Tag: electromagnetic induction and alternating currents

Questions Related to electromagnetic induction and alternating currents

The inductance is measured in 

introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

  1. Ohm

  2. Farad

  3. henery

  4. None of these

Show answer
Correct Option: C

if the length and area of cross section of an inductor remain same but the number of turns is doubled its self inductance will become:

introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

  1. half

  2. four time

  3. double

  4. one- fourth

Show answer
Correct Option: B

The SI unit of inductance, the henry, can be written as :

introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

  1. weber / ampere

  2. volt second / ampere

  3. joule / ampere$^2$

  4. ohm second

Show answer
Correct Option: A,B,C,D
Explanation:

$ L\dfrac{dI}{dt} = emf = \dfrac{d\phi}{dt}$


a) $ [L] = weber / ampere $

b) $ [L] = volt.second / ampere $

c) $ Joule = volt \times ampere \times second $

$ \Rightarrow volt \times second = Joule / ampere$

$ \Rightarrow [L] = joule/ ampere^2$

d) $ V = IR \Rightarrow volt = ampere.ohm$

$\Rightarrow [L] = ohm.second$.

If a spark is produced on removing the load from an AC circuit then the element connected in the circuit is

introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

  1. high resistance

  2. high capacitance

  3. high inductance

  4. high impedance

Show answer
Correct Option: C
Explanation:

On removal of load from the circuit, the circuit suddenly becomes an open circuit.
Thus $ \dfrac{di}{dt} \rightarrow \infty $
For sparking, high voltage must appear across the open ends. This will happen only in case of an inductor as the voltage drop across the inductor is $ L\dfrac{di}{dt} $
Therefore, the circuit has high inductance.

If N is the number of turns in a coil, the value of self-inductance varies are

introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

  1. N$^o$

  2. N

  3. N$^2$

  4. N$^{-2}$

Show answer
Correct Option: C
Explanation:

Factual question, self inductance is proportional to square of the number of turns in coil.

Which of the following units denotes the dimensions ${M}{L}^{2}/{Q}^{2}$, where ${Q}$ denotes the electric charge?

introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

  1. $Weber$ ($Wb$)

  2. $Wb$$/\mathrm{m}^{2}$

  3. $Henry$ ($H$)

  4. $\mathrm{H}/\mathrm{m}^{2}$

Show answer
Correct Option: C
Explanation:

Weber $=ML^2T^{-2}I^{-1}$
$=ML^2T^{-2}Q^{-1}T=ML^2T^{-1}Q^{-1}$   ($I=QT^{-1}$)
Henry H is  SI unit of inductance. 
$H=ML^2T^{-2}I^{-2}$     also $I=QT^{-1}$
so $H=ML^2T^{-2}Q^{-2}T^2=ML^2Q^{-2}$

If $N$ is the number of turns in a circular coil then the value of self inductance varies as

introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

  1. ${N}^{0}$

  2. $N$

  3. ${N}^{2}$

  4. ${N}^{-2}$

Show answer
Correct Option: B
Explanation:

Self inductance depend on the number of turns in a coils $L \propto N$.

A magnetic field of $2\times {10}^{-2}T$ acts at right angles to a coil of area $100{cm}^{2}$ with $50$ turns. The average emf induced in the coil is $0.1V$. When it is removed from the field in $t$ second, the value of $t$ is

introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

  1. $10s$

  2. $0.1s$

  3. $0.01s$

  4. $1s$

Show answer
Correct Option: B
Explanation:

$e=\cfrac { -\left( { \phi  } _{ 2 }-{ \phi  } _{ 1 } \right)  }{ t } =\cfrac { -\left( 0-NBA \right)  }{ t } =\cfrac { NBA }{ t } $
$ \therefore \quad t=\cfrac { NBA }{ e } =\cfrac { 50\times 2\times { 10 }^{ -2 }\times { 10 }^{ -2 } }{ 0.1 } \quad t=0.1s$

The inductive reactance of a coil of $0.2H$ inductance at a frequency of $60Hz$ is:

introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

  1. $7.54\Omega $

  2. $0.754 \Omega $

  3. $75.4\Omega $

  4. $7.54\times { 10 }^{ -3 }\Omega $

Show answer
Correct Option: C
Explanation:

${ X } _{ L }=\omega L=2\pi fL$
$=2\times \cfrac { 22 }{ 7 } \times 60\times 0.2=75.4\Omega $

The SI unit of inductance, the henry, can be written as :

introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

  1. Weber ampere$^{-1}$

  2. Volt - s ampere$^{-1}$

  3. Joule ampere$^{-1}$

  4. ohm $s^{-1}$

Show answer
Correct Option: B
Explanation:

$V=L\dfrac{di}{dt}$

So the unit $L=\dfrac{Vdt}{di}$
so SI unit of L is $Volt-s\,ampere^{-1}$