a greater number of photons.

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• 22.

### A photosensitive surface is illuminated with both blue and violet light. The light that will cause the most electrons to be ejected is the

• A.

Blue light.

• B.

Violet light.

• C.

Both eject the same number.

• D.

Not enough information given

D. Not enough information given
Explanation
The question states that a photosensitive surface is illuminated with both blue and violet light, but it does not provide any information about the properties of the surface or how it responds to different wavelengths of light. Therefore, it is not possible to determine which light will cause the most electrons to be ejected.

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• 23.

### To study the energy of photoelectrons we measure

• A.

The potential difference required to stop them.

• B.

The distance they travel in a given time.

• C.

The time they take to go a given distance.

• D.

Their temperature.

A. The potential difference required to stop them.
Explanation
The correct answer is "the potential difference required to stop them." This is because the energy of photoelectrons can be determined by measuring the potential difference needed to prevent them from moving. When a potential difference is applied, the photoelectrons can gain or lose energy depending on the direction of the electric field. By adjusting the potential difference, the energy of the photoelectrons can be precisely controlled and measured. Therefore, this method allows for the study of the energy of photoelectrons.

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• 24.

### Which of the following is not quantized?

• A.

Energy

• B.

• C.

Number of people in a room

• D.

Electric charge

• E.

All are quantized.

E. All are quantized.
Explanation
All the options given in the question are examples of quantized quantities. Quantization refers to the idea that certain physical properties can only exist in discrete, specific values rather than continuous values. In the case of energy, radiation, number of people in a room, and electric charge, all of these quantities can only exist in specific quantized values. Therefore, the correct answer is that all of the options are quantized.

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• 25.

### Two photons have the same wavelength. They also have the same

• A.

Frequency.

• B.

Energy.

• C.

Both of these

• D.

Neither of these

C. Both of these
Explanation
Two photons with the same wavelength have the same frequency and energy. This is because wavelength and frequency are inversely proportional, meaning that as the wavelength increases, the frequency decreases, and vice versa. Since the photons have the same wavelength, their frequencies must also be the same. Additionally, the energy of a photon is directly proportional to its frequency, according to the equation E = hf, where E is energy, h is Planck's constant, and f is frequency. Therefore, if the photons have the same frequency, they must also have the same energy.

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• 26.

### When a clean surface of potassium metal is exposed to blue light, electrons are emitted. If the intensity of the blue light is increased, which of the following will also increase?

• A.

The number of electrons ejected per second

• B.

The maximum kinetic energy of the ejected electrons

• C.

The threshold frequency of the ejected electrons

• D.

The time lag between the absorption of blue light and the start of emission of the electrons

• E.

None of these

A. The number of electrons ejected per second
Explanation
When the intensity of the blue light is increased, more photons are incident on the potassium surface. This leads to an increase in the number of electrons being excited and ejected from the surface per unit time. Therefore, the number of electrons ejected per second will increase. The maximum kinetic energy of the ejected electrons and the threshold frequency of the ejected electrons will remain the same, as these properties are determined by the material and not the intensity of the light. The time lag between the absorption of blue light and the start of emission of electrons will also remain the same, as it is determined by the time it takes for the electrons to be excited and ejected from the surface.

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• 27.

### An electron and a baseball move at the same speed. Which has the longer wavelength?

• A.

The electron

• B.

The baseball

• C.

Both have the same wavelength.

A. The electron
Explanation
The electron has a longer wavelength compared to the baseball. This is because the wavelength of a particle is inversely proportional to its momentum. Since the electron has a much smaller mass compared to the baseball, it will have a larger momentum for the same speed. Therefore, the electron will have a longer wavelength.

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• 28.

### If a proton and an electron have identical momenta, the longer wavelength belongs to the

• A.

Proton.

• B.

Electron.

• C.

Both the same

C. Both the same
Explanation
The wavelength of a particle is inversely proportional to its momentum. Since the proton and electron have identical momenta, their wavelengths will also be identical. Therefore, the longer wavelength does not belong to either the proton or the electron, but rather, it is the same for both particles.

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• 29.

### A bullet and a proton have the same momentum. Which has the longer wavelength?

• A.

The bullet

• B.

The proton

• C.

Both have the same wavelength.

C. Both have the same wavelength.
Explanation
The wavelength of a particle is inversely proportional to its momentum. Since the bullet and the proton have the same momentum, they will also have the same wavelength.

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• 30.

### An electron and a proton are traveling at the same speed. Which has the longer wavelength?

• A.

The electron

• B.

The proton

• C.

Both have the same wavelength.

A. The electron
Explanation
The electron has a longer wavelength compared to the proton. This is because wavelength is inversely proportional to the mass of the particle. Since the electron has a much smaller mass than the proton, it will have a longer wavelength when traveling at the same speed.

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• 31.

### According to the uncertainty principle, the more we know about a particle's position, the less we know about its

• A.

Speed.

• B.

Momentum.

• C.

Kinetic energy.

• D.

All of these

• E.

None of these

D. All of these
Explanation
The uncertainty principle states that there is a fundamental limit to the precision with which certain pairs of physical properties, such as position and momentum, can be known simultaneously. This means that the more accurately we know the position of a particle, the less accurately we can know its speed, momentum, and kinetic energy. Therefore, the correct answer is all of these.

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• 32.

• A.

Its position.

• B.

The time it has that energy.

• C.

Both of these

• D.

Neither of these

C. Both of these
Explanation
The uncertainty principle in quantum mechanics states that the more precisely one knows the energy of a particle, the less precisely one can know its position and vice versa. This means that if one has more information about the energy of an electron, it implies that there is less certainty about its position and the time it has that energy. Therefore, the correct answer is both of these.

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• 33.

### According to quantum physics, measuring the velocity of a tiny particle with an electromagnet

• A.

Affects the velocity of the particle.

• B.

Has no effect on the velocity of the particle.

A. Affects the velocity of the particle.
Explanation
According to the principles of quantum physics, the act of measuring the velocity of a tiny particle with an electromagnet affects the velocity of the particle. This is due to the inherent nature of quantum mechanics, where the act of observation or measurement influences the properties of the observed system. In this case, the measurement process itself perturbs the particle's velocity, leading to a change in its behavior.

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• 34.

### According to quantum physics, measuring the temperature of lava from a distant volcano by photographing its color with a telescopic camera

• A.

Affects the temperature of the lava.

• B.

Has no effect on the temperature of the lava.

B. Has no effect on the temperature of the lava.
Explanation
According to quantum physics, the act of measuring the temperature of lava by photographing its color with a telescopic camera does not have any effect on the actual temperature of the lava. In quantum physics, the act of observation or measurement does not alter the properties or behavior of the observed object. Therefore, the temperature of the lava remains unaffected by the process of measuring it with a telescopic camera.

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• 35.

### A radiation detector measures the radioactivity of a piece of radium by catching and counting alpha particles it emits. According to quantum physics, making this measurement affects the

• A.

• B.

Alpha particles that are caught.

• C.

Both of these

• D.

Neither of these

B. Alpha particles that are caught.
Explanation
According to quantum physics, making a measurement affects the particles being measured. In the case of a radiation detector measuring the radioactivity of radium, the act of catching and counting alpha particles emitted by the radium affects the radiation rate of the radium itself. This is because the act of measurement disturbs the system being measured, causing a change in its behavior. Therefore, the correct answer is "alpha particles that are caught."

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• 36.

### In the photoelectric effect, electrons ejected from bound states in the photosensitive material have

• A.

Less kinetic energy than the absorbed photon's energy.

• B.

More kinetic energy than the absorbed photon's energy.

• C.

Kinetic energy equal to the absorbed photon's energy.

A. Less kinetic energy than the absorbed photon's energy.
Explanation
In the photoelectric effect, when electrons are ejected from bound states in the photosensitive material, they have less kinetic energy than the absorbed photon's energy. This is because some of the absorbed energy is used to overcome the binding energy of the electron in the material. Therefore, the remaining energy is converted into the kinetic energy of the ejected electron, resulting in it having less kinetic energy than the absorbed photon's energy.

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• 37.

### In the photoelectric effect, doubling the frequency of incident light will cause the maximum energy of ejected electrons to

• A.

Double.

• B.

Increase, but not double.

• C.

More than double.

• D.

Decrease.

C. More than double.
Explanation
When the frequency of incident light is doubled in the photoelectric effect, the energy of the ejected electrons increases proportionally to the frequency. According to the equation E = hf, where E is the energy, h is Planck's constant, and f is the frequency, doubling the frequency will result in the energy of the ejected electrons also doubling. Therefore, the correct answer is "increase, but not double."

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• 38.

### Which of the following has the longer wavelength?

• A.

A low-energy electron

• B.

A high-energy electron

• C.

Both have the same wavelength.

A. A low-energy electron
Explanation
A low-energy electron has a longer wavelength compared to a high-energy electron. This is because wavelength and energy are inversely proportional. As the energy of an electron increases, its wavelength decreases. Therefore, a low-energy electron has a longer wavelength than a high-energy electron.

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• 39.

### Which of the following are conserved when a photon collides with an electron?

• A.

Momentum, energy, and velocity

• B.

Momentum and energy

• C.

Momentum and velocity

• D.

Energy and velocity

• E.

None of the above choices are correct.

B. Momentum and energy
Explanation
When a photon collides with an electron, momentum and energy are conserved. Momentum is conserved because the total momentum before the collision (which is zero since the electron is at rest) must be equal to the total momentum after the collision. Energy is conserved because the total energy before the collision (which is equal to the energy of the photon) must be equal to the total energy after the collision. Velocity is not conserved because the collision can cause the electron to change its velocity. Therefore, the correct answer is momentum and energy.

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• 40.

### Which of the following forms an interference pattern when directed toward two suitably spaced slits?

• A.

Light

• B.

Sound

• C.

Electrons

• D.

All of these

• E.

None of these

D. All of these
Explanation
All of these options (light, sound, and electrons) can form an interference pattern when directed toward two suitably spaced slits. This is because interference patterns occur when waves interact with each other and either reinforce or cancel each other out. Light waves can form interference patterns, as seen in the famous double-slit experiment. Similarly, sound waves can form interference patterns, such as when they pass through two small openings. Even electrons, which have wave-particle duality, can exhibit interference patterns when directed through a double-slit setup. Therefore, all of these options are correct.

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• 41.

### According to the correspondence principle, a new theory is valid if it

• A.

Overlaps and agrees where the old theory works.

• B.

Accounts for confirmed results from the old theory.

• C.

Predicts the same correct results as the old theory.

• D.

All of these

• E.

None of these

D. All of these
Explanation
The correct answer is "all of these". According to the correspondence principle, a new theory is considered valid if it overlaps and agrees with the old theory where it has been successful, accounts for confirmed results from the old theory, and predicts the same correct results. In other words, a new theory should encompass and build upon the successes of the old theory while also providing new insights and predictions.

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• 42.

### The phenomenon that can be explained only in terms of the particle model of light is

• A.

Reflection.

• B.

Refraction.

• C.

Photoelectric effect.

• D.

Diffraction.

• E.

None of the above choices are correct.

C. Photoelectric effect.
Explanation
The photoelectric effect is a phenomenon that can only be explained using the particle model of light. This effect occurs when light, which is composed of particles called photons, strikes a material and causes the ejection of electrons. The energy of the photons determines whether or not electrons are ejected, and this behavior is best explained by treating light as particles rather than waves. Reflection, refraction, and diffraction can all be explained using the wave model of light, so they are not the correct answer.

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