Physics

Magnetism and Magnetic Effects

230 Questions

Magnetism and magnetic effects focus on the forces exerted by magnetic fields on moving charges and magnetic materials. Questions cover magnetic dipoles, flux density, the motion of charged particles, and electromagnetic relationships. It is a vital physics topic for government competitive exams.

Magnetic dipolesCharged particle motionMagnetic flux densityBar magnetsEarth magnetism

Magnetism and Magnetic Effects Questions

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 positively charged particle falls vertically downwards. The horizontal component of earths magnetic field will deflect it towards

  1. West

  2. East

  3. South

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

Using Fleming's left-hand rule, the force on a positive charge is F = q(v x B). With velocity downwards and the horizontal magnetic field component pointing North, the cross product results in a force directed towards the East.

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 electron is travelling along the x-direction. It encounters a magnetic field in the ydirection. Its subsequent motion will be

  1. straight line along the x-direction

  2. a circle in the zx-plane

  3. a circle in the yz-plane

  4. a circle in the xy-plane
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The magnetic force acting on a charged particle is given by 

$\vec{F}=q(\vec{v}\times \vec{B})$
Hence direction of force acting one electron is $\hat{i}\times \hat{j}=\hat{k}$
The force experienced is in z-direction. So the particle moves in the zx plane.

Multiple choice physics magnetic fields and electromagnetism fleming's left hand rule magnetic force magnetic force on a moving charge and current carrying wire

An electron is moving vertically downwards at any place. The direction of magnetic force acting on it due to horizontal component of earth's magnetic field will be

  1. towards east

  2. towards west

  3. towards north

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

According to Fleming left hand rule, if the direction of horizontal component of earth's magnetic field is from south to north and direction of velocity of electron is downwards then the direction of the force given by the thumb is towards west.

Multiple choice physics magnetic fields and electromagnetism fleming's left hand rule magnetic force magnetic force on a moving charge and current carrying wire

An electron and a proton travel with equal speeds and in the same direction, at $90^o$ to a uniform magnetic field. They experience forces which are initially

  1. in opposite direction and differ by a factor of about 1840

  2. in the same direction and differ by a factor of about 1840

  3. equal in magnitude but in opposite directions

  4. identical
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
As both of the particle having same speed and in the same field at same angle, they will be experiencing same force but in opposite direction as they are opposite in charge. 
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 proton is projected horizontally eastward in a uniform magnetic field, which is horizontal and southward in direction. The proton will be deflected

  1. upward

  2. downward

  3. northward

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

By Fleming's left hand rule, taking velocity (middle finger) in east direction and magnetic field (index finger) in south direction, we get force (thumb) in vertically downward direction.

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 electron enters a magnetic field at right angles to it. The direction of force acting on the electron will be

  1. to the right.

  2. to the left.

  3. out of the page.

  4. into the page.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Using the right-hand rule for a negative charge (electron), the force is opposite to the direction determined for a positive charge. If the electron enters perpendicular to the field, the force is directed into the page.

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 electron is moving towards east in a magnetic field acting vertically downwards. So the electron is deflected towards:

  1. South

  2. North

  3. East

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

An electron is moving towards east in a magnetic field acting vertically downwards. So, the electron is deflected in a mutually perpendicular direction to magnetic field. Using Fleming's left hand rule it is in south direction .

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

At an instant a charge q moves with a velocity of 5 m/s along y-axis in a uniform magnetic filed $\underset{B}{\rightarrow}=(2\widehat{i}+3\widehat{j}+4\widehat{k})$

  1. The charge will experience a force in xy plane

  2. The charge will experience a force in yz plane

  3. The charge will experience a force in zx plane

  4. The charge will experience a force along x-axis
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The force F = q(v x B). Given velocity v = 5j and B = 2i + 3j + 4k, the cross product v x B = 5j x (2i + 3j + 4k) = 10(j x i) + 15(j x j) + 20(j x k) = -10k + 0 + 20i. The resulting vector (20i - 10k) lies in the zx plane.

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 charge particle is moving in the direction of a magnetic filed.The magnetic force acting on the particle:

  1. is in the direction of its velocity

  2. is in the direction opposite to its velocity

  3. is perpendicular to its velocity

  4. is zero
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The magnetic force on a moving charge is F = q(v x B). If the charge moves parallel to the magnetic field, the angle between v and B is 0 degrees, so the cross product (and thus the force) is zero.

Multiple choice physics magnetism and matter paramagnetic material classification of magnetic material magnetism

The magnetic susceptibility of a paramagnetic material at $-73^0$ is $0.0075$, its value at $-173^0$C will be

  1. $0.0045$
  2. $0.0030$
  3. $0.015$
  4. $0.0075$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Given,
$X=0.0075 \,\,at\,\,\, T=-73^{\circ}$
Curie's law, $X=\cfrac{C}{T}$
$X _{1} \propto \cfrac{1}{T _{1}}$
$\therefore \cfrac{X _{1}}{X _{2}}=\cfrac{T _{2}}{T _{1}}$
$X _{2}=X _{1}\times \cfrac{T _{1}}{T _{2}}=0.0075\times \cfrac{273-73}{2.73-173}=0.015$

Multiple choice physics electromagnetic forces magnetic field due to a circular current carrying conductor magnetic field produced in a circular loop oersted experiment oersted's experiment magnetic field due to a straight current carrying conductor

Consider a region where both uniform electric and magnetic fields E and B are present both along the z-axis. A positively charged particle of charge and mass is released from the origin with an initial velocity ${{\text{V}} _e}\hat i$. Which of the following option(s) are correct?

  1. (A)The y coordinate of the particle at time ${\text{t}} = \frac{{\pi {\text{M}}}}{{{\text{qB}}}}{\text{ is}}\frac{{ - 2{\text{mv}}}}{{{\text{qB}}}}$

  2. (B)The distance between two consecutive point on the z-axis where the particle touches the Z-axis is an odd multiple of a constant distance.

  3. (C)The distance between two consecutive point on the z-axis where the particle touches the Z-axis is an even multiple of a constant distance.
  4. (D)The time after which the particle touches the z-axis is $\frac{{2\pi {\text{m}}}}{{{\text{qB}}}}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

This is a classic problem of a charged particle in crossed electric and magnetic fields. The particle undergoes cycloidal motion. The y-coordinate calculation at the specified time is a standard derivation for this motion.

Multiple choice motion of charged particle in magnetic field and electric field moving charges and magnetism magnetic effects of current and magnetism physics

Two particles X and Y having equal charges, after being accelerated through the same potential difference, enter a region of uniform magnetic field and describe circular paths of radii $R _{1}$ and $R _{2}$ respectively. The ratio of masses of X and Y is-

  1. $(R _{1}/R _{2})^{1/2}$
  2. $(R _{2}/R _{1})$
  3. $(R _{1}/R _{2})^{2}$
  4. $(R _{1}/R _{2})$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The radius of a charged particle in a magnetic field is R = sqrt(2mK)/qB, where K is kinetic energy. Since the particles are accelerated through the same potential difference V, K = qV. Substituting this, R = sqrt(2mV)/B. Thus, R is proportional to sqrt(m), meaning R^2 is proportional to m. Therefore, m1/m2 = (R1/R2)^2.

Multiple choice motion of charged particle in magnetic field and electric field moving charges and magnetism magnetic effects of current and magnetism physics

An electron and a proton are injected into a uniform magnetic field perpendicular to it in the same direction. If electron and proton have same kinetic energy then the radius of curvature is 

  1. more for proton

  2. more for electron

  3. same for both

  4. none of thesr
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

let, Kinetic energies of electron and proton be K.
magnetic force on particle provides the centripetal force to support the circular motion.
If r is radius of curvature, $ F _b = F _c $
i.e. qvB = m $\frac{v^2}{r} $.
Solving the above equation we get r = $ \frac {p}{qB} $ where p = momentum = mv
If, q and B are constant we can say that $ r \alpha p $
But, K.E. = $ \frac {mv^2}{2}$.
Derive P in terms of K.E. which turns out to be
p = ${(2m(K.E.))}^{\frac{1}{2}}$
Given that, K.E. is same for either particles. So, $p  \ \alpha \  m^{\frac{1}{2}}$
therefore, $ r \  \alpha \  p \  \alpha \  m^{\frac{1}{2}}$ and radius is more for higher mass particle which is a proton in this case.

Multiple choice motion of charged particle in magnetic field and electric field moving charges and magnetism magnetic effects of current and magnetism physics

An electron and a proton are injected into a uniform magnetic field perpendicular to it with the same momentum. If both particles are fired with same momentum into a transverse electric field, then

  1. electron trajectory is less curved

  2. proton trajectory is less curved

  3. both trajctories are equally curved

  4. both trajectories are straight lines
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

let, momentum of electron and proton be p.
Transverse electric force on particle provides the centripetal force to support the circular motion.
If r is radius of curvature, $ F _e = F _c $


i.e. $qE = m \dfrac{v^2}{r} $.

Solving the above equation we get r = $ \dfrac {p^2}{mqE} $ 

where, $p = momentum = mv$

Given $q$ ,$p$ and $E$ are constant. So, we can say that $ r \propto \dfrac{1}{m} $

Radius of curvature is higher for a lighter mass particle which is an electron and vice versa for proton.

Multiple choice motion of charged particle in magnetic field and electric field moving charges and magnetism magnetic effects of current and magnetism physics

An electron and a proton are injected into a uniform magnetic field perpendicular to it with the same momentum. If the two particles are injected into a uniform transverse electric field with same kinetic energy, then

  1. electron trajectory is more curved

  2. proton trajectory is more curved

  3. both trajectories are equally curved

  4. both trajectories are straight lines
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let, Kinetic energies of electron and proton be K.
Transverse electric force on particle provides the centripetal force to support the circular motion in this case.
If r is radius of curvature, $ F _e = F _c $


i.e. qE = m $\dfrac{v^2}{r} $.

Solving the above equation we get r = $ \dfrac {2K}{qE} $ where K = Kinetic Energy = $\dfrac {mv^2}{2}$


Here, q,E and K are constant. So, radius of curvature is same for both of them.