# Class 12th Physics – 4 Moving charges and magnetism MCQs

#### The angle between the direction of angular momentum of an electron and the direction of its magnetic momentum is ____.

Correct! Wrong!

The direction of angular momentum of an electron is in opposite direction to the magnetic moment. Thus the angle between them is 180o.

#### The radius of curvature of a charged particle moving in a uniform magnetic field is inversely proportional to ____. The radius of curvature of a charged particle moving in a uniform magnetic field is inversely proportional to ____.

Correct! Wrong!

When a charged particle is projected perpendicular to the magnetic field, the charged particles moves in circular path and the radius of curvature of the circular path is, r=mv/Bq Thus, r∝1/q

#### In hospitals, the radioactive substances used in diagnosis and treatment are produced by using ____.

Correct! Wrong!

The cyclotron is used to bombard nuclei with energetic particles by accelerating it. It is also used to produce artificial radioactive isotopes which can be used in diagnosis and treatment.

#### A current carrying conductor of length 2m experiences a force of 20N when placed perpendicular to direction of magnetic field of induction 4T. Then the current in the conductor is ____.

Correct! Wrong!

Length of the conducting wire, l=2m
The magnetic field induction, B=4T
Force acting on the current carrying conductor, F=20N
The force acting on the current carrying conductor perpendicular to the magnetic field, F=Bil
20=4×i×2
i=208
i=2.5A

#### A moving coil galvanometer can be converted to voltmeter by connecting ____.

Correct! Wrong!

The galvanometer can be converted to voltmeter by connecting a large resistance in series to the galvanometer.

#### A beam of electrons passes un-deflected through mutually perpendicular electric and magnetic fields. If the electric field is switched off and the same magnetic field is maintained. The electrons move in ____.

Correct! Wrong!

When the force due to electric field and magnetic field are equal an in opposite direction, the electrons move without any deviation. When the electric field is switched off, the electrons entered into the magnetic field with 90o.Then the electrons move in a circular path.

#### A spring is held vertically downward and a current i is passed through it. Then the length of the spring____.

Correct! Wrong!

A spring is nothing but a solenoid. When current passing through the solenoid, the adjacent loops behave like magnetic dipole with opposite poles facing each other. Then the adjacent loops attract each other and the length of the spring decreases.

#### When current passing through a conducting wire, a compass needle placed near the conducting wire is moved away from the conductor, then the deflection of the compass needle ____

Correct! Wrong!

The strength of the magnetic field due to a current carrying conductor is maximum near to the conductor; hence the compass needle deflects more. If the compass needle is moved away from the current carrying conductor, the strength of the magnetic field due to the current in the conductor decreases. Hence the deflection of the compass needle decreases.

#### The source of a magnetic field is ____.

Correct! Wrong!

An isolated magnetic pole does not exist. Static electric charges can produce only electric field but not the magnetic field. Current in a conductor or loop produces magnetic field around it in the form of closed loops. Magnetic substances can be attracted by the magnets. But cannot produce magnetic field.

#### A compass needle is placed below a straight conducting wire. If current is passing through the conducting wire from North to South. Then the deflection of the compass is ____.

Correct! Wrong!

When a compass needle is placed below a straight conducting wire. If the current direction is from North to South. Then the compass deflects towards East.

#### A homogeneous electric field E and a uniform magnetic field B are pointing in the same direction. A proton is projected with its velocity parallel to the electric field, then the proton ____.

Correct! Wrong!

The force acting on a charged particle due to only electric field is in the direction of electric field. The force acting on charged particles due to only magnetic field is perpendicular to the plane of magnetic field and the direction of the charged particle. When the magnetic field is turned off in the homogeneous field, the proton continues to move in the same direction with increasing velocity.

#### A compass needle placed near a current carrying conductor shows some deflection. If the strength of the current passing though the conducting wire is doubled, the deflection in the compass needle ____.

Correct! Wrong!

from the Oersted experiment, it was cleared that when current passing through a conductor increases, the strength of the magnetic field produced also increases. Hence the deflection in the magnetic compass increases.

#### The relation between electricity and magnetism was first observed by ____.

Correct! Wrong!

Hans Christian Oerstead was the first scientist, who observed the relation between electricity and magnetism in 1820. Before that, it was believed that, electricity and magnetism are two different branches of physics.

#### When a charged particle is projected into a uniform magnetic field with an angle θ, the force acting on the charged particle is zero. Then the value of θ is ____.

Correct! Wrong!

When a charged particle is projected into a uniform magnetic field with a velocity v and motion of the particle is making an angle θ with the magnetic field, the force acting on the charged particle is, F=Bqvsinθ. The force acting on the charged particle will be zero, when sinθ=0 this is possible, when θ=0o or 180o.

#### Consider the following two statements about the Oersted's experiment. Statement P: The magnetic field due to a straight current carrying conductor is in the form of circular loops around it. Statement Q: The magnetic field due to a current carrying conductor is strong at far points from the conductor, compared to the near points.

Correct! Wrong!

According to the statement P, The magnetic field due to a straight current carrying conductor is in the form of circular loops around it. The conducting wire produces magnetic field around it in the form of concentric circular loop with conducting wire at the center of the loops. Hence, the statement P is true. According to the statement Q, The magnetic field due to a current carrying conductor is strong at far points from the conductor, compared to the near points. But, as we move away from the conducting wire, the strength of the magnetic field decreases. Hence the statement Q is false.

#### The colored, flashing lights called Aurora Borealis is observed at ____.

Correct! Wrong!

During the solar flare. a large number of charged particles like electrons and protons are ejected from the sun. Some of these charged particles are trapped by the earth's magnetic field and moved along the field lines in helical paths. When these particles come closer to the poles the density increases and the collide with atoms and molecules of the atmosphere. These exited atoms emit colorful light.This phenomenon occurred at north pole is called Aurora Borealis and at the south pole, it is called Aurora Australis.

#### Consider the following statements about the motion of a charged particle in a uniform magnetic field: Statement P: The path executed by a charged particle whose motion is perpendicular to the magnetic field is a helix. Statement Q: The path executed by a charged particle whose motion is neither perpendicular nor along the magnetic field is a circle.

Correct! Wrong!

For the statement P, The path executed by a charged particle whose motion is perpendicular to the magnetic field is not a helix. It is a circle. Hence the statement P is false. For statement Q, The path executed by a charged particle whose motion is neither perpendicular nor along the magnetic field is not a circle. It is a helix. Hence the statement Q is false.

#### The magnetic field induction due to a small current element at a point making an angle θ with the conductor is inversely proportional to ____.

Correct! Wrong!

We know that the magnetic field due to a current element is, (dB=μ0/4π) × idlsinθ/r2 dB∝1/r2

#### A conducting wire carrying a current of 1A is placed vertically. The magnetic field in the direction of the length of the conductor due to a small current element of unit length is ____.

Correct! Wrong!

We know that, according to Biot-Savart law, dB= (μ0/4π) × idlsinθ/r2
When the point is considered in the direction of length of the conductor, θ=0o
When θ=0o, sin0o=0
Then the magnetic field at the point in the direction of current is Zero.

#### A moving coil galvanometer into an ammeter by connecting a ____.

Correct! Wrong!

A galvanometer can be converted into an ammeter by connected a small resistance in parallel, called shunt. Then it can be used to measure current.

#### Consider the following statements about the representation of the magnetic field Statement P: The magnetic field emerging out of the plane of the paper is denoted by a cross (⊗). Statement Q: The magnetic field going into the plane of the paper is denoted by a dot (⊙).

Correct! Wrong!

The magnetic field emerging out of the plane of the paper is denoted by a dot (⊙). The magnetic field going into the plane of the paper is denoted by a cross (⊗). Hence the statements P and Q are false.

#### Regarding the magnetic effects of electric current". Assertion (A): A negatively charged particle is projected near a current carrying conductor along the current direction, the negative charge moves away from the conductor. Reason (R): The current carrying conductor produces magnetic field and the moving charge also produces magnetic field.

Correct! Wrong!

The current carrying conductor produces magnetic field around it in the form of circular loops. When the projected charge is moving, the moving charges also produces magnetic field. These two magnetic fields interact each other and the electron moves away from the rod. Hence, Both Assertion and Reason are true, and the Reason is the correct explanation for Assertion.

#### If a conducting wire carries a direct current, the magnetic field associated with the current will be____.

Correct! Wrong!

When a conducting wire carries a current it produces magnetic field around it in the form of circular loops. It is completely outside the conductor. There is no magnetic field inside the conductor.

#### In mass spectrometer, the charged particles are separated based on their ____.

Correct! Wrong!

A mass spectrometer is used to separate the charged particles, when they are allowed to pass through combined electric field and magnetic field. These charged particles are separated based on their charge to mass ratio. The ratio of charge to mass is called specific charge.

#### The direction of magnetic field produced by long conductor is given by ____.

Correct! Wrong!

The direction of magnetic field produced by a long conductor can be find b y using right hand thumb rule. Imagine the conducting wire holding in your right hand with your extended thumb pointed in the direction of current. Then the direction of curl of the fingers represent the direction of magnetic field.

#### Charges at rest can produce ____.

Correct! Wrong!

Charges at rest can produce only electric field. The study of these static electric fields is known as electrostatics. Whereas the moving charges produces both electric field and magnetic field.

#### In a power line, a current is flowing along north direction. Then the direction of magnetic field above the power line is ____. (Neglect the Earth's magnetic field)

Correct! Wrong!

Imagine a power transmitting line, when the current direction is along the north, we get the direction of magnetic field by applying the right hand thumb rule. The direction of magnetic field is towards East.

#### An electron moving with a uniform velocity along positive Y-direction enters in a magnetic field directed along the positive X-axis. Then the force acting on the electron is directed along ____.

Correct! Wrong!

The force acting on a charged particle in a magnetic field is perpendicular to the direction of magnetic field and also perpendicular to the direction of motion. When the magnetic field is along positive X-direction the charged particle is moving along positive and the charged particle is moving along positive Y-direction, the force acting on the charged particle will be along the positive Z-direction. But, in this case, the charged particle is an electron. As the electron has negative charge, the force acting on the moving electron in the magnetic field is along negative Z-direction.

#### Which of the following particle will experience the maximum magnetic force when projected with same velocity perpendicular to a magnetic field?

Correct! Wrong!

The force acting on a charged particle projected perpendicular to the magnetic field is, F=Bqv When the velocity and magnetic field are same, F∝q Now compare the charge of given particles. Li+ has a charge of +2e. Proton and He+ have a charge of +e. Whereas the electron has a charge of−e. Thus, the ion Li+ experiences maximum force.

#### Consider the following statements about the electric field and magnetic field: Statement P: The magnetic field due to a current carrying wire does not depend on the angle. Statement Q: The electric field due to a charged particle is varies according to inverse square law.

Correct! Wrong!

For statement P, the magnetic field due to a current carrying wire depends on the angle between the length of the current element and the line joining the point and the current element. Hence, the statement P is false. For statement Q, the electric field due to a charged particle is varies according to inverse square law. That is, E∝1/r2 Hence the statement Q is true.

Class 12th Physics - 4 Moving charges and magnetism MCQs
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