Tag: magnetic effects of current and magnetism

Quizzes (16) Questions (174)

Questions Related to magnetic effects of current and magnetism

Multiple choice physics magnetic effects of current and magnetism the bar magnet magnetic field due to bar magnet intensity of magnetic field and torque on a bar magnet

A charge particle moves in a uniform magnetic field. The velocity of the particle at some instant makes right angle with the magnetic field. The path of the particle will be

  1. A straight line

  2. A circle

  3. Any curved path

  4. Zig-zag
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When a charged particle enters a uniform magnetic field with a velocity perpendicular to the field, the magnetic force acts as a centripetal force, causing the particle to move in a circular path.

Multiple choice physics magnetic effects of current and magnetism the bar magnet magnetic field due to bar magnet intensity of magnetic field and torque on a bar magnet

A magnet is kept fixed with its length parallel to the magnetic meridian. An identical magnet is parallel to this such that its center lies on perpendicular bisector of both. If the second magnet is free to move, it will have

  1. translatory motion only

  2. rotational motion only

  3. both translatory and rotational motion

  4. vibrational motion only
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Both translatory and rotational motion as it will exprrience both torque and force.

Multiple choice physics magnetic effects of current and magnetism the bar magnet magnetic field due to bar magnet intensity of magnetic field and torque on a bar magnet

A current carrying wire is arranged at any angle in an uniform magnetic field, then

  1. only force acts on wire

  2. only torque acts on wire

  3. both

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

A current-carrying wire in a magnetic field experiences a Lorentz force given by F = I(L x B). Torque is only experienced if the wire is part of a loop or has a specific geometry allowing for a moment arm relative to an axis, but a simple wire experiences a net force.

Multiple choice physics magnetic effects of current and magnetism the bar magnet magnetic field due to bar magnet intensity of magnetic field and torque on a bar magnet

An infinitely long cylinder is kept parallel to an uniform magnetic field B directed along positive z axis. The direction of induced current as seen from the z axis will be 

  1. clockwise of the +ve z axis

  2. anticlockwise of the + ve z axis

  3. zero

  4. along the magnetic field
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Since the cylinder is parallel to the uniform magnetic field, the magnetic flux through any cross-section perpendicular to the z-axis remains constant. According to Faraday's law, no change in flux means no induced EMF and thus no induced current.

Multiple choice physics magnetic effects of current and magnetism the bar magnet magnetic field due to bar magnet intensity of magnetic field and torque on a bar magnet

When a charged particle moves perpendicular to a uniform magnetic field, its 

  1. energy and momentum both change.

  2. energy changes but momentum remains unchanged.

  3. momentum changes but energy remains unchanged.

  4. energy and momentum both do not change.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Since the force exerted by the magnetic field is perpendicular to the direction of the particle the speed of the particle cannot change but its velocity changes .

so C option is the correct answer

Multiple choice physics magnetic effects of current and magnetism the bar magnet magnetic field due to bar magnet intensity of magnetic field and torque on a bar magnet

A proton with kinetic energy K describes a circle of radius r in a uniform magnetic. An $\alpha$- particle with kinetic energy K moving in the same magnetic field will describe a circle of radius? 

  1. $\cfrac {r} {2}$

  2. r
  3. $2r$
  4. $4r$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

WE KNOW THAT 


charge on proton = q
charge on alpha particle = 2q

mass of proton =m 
mass of alpha particle =4m

for proton

 $ r =\dfrac{m\times v}{q\times B}$


for alpha particle

$ R = \dfrac{{4m}\times v}{2q\times B}$

$ R = \dfrac{2m\times v}{q\times B}$

$ R = 2r$

Multiple choice physics magnetic effects of current and magnetism the bar magnet magnetic field due to bar magnet intensity of magnetic field and torque on a bar magnet

A magnetic needle is placed parallel to a magnetic field. The amount of work done in rotating the coil by an angle of 60$^0$ is W units. Then, the torque required to keep the needle in the displaced position is

  1. W
  2. $\sqrt{3}$W
  3. $\left( \sqrt{3} / 2 \right )$W

  4. W/2
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Torque at an angle $\theta  = k sin \theta $


work done to bring from zero to 60 degree $ =W = \int _0^{60}{ k sin \theta d \theta } = {\left | -k cos \theta \right |} _0^{60} = \dfrac{k}{2} $

$ \Rightarrow k = 2W $

torque at 60 degree required to keep the needle stable  $= k sin 60 = 2 W \dfrac{\sqrt 3 }{2} = \sqrt 3 W $ 

Multiple choice physics magnetic effects of current and magnetism the bar magnet magnetic field due to bar magnet intensity of magnetic field and torque on a bar magnet

A bar magnet of moment $4Am^{2}$ is placed in a non-uniform magnetic field. If the field strength at poles are 0.2 T and 0.22 T then the maximum couple acting on it is

  1. 0.04Nm

  2. 0.84Nm

  3. 0.4 Nm

  4. 0.44Nm
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Average of the two field strengths at the poles is $\frac{0.2 +0.22}{2}=0.21$
Copuling( torque): $MB=4 \times 0.21 : Nm= 0.84:Nm$

Multiple choice physics magnetic effects of current and magnetism the bar magnet magnetic field due to bar magnet intensity of magnetic field and torque on a bar magnet

A magnet of length $30\ cm$ with pole strength $10\ A-m$ is freely suspended in a uniform horizontal magnetic field of induction $40 \times 10^{-6} T$ . If the magnet is deflected by $60^{o}$ from its equilibrium position, the restoring couple acting on it is :

  1. $10.39\times 10^{-5}\ Nm$
  2. $\sqrt{3} \times 10^{-5}Nm$
  3. $6\times 10^{-5} Nm$
  4. $\sqrt{5}\times 10^{-5}Nm$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$l=30\ cm$
$P=10\ Am$
$B=40\times 10^{-6}$
$\theta =60^o$
$m=pl$
$\vec{\tau}=\vec{m}\times \vec{B}$
$=mB\sin\theta $
$=10^{-6}\times \dfrac{\sqrt{3}}{2}$
$=1.039\times 10^{-4}Nm$
$=10.39\times 10^{-5}Nm$

Multiple choice physics magnetic effects of current and magnetism the bar magnet magnetic field due to bar magnet intensity of magnetic field and torque on a bar magnet

A current carrying ring with it center at origin and moment of inertia $1\times 10^{-2} kg-m^{2}$, about an axis passing through its center and perpendicular to its plane, has magnetic moment $\vec {M} = (3\hat {i} - 4\hat {j})A - m^{2}$, at time $t = 0$, a magnetic field $\vec {B} = (4\hat {i} + 3\hat {j})T$ is switched on. Maximum angular velocity of the ring is rad/sec will be

  1. $50\sqrt {2}$
  2. $100$
  3. $100\sqrt {2}$
  4. $150\sqrt {2}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The potential energy of a magnetic dipole in a field is U = -M dot B. The change in potential energy is converted into rotational kinetic energy (1/2)I(omega^2). Here, M dot B = (3)(4) + (-4)(3) = 0. However, the system starts from rest and the magnetic torque will cause rotation. The maximum angular velocity occurs when the potential energy is minimized (M aligned with B). The change in potential energy is delta U = M*B - M dot B = |M||B| - 0 = 5*5 = 25 J. Setting (1/2)I(omega^2) = 25 with I = 0.01 gives omega = sqrt(50/0.01) = sqrt(5000) = 50*sqrt(2).