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MCQs on Electromagnetic Fields

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01․ Two parallel plates are separated by a distance D charged by V volt. The field intensity E is given by,
V × D
V / D
V × D²
V² / D

Electric field intensity between two points is always expressed as the potential difference between these two points divided by the distance between them. The strength of electric field or electric field intensity is measured by volt per meter or newton per meter.
02․ The right hand rule for determining the direction of the induced EMF was introduced by
Faraday
Lenz
Fleming
Maxwell

The right hand rule for determining the direction of induced EMF was introduced by Fleming and it is well known as Fleming’s right hand rule. It is used to find the direction of induced emf of a generator.
03․ Whenever the magnetic flux changes with respect to an electric conductor or a coil, an EMF is induced in the conductor is Faraday’s
first law
second law
third law
fourth law

Faraday’s law of electromagnetic induction states
  1. Whenever a changing flux links with a conductor, there will be an EMF induced in the conductor.
  2. The magnitude of this induced EMF is directly proportional to the rate of change of flux linkage with respect to time.
These two statements are well-known as Faraday’s first and second law of electromagnetic induction respectively.
04․ Which of the following represents ohms law
V = RI
J = σE
I = GV
All of the above

These are the different forms to represent the ohms law.
05․ Conductor is static and the field is varying then emf will be induced. This principle is called
virtually induced emf.
dynamically induced emf.
static induced emf.
none of these

According to the Faraday's law of electromagnetic induction principle, the emf will be induced whenever conductor cuts a varying field or vice versa. The emf will be induced when an alternating magnetic field cuts the rotor conductor.
06․ As a result of reflection from a plane conducting wall, electromagnetic waves acquire an apparent velocity greater than the velocity of light in space. This is called the
velocity of propagation.
normal velocity.
group velocity.
phase velocity.

The phase velocity of a wave is the rate at which the phase of the wave propagates in space. This is the speed at which the phase of any one frequency component of the wave travels. Basically, the speed of this velocity is greater than the velocity of light in space.
07․ Two infinite parallel metal plates are charged with equal surface charge density of the same polarity. The electric field in the gap between the plates is
same as that produced by one plate.
double the field produced by one plate.
dependent on coordinates of field points.
zero.

The equal surface charge densities are having same charge either positive or negative. So, same charge repels each other. Hence, the resultant electric field in the gap between the plates is zero.
08․ Inside a hollow conducting sphere
electric field is zero.
electric field is a non zero constant.
electric field changes with magnitude of the charge given to the conductor.
electric field changes with distance from the center of the sphere.

For any conducting sphere, the charge enclosed is zero and hence, the electric field inside it is zero. This is an application of the Gauss Law. In fact Gaussian surface includes no charges inside it.
09․ Electric field intensity (E) at ant point in an electric field is equal to
potential gradient.
(potential gradient)2.
(potential gradient)1/2.
(potential gradient)1/3.

The total electric field at any point is equal to the vector sum of the separate electric fields that each point charge would create in the absence of the others. That is, width=231 The electric field is nothing but the potential gradient of that particular point.
10․ A conductor of length L has current I passing through it, when it is placed parallel to strong magnetic field. The force experienced by the conductor will be
BIL.
BL2I.
BI2L.
zero.

The force can be found with the given expression F = I × L × B × sinθ and θ is the angle between I and B. When that current carrying conductor is placed parallel to the magnetic field, then the angle between current and magnetic field is zero. So, sinθ = sin0° = 0. Hence, the force experienced by the conductor is zero.
11․ The force between two long parallel conductors is inversely proportional to
radius of conductors.
current in one conductor.
product of current in two conductors.
distance between the conductors.

If the current is flowing through the two different conductors ‘d’ distance apart, in the same direction, then the force between the two conductors is directly proportional to the product of the currents and inversely proportional to the distance between the two conductors.
12․ In the left hand rule, forefinger always represents
voltage.
current.
magnetic field.
direction of force on the conductor.

Thumb finger represents the direction of force, Fore finger represents the direction of magnetic field, middle finger represents the direction of current.
13․ A wire carrying current is bent in the form of a circular loop. Then the magnetic field around each portion of the wire will be
parallel to the plane of the wire.
perpendicular to the circumference of the wire.
parallel to half portion and perpendicular for the other half.
none of above.

Suppose the straight wire is bent in the form of a circular loop, current flows through every point on the wire that would give rise to the magnetic field appearing as straight lines at the center of the circular loop. By applying the right hand rule, it is easy to check that every section of the wire contributes to the magnetic field lines in the same direction within the loop.
14․ Cork Screw rule is used to find
direction of current.
direction of magnetic field.
direction of electric field.
direction of emf.

The direction in which the head of the cork screw rotates that would give the direction of the magnetic field or magnetic force of lines. The shape of this magnetic field is circular and the direction of magnetic field is clock-wise.
15․ Two long parallel conductors carry 100 A. If the conductors are separated by 20 mm, the force per meter of length of each conductor will be
100 N.
0.1 N.
1 N.
0.01 N.

Current I1 and I2 = 100 Amps, Distance = 20 mm = 20 × 10-3 m, Force = ? The force is found by the following expression
16․ The field at any point on the axis of a current carrying coil will be
at angle of 45° with the axis.
perpendicular to the axis.
parallel to axis.
zero.

A continuous current in a current carrying coil is divided into multiple current elements. Using the superposition principle and the Biot-Savarts law, each discrete element generates its own magnetic field and when it is integrated with each field that produces a resultant field and it is aligned parallel to the axis of the coil.
17․ Two straight parallel conductors carry equal currents in opposite direction. The force between them is
repulsive.
attractive.
zero.
none of above.

When two current carrying conductors are placed parallelly, there will be a force acting between them. The force is attractive if direction of currents in the conductor is same and it is repulsive if the direction of the currents is opposite. This can easily be explained by right hand rule.
18․ The change of cross sectional area of conductor in magnetic field will affect
reluctance of conductor.
resistance of conductor.
(A) and (B) both in the same way.
none of above.

We know that the cross sectional area is inversely proportional to the resistance of the conductor. In magnetic circuits, reluctance is analogous to the resistance. Hence, the resistance and reluctance would be affected in the same way.
19․ A point pole has a strength of 4π × 10-4 weber. The force in newtons on a point pole of 4π × 1.5 × 10-4 weber placed at a distance of 10 cm from it will be
15 N.
20 N.
7.5 N.
3.75 N.

Given data: Pole strength m1 = 4π × 10-7 Weber m2 = 4π × 1.5 × 10-4; r = 10 cm. We know that the force is found by the below expression,
20․ Biot-Savarts law states the relation between magnetic intensity and
filament current only.
surface current only.
(A), (B), and (D) are all correct.
volume current only.

Biot-Savarts law states that the differential magnetic field intensity dH produced at a point P by the differential current element Idl. This is the only one law is available to relate the magnetic intensity and the different type of current distribution. The given equations show the different relations between the magnetic intensity and the currents.
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