Components

Q. A spherical capacitor consists of two concentric spherical conductors, held in position by suitable insulating supports (Fig.). Show that the capacitance of a spherical capacitor is given by $C=\frac{4\pi {\epsilon }_0{r}_1{r}_2}{r_1-r_2}$, where $r_1\text{and}{r}_2$ are the radii of outer and inner spheres, respectively.

Q. The angle between the direction of propagation and the plane of polarisation is 0 degree(not 90) . Why?

Q.

A LASER is a source of very intense, monochromatic, and unidirectional beam of light. These properties of a laser light can be exploited to measure long distances. The distance of the Moon from the Earth has been already determined very precisely using a laser as a source of light. A laser light beamed at the Moon takes 2.56 s to return after reflection at the Moon’s surface. How much is the radius of the lunar orbit around the Earth?

Q. The charges $Q,2Q\text{and}4Q$ are uniformly distributed in three dielectric solid spheres of radii $R/2,R\text{and}2R$ respectively as shown in the figure. If the magnitudes of electric field at the point $P$ at a distance $R$ from the centre of the spheres $\text{I, II}$ and $\text{III}$ are $E_1,E_2\text{and}{E}_3$ respectively, then

1. $E_1>E_2>E_3$
2. $E_3>E_2>E_1$
3. $E_2>E_1>E_3$
4. $E_3>E_1>E_2$

Q. Name the essential components of a communication system.

Q. in He–Ne laser, metastable state exist in (1)He (2)Ne (3)both 1 and 2 (4) non

Q. Sea water at frequency $v=4\times {10}^{8}Hz$ has permittivity $ϵ\approx 80{ϵ}_0$, permeability $\mu \approx {\mu }_0$ and resistivity $\rho =0.25\Omega -m$. Imagine a parallelplate capacitor immersed in sea water and driven by an alternating voltage source $V\left(t\right)=V_0\sin \left(2\pi vt\right)$. What fraction of the conduction current density is the displacement current density?

Q. Which basic mode of communication is used for telephonic communication?

Q. Read the following two statements below carefully and state, with reasons, if it is true or false.

A The Young’s modulus of rubber is greater than that of steel.

B The stretching of a coil is determined by its shear modulus.

Q. Draw a block diagram of a generalized communication system. Write the functions of each of the following:
(a) Transmitter
(b) Channel
(c) Receiver

Q.

A laser device produces amplification in the

1. microwave region

2. ultraviolet or visible region

3. infrared region

4. None of the above

Q. Name the three basic elements of a communication system.

Q. Broadcasting antennas are generally

1. Omni directional type
2. Vertical type
3. Horizontal type
4. None of these

Q. The work function for the following metals is given Na: $2.75eV;K:2.30eV;Mo:4.17eV;Ni:5.15eV$. Which of these metals will not give photoelectric emission for a radiation of wavelength $3300\stackrel{\circ }{A}$ from a He −Cd laser placed 1 m away from the photocell? What happens if the laser is brought nearer and placed $50\text{cm}$ away?

Q. Digital signal

1. do not provide a continuous set of values
2. represent value as discrete steps
3. can utilize binary system and
4. can utilize decimal as well as binary systems

Q. Broadcasting antennas are generally

1. Omni directional type
2. Vertical type
3. None of these
4. Horizontal type

Q. A basic communication system consists of:
A)Transmitter , B)Information Source , C)User of Information, D)Channel , E) Receiver.
Choose the correct sequence in which these are arranged in a basic communication system.

1. A, B, C, D, E
2. B, A, D, E, C
3. B, D, A, C, E
4. B, E, A, D, C

Q. An electron gun with its collector at a potential of $100V$ fires out electrons in a spherical bulb containing hydrogen gas at low pressure $(\sim {10}^{–2}\text{mm}$ of Hg). A magnetic field of $2.83\times {10}^{–4}T$ curves the path of the electrons in a circular orbit of radius $12.0\text{cm}$. (The path can be viewed because the gas ions in the path focus the beam by attracting electrons and emitting light by electron capture; this method is known as the ‘fine beam tube’ method.) Determine $\frac{e}{m}$ from the data.

Q. Laser beams are used to measure long distances because

1. They are monochromatic
2. They are highly polarised
3. They are coherent
4. They have high degree of parallelism

Q.

Television signals reach us only through the ground waves. The range $R$ related to the transmitter height $h$ is in proportion to

1. $h$

2. $h^{\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}$

3. $h^{\raisebox{1ex}{$-1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}$

4. $h^{-1}$

Q. Laser light is considered to be coherent because it consists of

1. Many wavelengths
2. Uncoordinated wavelengths
3. Cooridnated waves of exactly the same wavelength
4. Divergent beams

Q. The maximum distance up to which TV transmission from a TV tower of height h can be received is proportional to ?

Q. Name the essential components of a communication system

Q. What are the three essential part of a communication system?

1. transmitter, channel and receiver
2. transmitter , noise and channel
3. information source , transmitter and channel
4. transmitter, information source and receiver

Q. two towers on top of two hill are 40km apart the line joining them passes 50m above a hill halfway btw the towers .longest wavelength of radio waves which can be sent btw the towers .longest wavelength of radio wave which can be sent btw the towers without appreciable diffraction is

Q. Which network is a packet switching network?

1. Ring network
2. LAN
3. Star network
4. EuroNET
5. None of the above

Q. Why cant we see stars during the day?

Q.

A device for producing intense and coherent (waves in step) beam of light is called

1. laser

2. maser

3. search light

4. none of the above

Q. A basic communication system consists of
a) Transmitter
b) Information source
c) User of information
d) Channel
e) Receiver

1. a, b, c, d and e
2. b, e, a, d and e
3. b, d, a, c and e
4. b, a, d, e and c

Q. What is broadcast communication?