Self Induction

Q.

A long solenoid has $1000turns$. When a current of $4A$ flows through it, the magnetic flux linked with each turn of the solenoid is $4\times {10}^{-3}Wb$. What is the self-inductance of the solenoid?

Q. An inductor 20mH a capacitor 50microF and a resistor 40 ohm r connected in series across a source of emf V=10sin340t . The power loss in the circuit

Q.

A filament bulb (500w , 100 v) is to be used in 230v main supply . When resistance R is connected in series , it works perfectly and the bulb consumes 500w . The value of R is.

Q. An infinitely long line of charge of linear charge density$\lambda .$ The potential difference between two points $\text{A}$ and $\text{B}$ as shown in figure is –

1. $\frac{\lambda }{2\pi {\epsilon }_0}\ln 2$
2. $-\frac{\lambda }{2\pi {\epsilon }_0}\ln 2$
3. $\frac{\lambda }{4\pi {\epsilon }_0}\ln 2$
4. $-\frac{\lambda }{4\pi {\epsilon }_0}\ln 2$

Q. 106.Two electric bulbs whose resistances are in the ratio of 1:2 are connected in series to a constant voltage source. The power dissipated in them are in the ratio

Q.

What is the working principle of transformer?

Q. From Ampere’s circuital law for a long straight wire of circular cross-section carrying a steady current, the variation of magnetic field in the inside and outside region of the wire is

1. A linearly decreasing function of distance upto the boundary of the wire and then a linearly increasing one for the outside region.
2. Uniform the remains constant for both the regions.
3. A linearly increasing function of distance $r$ upto the boundary of the wire and then decreasing one with $\frac{1}{r}$ dependence for the outside region.
4. A linearly increasing function of distance upto the boundary of the wire and then linearly decreasing for the outside region.

Q.

The phase difference between current and voltage in an AC circuit is $\frac{\mathrm{\pi }}{4}\mathrm{radian}$. If the frequency of AC is $50\mathrm{Hz}$, then the phase difference is equivalent to the time difference of how many seconds?

Q. A coaxial cable consists of an inner wire of radius $a$ surrounded by an outer shell of inner and outer radii $b$ and $c$ respectively. The inner wire carries an electric current $i_0$, which is distributed uniformly across cross-sectional area. The outer shell carries an equal current in opposite direction and distributed uniformly. What will be the ratio of the magnetic field at a distance $x$ from the axis when (i) $x<a$ and (ii) $a<x<b$ ?

1. $\frac{b^2-a^2}{x^2}$
2. $\frac{x^2}{b^2-a^2}$
3. $\frac{a^2}{x^2}$
4. $\frac{x^2}{a^2}$

Q.

A solenoid 4cm in diameter and 20 cm in length has 250 turns and carries a current of 15A. Calculate the flux through the surface of a disc of 10 cm radius that is positioned perpendicular to and centered on the axis of the solenoid.

Q. A long cylindrical conductor of radius $R$ carries current $i$ as shown below. The current density $J$ is a function of radius $r$ as $J=br$ where $b$ is a constant. The magnetic field at a distance $r_1(r_1<R)$ is:

1. $\frac{{\mu }_{0}b{r}_1^2}{2}$
2. $\frac{{\mu }_{0}b{r}_1^3}{2}$
3. $\frac{{\mu }_{0}b{r}_1^2}{3}$
4. Zero

Q.

What is the lowest total resistance that can be secured by combinations of four coils of resistance $4\mathrm{\Omega },8\mathrm{\Omega },12\mathrm{\Omega },24\mathrm{\Omega }$?

Q.

The coefficient of self inductance of a solenoid is $0.18$ mH. If a rod of soft iron of relative permeability 900 is inserted in it, then the coefficient of self inductance will become nearly

1. 5.4 mH

2. 0.006 mH

3. 162 mH

4. 0.0002 mH

Q. Two coils connected in series have a resistance of 600ohm and 300ohm at 20degree celsius and temperature coefficient of 0.001 and 0.004 respectively.Find resistance of combination at 50degree celsius.what is the effective tempereture coefficient of the combination.

Q. When a current changes from + 2A to – 2A in 0.05s, an emf of 8V induced in a coil. The coefficient of self induction of coil is:

1. 0.1H
2. 0.2H
3. 0.4H
4. 0.8H

Q.

In an inductor of self inductance l = 2mH, current changes with time according to the relation $I=t^2{e}^{-t}$. The time at which the emf becomes zero is

1. 4s

2. 2s

3. 1s

4. 0.5s

Q.

When the numbers of coils get doubled then the self inductance

1. is doubled

2. is Halved

3. Becomes four times

4. Becomes quarter

Q. Electric field at a point varies as $r^{\circ }$ for

1. An electric dipole
2. A point charge
3. A line charge of infinite length
4. A plane infinite sheet of charge

Q.

How do you calculate the energy stored in a coil?

Q.

As shown in figure, a wire is bent to form a D-shaped closed loop, carrying current $I$, where the curved part is a semi-circle of radius $R$. The loop is placed in a uniform magnetic field $\overrightarrow{B}$, which is directed into the plane of the paper. The magnetic force felt by the closed loop is

1. $2IRB$
2. 0
3. $\frac{1}{2}IRB$
4. $IRB$

Q. 8.A bulb of 50W 10V is operated t 100V supply. If bulb glows with full intensity then used resistance in series is ?

Q.

if a bulb is connected in series with two bulbs parallels to each other which formula should I useto find which is more bright? why can't I use heat directly proportional to power and the relation of power in series and parallel? How do I know which relation to use in a question because heat is directly proportional to resistance in one formula and inversely proportional to it in other?

Q. Find r if 5pr=6pr-1

Q. Sir my question is like this

Why self induction is called inertia of electricity?

Q.

An inductor (L = 0.03H) and a resistor (r = 0.15 kW) are connected in series to a battery of 15V EMF in a circuit shown below. The key K₁ has been kept closed for a long time. Then at t = 0, K₁ is opened and key K₂ is closed simultaneously. At t = 1ms, the current in the circuit will be: (e⁵ ≅ 150)

1. 67 mA

2. 6.7 mA

3. 100 mA

4. 0.67 mA

Q. Two lamps, one rated 100 W at 220 V and the other 200 W at 220 V are connected in series and in parallel to an elctric main supply of 220 V. Find the current drawn in each case

Q. A thin walled copper wire pipe 3.0m long and 2cm in diameter carries a net charge of 5.8 MC distributed uniformly. what is electric field 8cm from pipe axis

Q. The magnetic field normal to the plane of a circular coil of $n$ turns and radius $r$ which carries a current $i$ is measured on the axis of coil at a very small distance $h$ from the centre of coil. The measured field is smaller than the magnetic field at centre by a fraction

1. $\frac{2r^2}{3h^2}$
2. $\frac{3r^2}{2h^2}$
3. $\frac{2h^2}{3r^2}$
4. $\frac{3h^2}{2r^2}$

Q.

What is the coefficient of mutual induction?

Q. Consider the following two statements:

$\left(A\right)$ An emf can be induced by moving a conductor in a magnetic field.

$\left(B\right)$ An emf can be induced by changing the magnetic field.

1. Both $A$ and $B$ are true.
2. $A$ is true, but $B$ is false.
3. $B$ is true, but $A$ is false.
4. Both $A$ and $B$ are false.