# Electrostatic magnetostatic communication system - Electronics Engineering

## Electrostatic magnetostatic communication system - Electronics Engineering

(1) The reason for a point charge in space to get attracted towards a dielectric material is

(A) Maximization of electrostatic flux
(B) Dielectric hysteresis
(C) Dielectric polarisation
(D) None of the above

(2) Initially the distance between a positive and a negative charge is 4 Cm. When they are moved closer together the distance between them is 1 cm and the force between them will be

(A) 4 times smaller than before
(B) 4 times larger than before
(C) 8 times larger than before
(D) 16 times larger than before

ANSWER: 16 times larger than before

(3) The medium that has least dielectric strength is

(A) Glass
(B) Air
(C) Quartz
(D) Paraffin wax

(4) Inside a hollow spherical conductor

(A) Electric field changes with the distance from the centre of the sphere
(B) Electric field changes with the magnitude of the charge given to the conductor
(C) Electric field is zero
(D) Electric field is constant

(5) In an electric field a dielectric is placed. The field strength will

(A) Reduce to zero
(B) Remain constant
(C) Increase
(D) Decrease

(6) Coulomb’s law for the force between electric charges most closely resembles with

(A) Newton’s law of gravitation
(B) Newton’s law of motion
(C) Law of conservation of energy
(D) Gauss’s theorem

(7) The series equivalent resistance in case of a lossy capacitor will be

(A) Large
(B) Small
(C) Very small
(D) Negligible

(8) With a given dielectric when a parallel plate capacitor is connected to a battery it stores twice as much charge as it does with air as dielectric. The susceptibility of the dielectric is

(A) 2
(B) 1
(C) 3
(D) 0

(9) For a point charge between two conducting plates that are inclined at an angle of 30° to each other, the number of image charges will be

(A) 22
(B) 12
(C) 10
(D) 11

(10) What will be the maximum potential attained by a sphere of one meter radius

(A) 30,000 V
(B) 2000 V
(C) 3 million volts
(D) 1000 V

(11) To measure the dissipating factor of a capacitor the instrument used is

(A) Campbell bridge
(B) Schering bridge
(C) Galvanometer
(D) Potentiometer

(12) When two condensers are connected in series the total capacitance is 0.03μF. When two condensers are connected in parallel the total capacitance is 0.16μF. The ratio of capacitances will be

(A) 4
(B) 3
(C) 2
(D) 1

(13) What will be the value of capacitance when it is charged to 100 V and has 100 μ coulombs of charge?

(A) 10 μF
(B) 100 μF
(C) 10 pF
(D) 100 pF

(14) If the physical dimensions of a mica capacitor and ceramic capacitor are same, which one has the higher value of capacitance?

(A) Ceramic capacitor
(B) Mica capacitor
(C) Both have same value of capacitance
(D) Nothing can be concluded on the basis of given information

(15) On equipotential surface the electric field is

(A) Infinite
(B) Zero
(C) Parallel to the surface
(D) Perpendicular to the surface

(16) Reluctance: Inductance::

(B) AT/Weber : Henry
(C) Ampere turn : Ampere
(D) Mho : ohm

(17) A keeper is used to

(A) Change the direction of magnetic lines
(B) Amplify flux
(C) Restore lost flux
(D) Provide a closed path for flux

ANSWER: Provide a closed path for flux

(18) To make a magnet from soft iron the quickest and the most effective way is by

(A) Placing it inside a coil carrying current
(B) Rubbing with another magnet
(C) The use of permanent magnet
(D) Induction

ANSWER: Placing it inside a coil carrying current

(19) Consider a solenoid that has flux = 12m Wb and flux density = 0.9 tesla. The inside diameter of a solenoid

(A) 1.5 cm
(B) 130 cm
(C) 13 cm
(D) 10 cm

(20) Let the magnetic moment of a rectangular magnet be M. If a rectangular magnet is cut into two places of same length, the magnetic moment of each place will be

(A) 2M
(B) M / 2
(C) M
(D) M / L

(21) For which substance susceptibility is positive

(A) Non-magnetic
(B) Paramagnetic
(C) Ferromagnetic
(D) None of the above

(22) Consider the pole-shoe having its face area of 1.5 cm² and total flux is 0.18 milli-webers. The flux density is the air gap is

(A) 0.12 Tesla
(B) 120 Tesla
(C) 12 Tesla
(D) 1.2 Tesla

(23) Length of conductor = 1.5 meters carries current = 100 amperes at right angle to a magnetic field. Flux density = 0.67 tesla. Force acting on the conductor will be

(A) 100 N
(B) 10000 N
(C) 440 N
(D) 500 N

(24) The eddy current loss of a ferrite core is less than that of an iron core because

(A) Ferrites have high resistances
(B) Ferrites have high hysteresis
(C) Ferrites have low permeability
(D) Ferrites are magnetic

(25) Let a magnet is in motion relative to the coil. The induced emf does not depend upon

(A) Number of turns of the coil
(B) Pole strength of the magnet
(C) Motion of the magnet
(D) Resistance of the coil

(26) Let a ferromagnetic core is subjected to cycles of magnetization. It will exhibit hysteresis when the cycle is

(A) Rotating
(B) Pulsating
(C) Alternating
(D) Any of the above

(27) When a crack is developed in the magnetic path of an inductor, it will result in

(A) Zero inductance
(B) Increased inductance
(C) Reduced inductance
(D) No change in inductance

(28) Degaussing is the process of

(A) Remagnetizing metallic parts
(B) Demagnetizing metallic parts
(C) Removing impurities from materials
(D) Removing gases from materials

(29) L shape is formed by bending a bar magnet at its center. The magnetic moment of the bent magnet will be

(A) 1 / √2 times its original value
(B) √2 times its original value
(C) Half the original value
(D) Same as that of unbent magnet

ANSWER: 1 / √2 times its original value

(30) Whenever a conductor cuts magnetic flux, an emf is induced in that conductor. This statement is due to

(A) Weber and Ewing’s theory
(C) Joule’s law
(D) Coulomb’s law

(31) What will be the time interval between two successive samples when a signal of maximum frequency of 10KHz is sampled at Nyquist rate?

(A) 100μs
(B) 1000μs
(C) 50μs
(D) 5μs

(32) Consider a narrow band signal that occupies a frequency range of nf to (n+1) f (Take n to be an integer). When this signal is to be sampled the maximum sampling rate will be

(A) 2nf
(B) 2(n+1) f
(C) 2 f
(D) None of the above

(33) For the white noise spectral density

(A) Is constant
(B) Varies with bandwidth
(C) Varies with frequency
(D) None of the above

(34) The auto-correlation function of a signal (t) at t0 = 0 is equal to

(A) Average voltage of the signal
(B) Average power of the signal
(C) Infinite
(D) Zero

ANSWER: Average power of the signal

(35) For a thermal noise probability density function is

(A) Poisson
(B) Binomial
(C) Gaussian
(D) None of the above

(36) Redundancy in communication system

(A) Helps to correct errors
(B) Helps to detect errors
(C) Reduces efficiency of communication
(D) All of the above

(37) In a continuous signal, the amount of information is

(A) 0
(B) 2 bits
(C) 4 bits
(D) Infinite

(38) Different signals in a TDM system are distinguished from each other

(A) In amplitude
(B) In time
(C) In frequency
(D) Both in time and frequency

(39) Each of the n signals is band limited to Fm Hz by TDM. To transmit this signal minimum bandwidth required will be

(A) N Fm
(B) 2 Fm
(C) Fm
(D) None of the above

(40) Quadrature multiplexing is a form of

(A) Frequency division multiplexing
(B) Time division multiplexing
(C) Combined Frequency and time division multiplexing
(D) None of the above