# IFS (Forests Services) Physics (Mains): Questions 6 - 10 of 34

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## Question number: 6

» Electricity and Magnetism » Current Electricity » Self and Mutual Inductances

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Appeared in Year: 2012

Essay Question▾

### Describe in Detail

Explain the term ‘mutual inductance’ between two coils carrying current. Describe a method of determining mutual inductance between two coils of wire with relevant theory. (Paper-1) (Section-B)

### Explanation

• By changing magnetic field around turns of an inductor, an emf induced in it and this emf is also induced in the same circuit by changing in current, this effect is called Self-induction (L) .

• When a coil in which emf induced situated in the region of the same magnetic field, the induced emf is called Mutual induction. If two or more coils are magne

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## Question number: 7

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Appeared in Year: 2011

Essay Question▾

### Describe in Detail

On the basis of uncertainty principle calculate the size of Hydrogen atom.

(Paper-2) (Section - A)

### Explanation

• From a hydrogen atom, it is not possible to predict exact the position of the electron or the momentum of the electron. Every time the electron is at somewhere but it has amplitude to in different places so there is a probability of it being found in different places.
• These places cannot all be at the nucleus; we shall suppose there is a spread in p

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## Question number: 8

» Classical Mechanics » System of Particles » Generalised Coordinates and Momenta

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Appeared in Year: 2012

Essay Question▾

### Describe in Detail

Starting with Newton’s second law of motion, establish D’ Alembert’s principle and discuss its significance? (Paper-1) (Section –A)

### Explanation

• Let consider a system described by generalized coordinates . And this system undergoes a certain displacement in configuration space. If for this displacement it does not take any time and it is consistent with the constraints on the system. This kind of displacement is called virtual.

• In virtual displacement there

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## Question number: 9

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Appeared in Year: 2011

Essay Question▾

### Describe in Detail

(i) What angle do the make with the z – axis when for an electron?

(ii) Determine the value of the total angular momentum for a 3d electron.

(Paper-2) (Section – A)

### Explanation

(i) Angle do the make with z – axis is given as,

Where, is the z – component of the angular momentum, which is given as,

is the magnetic quantum number. Its value varies from

Here, from question; value of

• And angular momentum is given

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## Question number: 10

» Physical Optics » Polarisation and Modern Optics » Principles of Fibre Optics Attenuation

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Appeared in Year: 2012

Essay Question▾

### Describe in Detail

A step – index silica fiber consists of core of refractive index 1.450 and diameter . If the numerical aperture of the fiber is 0.16, calculate:

(i) the acceptance angle of the fiber,

(ii) refractive index of the cladding, and

(iii) if the fiber is immersed in water of refractive index 1.33, how does the acceptance angle change? (paper -1) (Section – A)

### Explanation

• Here, from question, we can say,

• The numerical aperture of the optical fiber is given as,

• where, is acceptance angle of the fiber. is the refracting medium of surrounding of optical fibe

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