Physics

Magnetism and Magnetic Effects

218 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 option a: relativity the nature of light speed of light and optical density introduction to light

An electromagnetic wave is propagating along x-axis. At x = 1 m and t = 10 s, its electric vector |$\overset{-}{E}|  = 6 V/m$ then the magnitude of its magnetic vector is:

  1. $2 \, \times \, 10^{-8} \, T$
  2. $3 \, \times \, 10^{-7} \, T$
  3. $6 \, \times \, 10^{-8} \, T$
  4. $5 \, \times \, 10^{-7} \, T$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Electric and magnetic compounds of an electromagnetic field are related by 

$E = CB$
$B = \dfrac{E}{C}$
$B = \dfrac{6}{3 \times 10^8}$  (when $E$ is given)
$B = 2 \times 10^{-8} T$ 

Multiple choice the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

A plane electromagnetic wave travels in free space along X-direction. If the value of $\overrightarrow { B } $ (in tesla) at a particular point in space and time is $1.2 \times {10}^{-8} \hat {k}$, the value of $\overrightarrow { E } $ (in V ${m}^{-1}$) at that point is,

  1. $1.2\ \hat {j}$
  2. $3.6\ \hat {k}$
  3. $1.2\ \hat {k}$
  4. $3.6\ \hat {j}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Given: The magnetic field of the plane electromagnetic wave is $1.2×10^{-8} \hat k\ T$
The direction of propagation of the electromagnetic wave is along X-direction.

The magnitude of  $\vec E$ is given by:
$E\, = \, B\cdot c\\ \ \ \ \ = (1.2 \, \times \, 10^{-8} T)(3 \, \times \, 10^{-8} m \,  s^{-1})\\ \ \ \ \ = 3.6 \,  V/m$

Since the magnetic field is along $Z-$ direction and the wave propagates along $X -$ direction. Therefore $\vec E$  should be in a direction perpendicular to both $X$ and $Z$ axes.

Using vector algebra  should be along X-direction.

Since $(+\hat j) \times (\hat k )= \hat i$

$\vec E$ is along the $Y-$direction.
Thus,  $\vec E= 3.6\hat j\ Vm^{-1}$

Multiple choice physics dynamics - explaining motion system of unit summary of si units system of units

The magnetic field flux is expressed in

  1. Dynes

  2. Oersted

  3. Gauss

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

Magnetic Flux is defined as the number of magnetic field lines passing through a given closed surface. It gives the measurement of the total magnetic field that passes through a given surface area. S.I. unit of magnetic flux is Weber $(Wb)$.

Multiple choice physics magnetic fields and electromagnetism magnetic flux density magnetic flux electromagnetic induction

A cyclotron in which protons are accelerated has a flux density 1.57T. The variation of frequency of electric field is (in Hz) 

  1. $4.8 \times 10 ^ { 8 }$
  2. $8.4 \times 10 ^ { 8 }$
  3. $2.5 \times 10 ^ { 7 }$
  4. $4.8 \times 10 ^ { 6 }$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Cyclotron frequency f = qB / (2 * pi * m). For protons, q = 1.6e-19 C, m = 1.67e-27 kg, B = 1.57 T. f = (1.6e-19 * 1.57) / (2 * 3.14 * 1.67e-27) approx 2.4e7 Hz.

Multiple choice physics magnetic fields and electromagnetism magnetic flux density magnetic flux electromagnetic induction

In an experiment to measure the velocity of electrons, an electric field $(E)$ and a magnetic field $(B)$ are employed to produce zero deflection. Then :

  1. The two fields are parallel and the velocity is given by $BE$
  2. The two fields are perpendicular and the velocity is given by $E/B$
  3. The two fields are parallel and the velocity is given by $E/B$
  4. The two fields are perpendicular and the velocity is given by $BE$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The electric force on electron of charge ${e}$  is,
             $  F= {e}E $ 
                    where, E = electric field.

And Magnetic force ,
            $ F= {e}$ $(V\times B)$
               where, V= velocity of electron in magnetic field
                            B= magnetic field

From the above equations,

          $E= V\times B$
Electric field E is perpendicular to both velocity of electron and the magnetic field. So,  The two field is perpendicular to each other and the velocity of electron is $\dfrac{E}{B}$.

B. The two fields are perpendicular and the velocity is given by $\dfrac{E}{B}$.

Multiple choice physics oscillations introduction to sound free, forced and damped oscillations resonance

A bar magnet oscillates with a frequency of$ 10 $ oscillations per minute. When another bar magnet is placed on its axis at a small distance, it oscillates at $14$ oscillations per minute. Now, the second bar magnet is turned so that poles are instantaneous, keeping the location same. The new frequency of oscillation will be 

  1. $2$ vibrations/min
  2. $4$ vibrations/min
  3. $10$ vibrations/min
  4. $14$ vibrations/min
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$\dfrac{60}{10}= 2\pi \sqrt{\dfrac{l}{MB _H}}$
$\dfrac{60}{14}= 2\pi \sqrt{\dfrac{l}{M(MB _H)}}$
$\therefore \dfrac{7}{5} = \sqrt{B _H +B}{B _H} $ or $ B= \dfrac{24}{25}B _H$
Hence,
$\dfrac{60}{10}= 2\pi \sqrt{\dfrac{l}{M(B _H-B)}}= 2\pi \sqrt{\dfrac{l}{MB(1-24/25)}}$
$= 5\times 2\pi \sqrt{\dfrac{l}{2MB}} = 5 \times \dfrac{60}{10}= 30$
$\therefore f= \dfrac{60}{30} = 2$ vibrations/ min

Multiple choice physics nuclei nuclear force the nuclear force nuclear force and binding energy

Protons are placed in a magnetic field in a $Z$ direction (magnitude = 2.3 T). The energy difference between a state with $Z$ component of proton spin angular momentum parallel to the field and antiparallel to the field is 

  1. $4.05\times10^{7} eV$
  2. $4.05\times10^{-7} eV$
  3. $2.025\times10^{7} eV$
  4. $2.025\times10^{-7} eV$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$U _{1}$ = $|S _{z}|$ $B$
=$-2.7928\times(2.3T)\times 3.152\times10^{-8}\left(\displaystyle\ \frac{eV}{T} \right)$
= $-2.025\times10^{-7} eV$ (When $B$ and $|S _{z}|$ are parallel
$U _{2}$ = $+2.025\times10^{-7} eV$ when $B$ and $|S _{z}|$ are antiparallel.
$\therefore$ $\triangle U$ = $U _{2}$ -$U _{1}$ = $4.05\times10^{-7} eV$

Multiple choice electrostatic and magnetic analogy magnetism and matter magnetic effects of current and magnetism physics

Two equal poles repel each other with a force of 10$^{-3}$ N. When placed 2cm apart in air, the pole strength of each is (in amp-m).

  1. 4$\pi $

  2. 2

  3. 4
  4. 2$\pi $
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$F=10^{-3}N$
$d=2cm$
$m _{1}=m _{2}=m$
$F=\dfrac{\mu _{0}m _{1}m _{2}}{4\pi d^{2}}$

$10^{-3} = \dfrac{10^{-7}\times m^{2}}{(2\times 10^{-2})^2}$
$m=2Am$

Multiple choice electrostatic and magnetic analogy magnetism and matter magnetic effects of current and magnetism physics

The magnetic induction at a distance d from the magnetic pole of the unknown strength m is B. If an identical pole is now placed at a distance of 2d from the first pole, the force between the two poles is          

  1. mB
  2. $\frac{mB}{2}$
  3. $\frac{mB}{4}$

  4. 2mB
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
$B=\dfrac{\mu _{0}m}{4\pi d^{2}}$
$r=2d$
$F=\dfrac{\mu _{0}m _{1}m _{2}}{4\pi r^{2}}$
$F=\dfrac{\mu _{0}\times m\times m}{4\pi (d)^{2}}$
$F=\dfrac{\mu _{0}m^{2}}{4\pi \times 4d^{2}}$
$F=\dfrac{mB}{4}N$

Multiple choice electrostatic and magnetic analogy magnetism and matter magnetic effects of current and magnetism physics

Two magnetic poles have their strengths in the ratio 3 : 2. They are kept at a distance of 0.6 m in air and the force of repulsion is found to be 0.06 dynes. The pole strengths are (in amp. m)

  1. 1.8, 1.2

  2. 18, 12

  3. 6, 4

  4. 0.6, 3.6
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$1 dyne = 10^{-5}$
$\mu _{0}=4\pi \times 10^{-7}TmA^{-1}$ 
$m _{1}=3m$
$m _{2}=3m$
$F=\dfrac{\mu _{0}m _{1}\times m _{2}}{4\pi \times r^{2}}$ r=0.6m
$0.06\times 10^{-5}=\dfrac{4\pi \times 10^{-7}\times 3m\times 2m}{4\pi \times (0.6)^{2}}$
$m^{2}=(0.6)^{2}$
$m=0.6$
$m _{1}=1.8$
$m _{2}=1.2$




Multiple choice physics moving charges and magnetism field due to a current carrying conductor magnetic field due to a straight current carrying conductor magnetic field lines due to current

If an electron is moving with velocity $\bar{v}$ produces a magnetic field $\bar{B}$, then

  1. the direction of field $\bar{B}$ will be same as the direction of velocity $\bar{v}$
  2. the direction of field $\bar{B}$ will be opposite as the direction of velocity $\bar{v}$
  3. the direction of field $\bar{B}$ will be perpendicular as the direction of velocity $\bar{v}$
  4. the direction of field $\bar{B}$ does not depend upon the direction of velocity $\bar{v}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

According to Biot-Savart's law, the magnetic field
$\displaystyle \overset{\rightarrow}{B} = \frac{\mu _o}{4 \pi} . \frac{q (\overset{\rightarrow}{v} \times \overset{\rightarrow}{r} ) }{r^3}$
The direction of $\overset{\rightarrow}{B}$ will be along $\overset{\rightarrow}{v} \times \overset{\rightarrow}{r}$ i.e. perpendicular to the plane containing $\overset{\rightarrow}{v}$ and $\overset{\rightarrow}{r}$.