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Questions Related to physics

Multiple choice introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

the number of turn of primary and secondary coil of the transformer is 5 and 10 respectively ad the mutual inductance is 25 H. if the number f turns of the primary and secondary is made 10 and 5 , then the mutual inductance of the coils will be

  1. 6.25 H

  2. 12.5 H

  3. 25 H

  4. 50 H
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$M=\mu _o\mu _r \cfrac {N _1N _2}{l}A$

$M \propto N _1N _2$
Since $N _1N _2=10 \times 5= 5 \times 10=50$ in both cases.
Mutual inductance will remain same.

Multiple choice introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

The coefficients of self induction of two inductance coils arc 0.0 1H and 0.03H respectively. When they are connected in series so as to support each other. then the resultant self inductance becomes 0.06 Henry. The value of coefficient of mutual induction will be-

  1. 0.02 H

  2. 0.05 H

  3. 0.01 H

  4. ZERO
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$L1=0.01$

$L2=0.03$
$L eff =0.06$

$Leff = L1+L2+2M$
$0.06=0.01+0.03+2M$
$2M = 0.06-0.03$
$M=0.03/2$
$=0.015$

Multiple choice introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

In an induction coil, the coefficient of mutual induction is 4 henry. If a current of 5 ampere in 1  the primary coil is cut off in $\frac { 1 }{ 1500 } $s, the e.m.f at the terminals of the secondary coil will be:

  1. 15 kV

  2. 60 kV

  3. 10 kV

  4. 30 kV
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

${\phi _{21}} = M.i,$

$ \Rightarrow v = \frac{{d{\phi _{21}}}}{{dt}} = M\frac{{di}}{{dt}}$
$ = 4 \times \frac{5}{{\left( {1/1500} \right)}}$
$ = 20 \times 1500$
$ = 30kv$
Hence,
option $(D)$ is correct answer.

Multiple choice introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

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:

  1. half

  2. four time

  3. double

  4. one- fourth
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Self-inductance L is proportional to the square of the total number of turns (N^2). If N is doubled, L becomes 2^2 = 4 times the original.

Multiple choice introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

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

  1. weber / ampere

  2. volt second / ampere
  3. joule / ampere$^2$

  4. ohm second
Reveal answer Fill a bubble to check yourself
A,B,C,D Correct answer
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$

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

Multiple choice introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

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

  1. high resistance

  2. high capacitance

  3. high inductance

  4. high impedance
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

Multiple choice introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

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

  1. $Weber$ ($Wb$)
  2. $Wb$$/\mathrm{m}^{2}$
  3. $Henry$ ($H$)
  4. $\mathrm{H}/\mathrm{m}^{2}$
Reveal answer Fill a bubble to check yourself
C Correct answer
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 $H=ML^2T^{-2}Q^{-2}T^2=ML^2Q^{-2}$