A coil of wire is arranged with its plan perpendicular to a uniform magnetic field o flux density B. when the radius of the coil increases from r1 to r2 in time ?t then what is the emf induced in the coil?
1.?B/r22-r12/?t
2.?B(r2-r1)2/?t
3.?B(r22-r12)/?t
4.?B(r22+r12)/?t
A metal rod of 25 cm length is moving at a speed of 0.5/sec in direction perpendicular to 0.25T magnetic field. Emf produced in the rod is
1.0 volt
2.3.125 volt
3.31.25 volt
4.0.03125 volt
A small coil lies inside a large coil. The two coils are horizontal concentric and carry currents in opposite directions. The large coil will experience
1.A torque about horizontal axis
2.A torque about vertical axis
3.An upward force along the axis
4.No resultant force
A.C can not be used for
1.producing heat
2.producing light
3.Magnetizing iron
4.Producing magnetic field
Acceptor and donor impurities donate
1.n-carriers only
2.p-carriers only
3.p-carriers and n-carriers respectively
4.n-carriers and p-carriers respectively
An aeroplane of wingspan 10m flies from the equator towards the North Pole. The wings are perpendicular to the vertical component of the earths magnetic field (B = 4x10-5T). At maximum speed an emf of 96mV is induced across the wing tips. The maximum speed of the aeroplane is
1.150msec-1
2.384msec-1
3.38.4msec-1
4.200msec-1
An electric current induced within the body of a conductor when that conductor either moves through a non uniform magnetic field or in a region where there is a change in magnetic flux is called
1.Induced current
2.Eddy current
3.Back emf
4.None of the above
Depletion region of a junction is formed
1.during the manufacturing process
2.under forward bias
3.under reverse bias
4.when temperature varies
Electrons present in p-type material due to thermal pair generation are
1.majority carriers
2.minority carriers
3.dual carriers
4.blockers
For long distance transmission the transformer used is
1.Step down
2.Input voltage and output voltage remain same
3.Step up
4.Amplifier is used
Forward current through a semi conductor diode circuit is due to
1.minority carriers
2.majority carriers
3.holes
4.electrons
Hole is equivalent to
1.a negative charge
2.a positive charge
3.a neutral particle
4.an electron
Identify the correct statement about minority carriers
1.holes in n-type and free electrons in p-type
2.holes in n-type and p-type
3.free electrons in n-type and holes in p-type
4.free electrons in n-type and p-type
In a half-wave rectifier the r.m.s. value of the A.C. component of the wave is
1.Equal to D.C. value
2.More than D.C. value
3.Less than D.C. value
4.Zero
In full wave rectification the output D.C. voltage across the load is obtained for
1.The positive half cycle of input A.C.
2.The negative half cycle of input A.C.
3.The complete cycle of input A.C.
4.All of the above.
In half-wave rectification the output D.C. voltages is obtained across the load for
1.The negative half cycle of A.C.
2.The positive half cycle of A.C.
3.The positive and negative half cycles
4.Either positive or negative half of A.C.
In n-p-n transistor, p works as
1.collector
2.emitter
3.base
4.any of above
In p-n-p transistor the collector current is
1.equal to emitter current
2.slightly less than emitter current
3.greater than emitter current
4.any of above
In the transistor schematic symbol, the arrow
1.is located on the emitter
2.is located on the base
3.is locate on the collector
4.points form north to south
Lagging of changes in the magnetization of a substance behind changes in the magnetic field as the magnetic field is varied is known as magnetic
1.Retaintivity
2.Permeability
3.Flux
4.Hysteresis
Long distance transmission is easy for
1.D.C voltage
2.A.C voltage
3.Half A.C voltage
4.Half D.C voltage
Magnetic compass needle will be deflecting if it is kept near
1.Static charge
2.Soft iron
3.Semi-conductor
4.Accelerating charge
Non inductive resistances are used in decreasing
1.Mutual inductance
2.Self inductance
3.Magnetic fields
4.Heating effect
p-n junction when reversed biased acts as a
1.capacitor
2.inductor
3.on switch
4.off switch
Self inductance of a long solenoid is
1.??n2?A
2.??n2A/?
3.??N2?A
4.BA
Semi-conductor germanium and silicon are
1.pentavalent
2.trivalent
3.divalent
4.tetravalent
Semi-conductors with donor atoms and free electrons belong to the type
1.n
2.p
3.mix
4.any of above
The alternating current has frequency of 106 Hz in such a way that time period for completion of cycle is
1.1?s
2.1.5?s
3.106sec
4.1sec
The alternating voltage is an example of
1.A digital waveform
2.An analogue waveform
3.Discrete waveform
4.None at all
The device or circuit used for conversion of A.C. into D.C. is called
1.An amplifier.
2.A rectifier
3.Filtering circuit
4.Converter.
The device used for conversion of D.C. to A.C. is called
1.Converter
2.A rectifier
3.Inverter
4.Oscillator
The emf induced in a coil by a changing magnetic flux may have unit as
1.ms-1A
2.ms-2A-1
3.kgms2A-1
4.kgm2s-1A-1
The emf induced in a conductor of unit length moving with unit velocity at right angles to a magnetic field is equal to
1.Magnetic flux density
2.Torque
3.Mutual induction
4.Motional emf
The especially designed semiconductor diodes used as indicator lamps in electronic circuits are
1.The switch
2.The light emitting diode
3.The photo diodes
4.Solar cells.
The operational amplifier is
1.A high gain amplifier
2.A high-power amplifier
3.A high resistance amplifier
4.A low resistance amplifier
The out put voltage of a transformer is 3 times the input voltage then turns ratio will be
1.03-Jan
2.3
3.1
4.6
The rectangular voltage is an example of
1.An analogue waveform
2.Continuous wave form
3.Electronic waveform
4.A digital waveform
The self-inductance of a solenoid is increased when a soft iron core is inserted into it. This is because the soft iron core
1.Decreases the resistance of the solenoid
2.Reduces the effect of eddy current
3.Improves the flux linkage between the turns of the coil
4.Increases the mutual inductance between the solenoid and the core
The semiconductor diode can be used as a rectifier because _
1.It has low resistance to the current flow when forward biased & high resistance when reverse biased.
2.It has low resistance to the current flow when forward biased.
3.It has high resistance to the current flow when reverse biased
4.Its conductivity increases with rise of temperature.
The simplest type of rectification known as half wave rectification is obtained by
1.using a transistor
2.suppressing the harmonics in A.C voltage
3.suppressing half wave of A.C supply by using diode
4.using a Coolidge tube
The specially designed semi-conductor diodes used as fast counters in electronic circuits are
1.The light emitting diodes
2.Photo diodes
3.Photo voltaic cell
4.Solar cells.
The value of resistivity for insulator is of the order of
1.105 ohm metre
2.106 ohm metre
3.107 ohm metre
4.108 ohm metre
The velocity of an oscillating charge as it moves to and fro along a wire is always
1.constant
2.zero
3.changing
4.infinite
Thermions are
1.protons
2.positrons
3.electrons
4.photons
Transformer works on the principle of
1.Lenzs law
2.Faradays law
3.Mutual induction
4.Law of conservation of power
When the motor is at its maximum speed then back emf will be
1.Maximum
2.Zero
3.Intermediate values
4.No back emf
Which one of following band is completely filled in case of conductors?
1.Conduction band
2.Fermi band
3.Valence band
4.Forbidden band
Which one of the following devices does not function like an electric motor?
1.Galvanometer
2.Ammeter
3.Voltmeter
4.Transformer
Which one of the following has the greatest energy gap?
1.insulator
2.conductor
3.semi conductor
4.any of above
Which one of the following is not a donor impurity?
1.antimony
2.phosphorus
3.aluminium
4.arsenic