# IFS (Forests Services) Physics (Mains): Questions 24 - 30 of 34

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## Question number: 24

» Molecular Physics » Molecular Hydrogen in Astronomy Fluorescence and Phosphorescence

Appeared in Year: 2011

### Describe in Detail

What is the mechanism of emission of light on fluorescent lamps and in painted signboards?

### Explanation

A fluorescent lamp is containing liquid mercury and argon (or xenon) or krypton in a glass tube. This glass tube is coated with a fluorescent, which is made of varying blends of metallic and phosphor powder.

At the end of the tube, there is a cathode ma

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## Question number: 25

» Physical Optics » Polarisation and Modern Optics » Ruby and He-Ne Lasers

Appeared in Year: 2013

### Describe in Detail

Explain the lasing action of laser using energy level diagram and describe the operation of laser experimental setup. (Section A)

### Explanation

The light is produced in He – Ne laser by atomic transitions in the Neon atom. The Helium acts as a buffer gas in it. That means Helium doesn’t directly produce laser light, it only helps the atom of the Neon gas to produce lasing in as manner.

Helium absorbed some energy, when energy applied to the He – Ne gas mixture, and it achieve an excited sta

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## Question number: 26

» Quantum Mechanics I » Particle in a Finite Well, Linear, Harmonic Oscillator, Reflection

Appeared in Year: 2011

### Describe in Detail

Solve the Schrodinger equation for a potential step function given by,

and calculate the reflection and transmission coefficients. Show that for there is a finite probability of finding the particle in a classically forbidden region.

### Explanation

Consider . The time independent Schrodinger equation in one dimension is given as,

And according to question, the potential step function is given as,

Let the region of negative is denoted by and region of positive is denoted by . Also corresponding wave functions

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## Question number: 27

» Quantum Mechanics II & Atomic Physics » Quantum Mechanics II » The Spin Half Problem and Properties of Pauli Spin Matrices

Appeared in Year: 2011

### Describe in Detail

What are Pauli spin matrices?

Show that:

Where, are Pauli spin matrices and and are vector operators which commute with , but do not necessarily commute with each other?

### Explanation

Pauli spin matrices or Pauli matrices are a set of matrices, which are complex, Hermitian and unitary matrices. Pauli spin matrices defined as,

The Pauli vector is defined by,

From question another vector operators are and are given.

Now, mapping mechanism from a Pauli matrix basis and a

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## Question number: 28

» Molecular Physics » Elementary Theory of Rotational, Vibrational and Electronic Spectra of Diatomic Molecules

Appeared in Year: 2011

### Describe in Detail

Give the elementary theory of NMR. Explain the two different relaxation processes. (Paper – II)

### Explanation

In Nuclear Magnetic Resonance (NMR), the frequency of processing nucleus is equal to the frequency of rotating magnetic field. Here it is important to notice that in NMR we are not performing experiments on the electron, it all about the nuclei of the nucleus.

The principle of NMR is dependent on the spins of atomic nuclei. Consider, the subatomic p

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## Question number: 29

» Quantum Mechanics I » Schroedinger Equation and Expectation Values

Appeared in Year: 2011

### Describe in Detail

For a quantum mechanical system prove that all energy eigen – values are real and if , then the corresponding eigen functions are orthogonal.

### Explanation

The eigenvalue equation, of the sets of energies and wave functions obtained by any quantum mechanics problems is given as,

For another value of the quantum number, we can write

Multiply equation (1) by and the complex conjugate of equation (2) by . Then subtract the two expressions and integrate over .

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## Question number: 30

» Particle Physics & Solid State Physics » Solid State Physics » Band Theory of Solids-Conductors

Appeared in Year: 2011

### Describe in Detail

How are the band structures of insulators and semiconductors similar? How are they different?

### Explanation

- There is only one similarity in band structures of insulators and semiconductors. That is band gab between valence band and conduction band. And in case of conductor, there is no such band gap between valence and conduction bands.

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