Physics

Magnetism and Electromagnetism

1,011 Questions

This hub provides practice questions on magnetism and electromagnetism. It covers magnetic flux density, electromagnets, magnetic lines of force, and electromagnetic induction. These physics concepts frequently appear in technical and non-technical competitive exams.

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Magnetism and Electromagnetism Questions

Multiple choice physics properties of a magnetic field earth - a gigantic magnet magnetic field of earth introduction to magnetic field and magnetic flux

Atoms or molecules of liquid or gaseous mate-rial are in rapid motion and are not aligned. Thus,

  1. Fluids can be easily magnetised

  2. Fluids can never be magnetised

  3. Liquid iron rotating about an axis in earth's core is an exception

  4. Liquid iron rotating about an axis in earth's core is difficult to be magnetised
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

As the material gets heated or it is in its liquid or gaseous state, the atoms or molecules are in rapid motion and are not aligned. Thus, fluids are seldom magnetic. An exception is when a magnetic material such as iron is in its liquid state and is continuously rotating around the axis; the atoms can be aligned in one direction, even though they are in liquid rapid motion.

Multiple choice physics properties of a magnetic field earth - a gigantic magnet magnetic field of earth introduction to magnetic field and magnetic flux

When a Magnetic needle is suspended freely, it always aligns itself in the direction of magnetic north and south pole of the earth, the north pole of the needle gets attracted towards the magnetic south pole of the earth and the south gets repelled equally away from it. So two equal and opposite forces acting on the needle should cancel each other which does not happen because the:

  1. Force of attraction and repulsion are equal but not exactly in opposite direction

  2. Force of attraction and repulsion are not exactly equal even though in opposite direction

  3. Force of attraction and repulsion are not equal and not in opposite direction

  4. Force of attraction and repulsion are exactly equal and opposite in direction
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Though two equal and opposite forces are acting on the needles, they don't cancel each other as they act on two different points and they generate torque which later at proper alignment reaches equilibrium such as

$\sum F=0$ and

$\sum M=0$


Multiple choice ac and dc ac vs dc electro-magnetism effects of electric current physics

Identify the two types of current exist in physics.

  1. direct and alternating

  2. indirect and alternating

  3. direct and attenuating

  4. directive and alternative

  5. none of the answers are correct
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

There exists two types of current -  direct current (dc) and alternating current (ac).

Direct current has constant magnitude and direction whereas the alternating current keeps reversing its direction at regular intervals.

Multiple choice ac and dc ac vs dc electro-magnetism effects of electric current physics

$AC$ and $DC$ can be distinguished using.

  1. heating effect

  2. magnetic effect

  3. chemical effect

  4. none of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

It is possible to distinguish the AC and DC using magnetic effect. Both AC and DC can produce magnetic field but only AC can produce a varying magnetic field. So, using DC, current cannot be induced into another conductor. It can only be done using AC.

Multiple choice physics properties of material substances elastic behaviour of solids elastic and plastic substances properties of substances

The plasticity behaviour of a material determines the 

  1. elastic behavior of the material

  2. resistance of the material to electric fields

  3. viscous behavior of the material and is irrecoverable.

  4. resistance of the material to magnetic fields
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Plasticity is defined as the property which enables a material to be deformed continuously and permanently without rupture during the application of force. This deformation determines the viscous behavior of the material and is irrecoverable.

Multiple choice physics option a: relativity maxwell's equations the nature of light introduction to electromagnetic waves

Maxwell in his famous equations of electromagnetism, introduced the concept of

  1. ac current

  2. displacement current

  3. impedance

  4. reactance
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Maxwell's equations are:

1. $\nabla .E=\rho / \epsilon$
2. $\nabla.B=0$
3. $\nabla \times E= -\dfrac{dB}{dt}$
4. $\nabla \times B= \mu _0J+ \dfrac{1}{c^2} \dfrac{dE}{dt}$
so, considering the last eqn. written,
$\nabla \times B=\mu _0 J$ is the Ampere's eqn.
so, Maxwell modified the Ampere's eqn. and introduced the concept of displacement current.
So, displacement current =$\dfrac{1}{c^2} \dfrac{dE}{dt}$

Hence the correct option is $(B)$

Multiple choice physics option a: relativity maxwell's equations the nature of light introduction to electromagnetic waves

Maxwell's equation describe the fundamental laws of

  1. electricity

  2. magnetism

  3. mechanics

  4. both (A) and (B)
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Maxwell's equation describe the fundamental laws of electricity and magnetism. His equations describe how electric and magnetic fields are generated and altered by each other and by charges and currents.

Multiple choice physics option a: relativity maxwell's equations the nature of light introduction to electromagnetic waves

According to Maxwell's hypothesis, a changing electric field gives rise to

  1. an electromagnetic force

  2. electric displacement current

  3. magnetic field

  4. pressure gradient
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
$Answer:-$ C option
$\nabla \times B={ \mu  } _{ 0 }(J+{ \epsilon  } _{ 0 }\dfrac { dE }{ dt } )$
using this equation of maxwell we can say changing electric field $\dfrac{dE}{dt}$ induces magnetic field.
Multiple choice physics option a: relativity maxwell's equations the nature of light introduction to electromagnetic waves

Which of the following conclusion can be drawn from the result $\oint \bar{B}\cdot d\bar{A}=0$

  1. Magnetic field is zero everywhere

  2. Magnetic monopole cannot exist

  3. Magnetic lines of force do not intersect each other

  4. A current produces magnetic field
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Flux of certain closed surface is zero and so it tells that net magnetic charge is equal to zero. This is possible when there are two equal and opposite poles.

Multiple choice physics option a: relativity maxwell's equations the nature of light introduction to electromagnetic waves

According to Maxwell's hypothesis, changing of electric filed give rise to

  1. magnetic field

  2. pressure gradient

  3. charge

  4. voltage
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

According to Maxwell's hypothesis, changing of electric field gives rise to Magnetic field.

We know that $F=qE,$, where $F$ is force and $E$ is electric field.
We can relate magnetic field and force by $F=qvB$, where $v$ is velocity and $B$ is the magnetic field.
Therefore we can obtain magnetic field by changing electric field.
Therefore option $A$ is correct.

Multiple choice physics magnetic effect of electric current fleming's left hand rule magnetic force magnetic force on a moving charge and current carrying wire

You are sitting in a room in which a strong magnetic field is directed from your left towards right. A beam of electrons is directed from front towards you. What would be the direction of magnetic force on this beam ?

  1. downwards.

  2. upwards.

  3. towards right

  4. towards left

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
The direction of the magnetic field is from left to right, the direction of the beam of electrons is from your front hence the direction of the current is from back to front. Now by applying Fleming left hand rule we can find that the direction of the magnetic force on the beam of electron is downwards.
Multiple choice physics magnetic effect of electric current fleming's left hand rule magnetic force magnetic force on a moving charge and current carrying wire

An electric current runs counterclockwise in a rectangular loop around the outside edge of the page which lies flat on your table. A uniform magnetic field is then turned on directed parallel to the page from the top to bottom. The magnetic force on the page will cause:

  1. the left edge to lift up

  2. the right edge to lift up

  3. the top edge to lift up

  4. the bottom edge to lift up
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Current is flowing anticlockwise in the rectangular loop and in the upper edge of page current is flowing towards left and magnetic field is from top to bottom , so by applying Fleming's left hand rule the direction of force is found to be in the upward direction, lifting the top edge up.

Multiple choice physics magnetic effect of electric current fleming's left hand rule magnetic force magnetic force on a moving charge and current carrying wire

A positive charge is at rest in a uniform magnetic field directed to the right. What force does the positive charge feel, due to the magnetic field?

  1. An upward force.

  2. A downward force.

  3. A force to the left.

  4. No force is felt.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
For experiencing a magnetic force on a charge  particle, the particle should move in the magnetic field with some velocity. As the velocity of the particle is zero so, the force on the particle is also zero.
Multiple choice physics magnetic effect of electric current fleming's left hand rule magnetic force magnetic force on a moving charge and current carrying wire

The direction of force on a current carrying conductor placed in a magnetic field is given by :

  1. Fleming's Left Hand Rule

  2. Fleming's Right Hand Rule

  3. End Rule

  4. Right Hand Palm Rule
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The direction of this force is always right angles to the plane containing both the conductor and the magnetic field, and is predicted by Fleming’s Left-Hand Rule.