Quantum Physics Questions

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Very Short Answers Questions [1 Mark Questions]

Ques. According to quantum mechanics, the photoelectric equation is given by

1. K_max = hf - ϕ
2. K_max = hf + ϕ
3. K_max = hf x ϕ
4. K_max = hf/ϕ

Ans. The correct answer is a. K_max = hf - ϕ

Explanation: The Einstein’s photoelectric equation is given by

K_max = hf - ϕ

Where K_max is the maximum kinetic energy, ϕ is the work function, and hf is the energy of a photon.

Ques. Which field considers the dual behavior of matter?

1. Optics
2. Quantum physics
3. Classical physics
4. None of the above

Ans. The correct answer is b. Quantum physics

Explanation: Quantum physics is a basic theory of physics that describes the physical features of nature at the atomic and subatomic particle scales.

Ques. The momentum of a particle is equal to the product of _____ and _____.

1. Mass, weight
2. Mass, acceleration
3. Mass, force
4. Mass, velocity

Ans. The correct answer is d. Mass, velocity

Explanation: Momentum is a fundamental concept in physics that quantifies an object's motion. It is calculated as the product of an object's mass and velocity.

Ques. Heisenberg’s uncertainty principle is also known as

1. Unpredictable principle
2. Uncertainty principle
3. Indeterminacy principle
4. Both Uncertainty and Indeterminacy principle

Ans. The correct answer is d. Both Uncertainty and Indeterminacy principle

Explanation: The uncertainty principle, also known as the Heisenberg uncertainty principle or the indeterminacy principle, is a statement made by the German physicist Werner Heisenberg in 1927 that the position and velocity of an object cannot be measured exactly at the same time, even in theory.

Ques. Who coined the term quantum mechanics?

Ans. The term "quantum mechanics" was coined by a group of physicists at the University of Göttingen in the early 1920s, including Max Born, Werner Heisenberg, and Wolfgang Pauli.

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Short Answers Questions [2 Marks Questions]

Ques. What is Quantum Physics?

Ans. Quantum Physics is defined as the study of physics on a microscopic level, such as how atoms or electrons move. It is a branch of modern physics that explains how modern civilization works and how all scientific study is conducted. Quantum physics explains the nature of the particles that make up matter, as well as the forces that keep them together or cause them to interact.

Ques. What is Physics?

Ans. Physics is a natural science that studies matter, its fundamental constituents, motion and behavior in space and time, and the associated phenomena of energy and force.

Ques. What is meant by classical physics?

Ans. Classical physics refers to scientific concepts that predate newer, more comprehensive, or widely applicable theories. Throughout classical physics, energy and matter were considered separate entities.

Ques. What is Quantum Theory?

Ans. Quantum Theory is the theoretical study of matter and its characteristics in terms of atoms, protons, neutrons, electrons, and so on. It defines a number of concepts and theories for the study of quantum mechanics and its applications. 

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Long Answers Questions [3 Marks Questions]

Ques. What are the three forces in quantum physics?

Ans. The three forces in quantum physics are

• Electromagnetic force: The electromagnetic force is one of nature's four fundamental forces. It is the dominant force in atom-molecule interactions.
• Strong nuclear force: The strong interaction, also known as the strong force or strong nuclear force in quantum physics, is a fundamental interaction that restricts quarks into proton, neutron, and other hadron particles.
• Weak nuclear force: The weak nuclear force is the mechanism of interaction between subatomic particles that causes the radioactive decay of atoms.

Ques. What are the uses of Quantum Physics?

Ans. The following are the uses of Quantum physics

• It is a branch of modern physics that explains how modern civilization works and how all research is conducted.
• Quantum physics describes how biological and chemical processes function.
• It also enlightens us on how atoms and their constituents, such as the electron, proton, and neutron, behave and interact with one another.
• Quantum Physics provides a thorough explanation of the forces involved in action, reaction, or phenomenon.

Ques. Why do we need Quantum physics?

Ans. Quantum physics leads to some extremely strange conclusions about the physical world. 

• Many of the equations studied in classical physics that describe how objects move at daily sizes and speeds no longer appear to be applicable at the scale of atoms and electrons. 
• This is due to the fact that in quantum physics, objects exist in probability, which means they have a certain chance of being at point A, another chance of being at point B, and so on, as opposed to classical mechanics, where objects exist in a given location at a certain moment.

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Very Long Answers Questions [5 Marks Questions]

Ques. What is Heisenberg’s Uncertainty Principle?

Ans. According to Heisenberg's uncertainty principle, it is impossible to accurately determine both the position and velocity of particles that have both particle and wave properties. 

• The uncertainty principle is named after German scientist Werner Heisenberg, who introduced it in 1927. 
• This idea was developed by Heisenberg while attempting to provide an intuitive model of quantum physics. 
• He observed that there were several fundamental characteristics that limited our activities when it came to knowing certain amounts. 
• This principle simply indicates that simultaneous measurement of position and velocity or momentum of small matter waves will have an error such that the product of the error in position and momentum measurement is equal to or greater than an integral multiple of a constant.

Ques. An electron has kinetic energy equal to 100 eV. Calculate

1. Momentum
2. Speed
3. The de-Broglie wavelength of the electron

Ans. Given that the kinetic energy of the electron is 100 eV

We know, 1 eV = 1.6 x 10^-19 J, therefore

K.E = 100 eV = 100 x 1.6 x 10^-19 = 1.6 x 10^-17 J

• Kinetic energy is given by

K.E = 1/2 mv²

⇒ 1/2 mv² = 1.6 x 10^-17

⇒ mv² = 3.2 x 10^-17

Multiplying both sides by the mass of the electron (m), then

⇒ m²v² = 3.2 x 10^-17 x m

But mv = p (momentum of the electron) and m = 9.1 x 10^-31 kg

⇒ p² = 3.2 x 10^-17 x 9.1 x 10^-31

⇒ Momentum, p = 5.40 x 10^-24 kg m/s

• The speed of the electron is given by

v = p/m

⇒ v = (5.40 x 10^-24)/(9.1 x 10^-31) = 5.93 x 10⁶ m/s

• de-Broglie wavelength is given by

λ = h/p 

⇒ λ = (6.625 x 10^-34)/(5.40 x 10^-24) = 1.23 Å

Ques. Write a short note on the Dual nature of the Particle de-Broglie Hypothesis.

Ans. Dual Nature of Particle de-Broglie Hypothesis: 

• Louis de Broglie proposed in 1924 that matter exhibits dual behavior, i.e., particle and wave nature. This means it has momentum as well as a wavelength. 
• The wavelength associated with a particle of mass ′ m ′ traveling with a velocity ′ v ′, according to de Broglie, is given by the equation:

λ = h/mv

where h = Planck's constant

• This equation applies to all material objects, however, it is only relevant to microscope particles. 

Planck's theory states that

E = hf = hc/λ

 Where h is Planck's constant and f is the frequency.

According to Einstein's equation, E = mc²

From the above two equations, we get 

λ = h/mc 

The above equation is the de Broglie equation. 

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