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 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

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 $\overset{\rightarrow}{r}$.

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

Biot-Savart law indicates that the moving electrons (velocity $\bar v$ ) produce a magnetic field $\bar B$ such that:

  1. $\bar B \perp \bar v$
  2. $\bar B \parallel \bar v$

  3. it obeys inverse cube law.

  4. it is along the line joining the electron and point of observation.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Magnetic field produced by charges moving with velocity $\bar v$, at a distance r is $ \bar B$ = $\left ( \dfrac{\mu _0}{4\pi } \right )$.q$\dfrac{\bar v \times \hat r}{r^2}$
Therefore $\bar B \perp \bar v$

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

A vertical straight conductor carries a current vertically upwards. A point P lies to the east of it at a small distance and another point Q lies to the west at the same distance the magnetic field at P is :

  1. greater than at Q

  2. same as at Q

  3. less than at Q

  4. greater or less than at Q depending upon the strength of current
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

As per Biot Savart Law, Magnetic field at a point is inversely proportional to square of distance from the current carrying conductor. Therefore magnitude of magnetic field is same at both points P and Q, irrespective of their position from the conductor.

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

Which of the following particles will deviate $(< \pi/2)$ maximum when they enter magnetic filed region perpendicularly with same velocity and travel same distance.

  1. $He^{}$

  2. Proton
  3. $\alpha-particle$
  4. $Li^{++}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The radius of the path is r = mv / (qB). For the same velocity and distance, the particle with the smallest radius (highest q/m ratio) will deviate the most. Li++ has a higher charge-to-mass ratio than the others.

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

Which of the following gives the value of magnitude field according to, Biot-Savart's law'

  1. $ \frac {i\triangle l sin \theta}{r^2} $
  2. $ \frac {\mu _o}{4 \pi} \frac {i \triangle l sin \theta}{r} $
  3. $ \frac {\mu _o}{4\pi} \frac {i \triangle l sin \theta}{r^2} $
  4. $ \frac {\mu _o}{4 \pi} i \triangle l sin \theta $
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Biot-Savart's law states that the magnetic field dB is proportional to i*dl*sin(theta)/r^2. The constant of proportionality is mu0/4pi.