Tag: magnetic fields and electromagnetism

Questions Related to magnetic fields and electromagnetism

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

Current in a circular coil having negligible resistance and inductance 0.1 H is increasing at the rate of $1 As^{-1}$. The power generated in the coil when the magnetic flux linked with it is 0.1 Wb will be:-

  1. 0.05 W

  2. 0.1W

  3. 1 W

  4. 10 W

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Induced EMF e = -L * (di/dt) = -0.1 * 1 = -0.1 V. Power P = e * i. The current i = flux / L = 0.1 / 0.1 = 1 A. P = 0.1 * 1 = 0.1 W.

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

The magnetic flux density at a point distant $d$ from a long straight current carrying conductor is $B$, then its value at distance $d/2$ will be:

  1. $4B$
  2. $2B$
  3. $B/2$
  4. $B/4$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Flux density, B $=\dfrac{\phi}{A}$
$B _A=\dfrac{\mu _0 I}{2\pi d}=B$
$=\dfrac{\phi}{A}$
$B _A=\dfrac{\mu _0 I}{2\pi \dfrac{d}{2}}=2\dfrac{\mu _0 I}{2\pi d}$
$B _B=2\times B$
$B _B=2B$

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

The magnetic needle of a tangent galvanometer is deflected at an angle $30$ due to a magnet. The horizontal component of earth's magnetic field $0.34\times 10^{-4}T$ is along the plane of the coil. The magnetic intensity is:

  1. $1.96\times 10^{-4}T$
  2. $1.96\times 10^{-5}T$
  3. $1.96\times 10^{4}T$
  4. $1.96\times 10^{5}T$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The correct option is B.


Given,

$B=0.34\times10^{-4}T$

Deflected angle$\theta=30^0$

So magnetic intensity is $Btan 30^0$

$=0.34\times10^{-4}T\times\dfrac{1}{\sqrt3}$

$=1.96\times10^{-5}T$

Where,$tan 30^0=\dfrac{1}{\sqrt3}$, and $\sqrt3=1.73$c

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

A sphere of radius $R$ and charge $Q$ is placed inside an imaginary sphere of radius $2R$. Whose center coincides with the given sphere. The flux related to the imaginary sphere is:

  1. $\dfrac {Q}{\in _{0}}$
  2. $\dfrac {Q}{2\in _{0}}$
  3. $\dfrac {4Q}{\in _{0}}$
  4. $\dfrac {2Q}{\in _{0}}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

According to Gauss's Law, the total electric flux through any closed surface is equal to the enclosed charge divided by epsilon_0. Since the inner sphere with charge Q is entirely enclosed by the imaginary sphere, the flux is Q/epsilon_0.

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

In a circuit a coil of resistance $2\,\Omega$, then magnetic flux charges from $2.0\,Wb$ to $10.0\,Wb$ in $0.2\ sec.$ The charge flow in the coil during this time is:

  1. $5.0\ C$
  2. $4.0\ C$
  3. $1.0\ C$
  4. $0.8\ C$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The relation between the rate of change of charge (or current) and the flux is given by the following relation:  

$ \because \dfrac{dQ}{dt}=-\dfrac{1}{R}\dfrac{d\phi }{dt} $

$ \dfrac{dQ}{dt}=\dfrac{-(10-2)}{2}=4\,C $


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

Two coils $A$ and $B$ are wound on the same iron  core as shown in figure. The number of turns in the coil $A$ and $B$ are $N _{A}$ and $N _{B}$ respectively. Identity the correct statement 

  1. Both the coils have same magnitude of magnetic flux

  2. The magnetic flux linked are in the ratio $\dfrac{\phi A}{\phi B}=\dfrac{N _{A}}{N _{B}}$
  3. The induced emf across each coil are in the ratio $\dfrac{E _{A}}{E _{B}}=\left(\dfrac{N _{4}}{N _{B}}\right)^{2}$
  4. Both the coils have same magnitude of induced emf

Reveal answer Fill a bubble to check yourself
B Correct answer