# Optionals IAS Mains Physics: Questions 249 - 254 of 307

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## Question 249

Appeared in Year: *2009*

### Describe in Detail

Essay▾What are the important properties of a hologram? (Marks 6)

### Explanation

- In an ordinary photography each region contains separate and individual part of the original object. On the other hand, in a hologram each part contains information about the entire object. From even a small part of the hologram the entire image can be reconstructed if only with a reduced clarity and definition of image. Therefore, a hologram is a …

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## Question 250

Appeared in Year: *2011*

### Describe in Detail

Essay▾Draw the common – base amplifier circuit, using an transistor and briefly discuss its working. (Marks 15)

### Explanation

In common base configuration, input is connected between emitter and base and output is taken across collector and base. This base is common between input and output circuits.

The common – base amplifier provides high voltage gain with a maximum current of . Since it has a low input resistance, the amplifier is the most appropriate type for certa…

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## Question 251

Appeared in Year: *2011*

### Describe in Detail

Essay▾Find an expression for lattice specific heat of solids and its low and high temperature limits. What is Debye temperature?

### Explanation

If the interatomic distance is small as compared to the wavelength of elastic waves, the crystal can be regarded as a continuum from the point of view of the wave. Based on this idea, Debye assumed that the continuum model is applicable to all the possible vibrational modes of the crystal. Further, the fact that the crystal consists of a finite num…

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## Question 252

Appeared in Year: *2009*

### Describe in Detail

Essay▾Deduce the missing order for a double slit Fraunhofer pattern, if the slit widths are 0.16mm and 0.8mm apart. (Paper I Marks - 5)

### Explanation

- The direction of interference maxima is given by the equation
- The direction of diffraction minima is given by equation

If the value of a and b are such that both the equation are satisfied simultaneously for the same value of , then the position of certain interference maxima correspond to the diffraction minima at same position on the screen.

If P =…

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## Question 253

Appeared in Year: *2009*

### Describe in Detail

Essay▾Obtain Poiseuille՚s equation for a viscous fluid flowing though a narrow tube of radius r and length l. It a spherical body of radius a is allowed to move at a speed though the same viscous fluid of viscosity , show that the visons force will increase with the speed linearly. (Paper-II Marks - 15)

### Explanation

- Let a liquid of coefficient of viscosity be flowing through a narrow horizontal tube of radius r and length l and the velocity gradient will be . In accordance with Newton՚s law of viscous flow, the backward dragging force on the imaginary liquid shell is given by A is the surface area of the shell, equal to
- And, if the pressure difference across…

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## Question 254

Appeared in Year: *2009*

### Describe in Detail

Essay▾Two bodies of masses are placed at a distance d apart. Show that at this position where the gravitational field due to them is zero, the potential is given by, (Paper I Marks - 10)

### Explanation

Let the gravitational field E be zero at a point distant from mass and therefore ) from mass Then clearly,

Hence, potential at the point due to the two masses

Or, potential at the point