Question 11 Mark
What is the effect of core on self-induction?
Answer
View full question & answer→Increases
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Question 21 Mark
Volt $-$ second is unit of which physical quantity?
Answer
View full question & answer→From $\varepsilon=\frac{\Delta \phi}{\Delta t }, \Delta \phi=\varepsilon \times \Delta t$
$ \text { Unit of magnetic flux }=\text { Unit of induced emf } \varepsilon \times \text { unit }\text {of time }$
$ \text { Unit of magnetic flux }=\text { Unit of induced emf } \varepsilon \times \text { unit }\text {of time }$
Question 31 Mark
Graph between magnetic flux $\phi$ and electric current $I$ for two inductors $A$ and $B$ is given in the figure. The magnitude of self-inductance will be more for whom?
Answer
View full question & answer→Since $\phi= LI \Rightarrow L =\phi / I$ and $\phi= LI \Rightarrow \phi \propto I$
Hence there is a linear graph between $\phi$ and $I$ and slope of $\phi / I$ will represent the self-inductance of the inductor. The slope of A is more than as compared to that of B , so selfinductance of A will be more.
Hence there is a linear graph between $\phi$ and $I$ and slope of $\phi / I$ will represent the self-inductance of the inductor. The slope of A is more than as compared to that of B , so selfinductance of A will be more.
Question 41 Mark
In the given figure, magnitude of current is increasing in the wire xy from x to y . Is there any induced current in a loop placed near the wire?
Answer
View full question & answer→Yes, and direction of induced current will be clockwise. According to right hand thumb rule, due to current in wire xy, magnetic field passing through the loop will be perpendicularly outwards and according to Lenz's law, the direction will be such that it opposes the current from increasing in that surface.
Question 51 Mark
What will be the magnitude of induced current in circular loop KLMN of radius $r$ if constant current of $1 A$ is passed in straight wire $P Q$ ?
Answer
View full question & answer→Zero, because when current is kept constant in PQ , then there is no change in magnetic flux in a coil placed near to it, hence no current will be induced.
Question 61 Mark
Two coils $P$ and $Q$ are shown in the figure given. What will be the direction of momentarily induced current in coil $Q$ when (i) switch $K$ is closed and (ii) switch $K$ is again opened after some time?
Answer
View full question & answer→(i) Anticlockwise (ii) Clockwise.
Question 71 Mark
When a current of 2 A is passed through a coil, then magnetic flux of magnitude 40 milli $W b$ is obtained. What is self-induction of the coil?
Answer
View full question & answer→$L=\frac{N \phi}{I}=\frac{40 \times 10^{-3} \text { Weber }}{2 \text { Ampere }} $
$=20 \times 10^{-3}$
$=20 \times 10^{-3}=20 mH$
$=20 \times 10^{-3}$
$=20 \times 10^{-3}=20 mH$
Question 81 Mark
Two coils one of larger radius $R$ and other of smaller radius $r$ are kept near. If mutual induction coefficient for this pair is $1 mH$ what is the magnetic flux associated with the larger coil when a current of $0.5 A$ is flowing in the smaller coil? When current in smaller coil is zero then what is its effect on larger coil?
Answer
View full question & answer→Given : $ M=1 m $ henry $=10^{-3} H$
$I_1=0.5 A $
$\therefore$ Magnetic flux related ot larger coil
$ \phi_2 =MI_1=10^{-3} \times 0.5$
$ =5.0 \times 10^{-4} Wb $
When current in the smaller coil becomes zero, then induced emf will be generated in larger coil due to decrease in magnetic flux.
$I_1=0.5 A $
$\therefore$ Magnetic flux related ot larger coil
$ \phi_2 =MI_1=10^{-3} \times 0.5$
$ =5.0 \times 10^{-4} Wb $
When current in the smaller coil becomes zero, then induced emf will be generated in larger coil due to decrease in magnetic flux.
Question 91 Mark
Current obtained from a choke coil of 2 henry is decreasing at the rate of $5 A / s$. Calculate the electromotive force developed across the ends of the coil.
Answer
View full question & answer→$\quad \frac{\Delta I }{\Delta t}=-5 A / s$ and $L =2 H$
$\varepsilon=- L \left(\frac{\Delta I }{\Delta t }\right)=-2 \times(-5)=10 volt$
$\varepsilon=- L \left(\frac{\Delta I }{\Delta t }\right)=-2 \times(-5)=10 volt$
Question 101 Mark
An emf of 20 m volt is induced in the coil when the rate of change of current in the solenoid is $4 A / s$, then what is the self-inductance of the coil?
Answer
View full question & answer→$|\varepsilon|= L \frac{\Delta I }{\Delta t } \Rightarrow L =\frac{|\varepsilon|}{\frac{\Delta I }{\Delta t }}$
$L =\frac{20 \times 10^{-3} \text { Volt }}{4 \text { Ampere } / \text { second }}$
$=5 \times 10^{-3} \frac{\text { Volt } / \text { second }}{\text { Ampere }}$
$=5 \times 10^{-3}$ Henry $=5 mH$
$L =\frac{20 \times 10^{-3} \text { Volt }}{4 \text { Ampere } / \text { second }}$
$=5 \times 10^{-3} \frac{\text { Volt } / \text { second }}{\text { Ampere }}$
$=5 \times 10^{-3}$ Henry $=5 mH$
Question 111 Mark
Write Faraday's laws of electromagnetic induction.
Answer
View full question & answer→Faraday gave two important laws on the phenomenon of electromagnetic induction
1. First law of Faraday: When magnetic flux linked with a coil changes then induced emf and induced current is generated in the coil. Induced emf is developed only till the change in the magnetic flux is taking place.
2. Second law of Faraday: According to this law, emf induced in the coil is proportional to the rate of change of flux.
1. First law of Faraday: When magnetic flux linked with a coil changes then induced emf and induced current is generated in the coil. Induced emf is developed only till the change in the magnetic flux is taking place.
2. Second law of Faraday: According to this law, emf induced in the coil is proportional to the rate of change of flux.
Question 121 Mark
Write the expression for self-inductance of any coil.
Answer
View full question & answer→$L=\frac{\mu_0 \pi N^2}{R}$ Henry.
Question 131 Mark
Is it possible for a man sitting in the train to measure induced emf generated in axis of train?
Answer
View full question & answer→No, because the train is stationary relative to man. Since v=0, so induced emf will also be zero.
Question 141 Mark
How two coils should be winded so that magnitude of induced electromotive force is maximum?
Answer
View full question & answer→One coil should be winded over the other coil because of which induced electromotive force will be maximum.
Question 151 Mark
Why self-induction is called inertia of electricity?
Answer
View full question & answer→Self-induction is that property of a coil by virtue of which it tries to maintain the magnetic flux associated with it which means it opposes any change in the flux. This property is similar to property of inertia in mechanics. Hence it is called inertia of electricity.
Question 161 Mark
In the figure given below, on moving a magnet NS kept between two coils AB and CD in the direction of arrow, in which coil the direction of induced current will be anticlockwise when seen from left?
Answer
View full question & answer→$AB \downarrow \uparrow$ anticlockwise.
Question 171 Mark
Write three factors on which the coefficient of self-induction of any coil depends.
Answer
View full question & answer→(i) Area of cross-section of the coil (ii) Number of turns in the coil and (iii) magnetic permeability of the core kept inside the coil
Question 181 Mark
If a core of iron is inserted in the middle of a coil, then what is the effect on the magnitude of its self- inductance?
Answer
View full question & answer→Magnitude of self-induction will increase
Question 191 Mark
Current in any circuit decreases from 5.0 A to 1.0 A in 0.1 s. If average induced emf is 200 V, then analyze self-induction in the coil.
Answer
View full question & answer→$I _1=5 A, I _2=0 A$
$d I = I _1- I _2=5-0=5 A$
$d t=0.1 s$
$e =200 Volt$
For self-inductance in the coil
$L =\frac{ e }{d I / d t}=\frac{200}{\frac{5}{0.1}}$
$L =\frac{ e }{d L / d t}=\frac{200}{\frac{5}{0.1}}$
$L =5 H$
$d I = I _1- I _2=5-0=5 A$
$d t=0.1 s$
$e =200 Volt$
For self-inductance in the coil
$L =\frac{ e }{d I / d t}=\frac{200}{\frac{5}{0.1}}$
$L =\frac{ e }{d L / d t}=\frac{200}{\frac{5}{0.1}}$
$L =5 H$
Question 201 Mark
If magnitude of current is made twice in any inductor, then how many times will the stored energy become?
Answer
View full question & answer→$U =\frac{1}{2} Lt _0^2$
On doubling the magnitude of current
$\therefore \quad U ^{\prime}=\frac{1}{2} L\left(2 I _0\right)^2=4 \times \frac{1}{2} LI _0^2$
$U ^{\prime}=4 U$
Hence, the stored energy will become four times.
On doubling the magnitude of current
$\therefore \quad U ^{\prime}=\frac{1}{2} L\left(2 I _0\right)^2=4 \times \frac{1}{2} LI _0^2$
$U ^{\prime}=4 U$
Hence, the stored energy will become four times.
Question 211 Mark
When the south pole of a bar magnet is taken close to a coil, then what is the direction of induced current in the coil? Explain with reason.
Answer
View full question & answer→Clockwise because due to this south pole will be formed at the ends of coil which according to Lenz's law will oppose the motion of the magnet towards it.
Question 221 Mark
In resistance box, the resistor wires that are used are joined by folding twice in the shape of the coil. Why?
Answer
View full question & answer→For the solution of self-inductance effect.
Question 231 Mark
In a rectangular wire, due to a source of emf, a constant current is flowing from left to right. When the switch of the source is off, then what will be the direction of induced current in the wire?
Answer
View full question & answer→From left to right (on switching off, the direction of induced emf is same in which the current was flowing).
Question 241 Mark
In two co-axial same circular coils, same current is flowing in the same direction. If both the coils are brought towards each other, then what will be the change in the current?
Answer
View full question & answer→Current will decrease in both the coils (by Lenz's law).
Question 251 Mark
Self-inductance of any coil is 1 H. What do you understand by this?
Answer
View full question & answer→$\varepsilon=- L \frac{d I }{d t}$
Here $L =1$, then $\quad \varepsilon=-\frac{d I }{d t}$
Which means that when rate of change of electric current is $1 A / s$, then emf of 1 volt will be induced.
Here $L =1$, then $\quad \varepsilon=-\frac{d I }{d t}$
Which means that when rate of change of electric current is $1 A / s$, then emf of 1 volt will be induced.
Question 261 Mark
How the direction of induced electromotive force is determined?
Answer
View full question & answer→By Lenz's law
Question 271 Mark
Lenz's law is based on conservation of which physical quantity?
Answer
View full question & answer→Energy conservation
Question 281 Mark
Is magnitude of induced electromotive force in any coil depends on resistance of the circuit?
Answer
View full question & answer→No (because magnitude of induced electromotive force depends only on the rate of change of magnetic flux)
Question 291 Mark
What is the form of stored energy in any coil?
Answer
View full question & answer→Magnetic energy
Question 301 Mark
If plane of any loop is kept parallel to the magnetic field, then what is the magnitude of magnetic flux associated with the loop?
Answer
View full question & answer→Zero, because $d \phi_A= B d A \cos 90^{\circ}=0$.
Question 311 Mark
On what factors does magnetic flux associated with a coil kept in any magnetic field depends?
Answer
View full question & answer→When a coil is kept in any external magnetic field, then magnetic flux associated with it depends on :
$ \because \phi_{B}=NBA \cos \theta $
(i) the area of the plane A of the coil.
(ii) intensity of magnetic field $B$.
(iii) angle $\theta$ made by the axis of coil with the direction of magnetic field.
(iv) number of turns N .
$ \because \phi_{B}=NBA \cos \theta $
(i) the area of the plane A of the coil.
(ii) intensity of magnetic field $B$.
(iii) angle $\theta$ made by the axis of coil with the direction of magnetic field.
(iv) number of turns N .
Question 321 Mark
On what factors is induced current in a coil depends?
Answer
View full question & answer→Induced current depends on: (i) Number of turns in the coil (ii) Resistance of the coil and (iii) Rate of change of flux in the coil.
Question 331 Mark
Write S.I. unit and dimension of magnetic flux.
Answer
View full question & answer→S.I. unit is weber and dimension is $\left[ ML ^2 T^{-2} A^{-1}\right]$.
Question 341 Mark
When magnetic flux passing through any coil changes, is (i) an induced electromotive force and (ii) current always generated?
Answer
View full question & answer→Induced electromotive force is always generated but induced current is generated only when the circuit of the coil is closed.
Question 351 Mark
Use Lenz's law to determine the direction of induced current in the situations described in the given figure:
(a) A wire of irregular shape turning into a circular shape.
(b) A circular loop being deformed into a narrow straight wire.
(a) A wire of irregular shape turning into a circular shape.
(b) A circular loop being deformed into a narrow straight wire.
Answer
View full question & answer→(a) Along the direction adcb, during shape change flux passing through the surface increases. Hence, induced current generates opposing flux.
(b) Along a'b'c'd' (flux decreases in this).
(b) Along a'b'c'd' (flux decreases in this).