Electro magnetic induction practice · Medium

A metal disc of radius $R$ rotates with an angular velocity $\omega$ about an axis perpendicular to its plane passing through its centre in a magnetic field $B$ acting perpendicular to the plane of the disc. Calculate the induced emf between the rim and the axis of the disc.

Statement I: A hanging spring is attached to a battery and switch. On closing the switch a current suddenly flows in the spring, as a result spring compresses.

Statement II: When two current carrying coils are placed close to each other in same plane, then they attract each other if sense of current is same in both.

Assertion(A): The possibility of an electric bulb fusing is higher at the time of switching on and off.

Reason(R): Inductive effects produce a large current at the time of switch-on and switch-off.

A coil of 1200 turns and mean area of $500\,\,\mathrm{c}{\mathrm{m}^2}$ is held perpendicular to a uniform magnetic field of induction $4 \times {10^{ - 4}}\,\,\mathrm{T}.$ The resistance of the coil is 20 ohm. When the coil is rotated through ${180^0}$ in the magnetic field is 0.1 seconds the average electric current (in MA) induced is

If $0.1 \mathrm{~J}$ of energy is stored for the flow of current of $0.2 \mathrm{~A}$ in an inductor, then its inductance value is

What is the self inductance of a solenoid of length $\mathrm{31}\mathrm{.4 }\,\mathrm{cm}$, area of cross-section ${10^{ - 3}}\,{\mathrm{m}^2}$ and total number of turns ${10^3}$ ?

A solenoid of radius $\mathrm{R}$ has $\mathrm{n}$ turns per unit length, then the self-inductance of the solenoid per unit length is

Assertion (A): Whenever the magnetic flux linked with a closed coil changes there will be an induced emf as well as an induced current.

Reason (R): According to Faraday, the induced emf is inversely proportional to the rate of change of magnetic flux linked with a coil.

Assertion: Unlike charges are projected in opposite direction in transverse magnetic field, then they are deflected in same direction.

Reason: If a voltmeter connected across two peripheral points of faraday copper disc generator, its reading is zero.

Assertion: A thin aluminum disc, spinning freely about a central pivot, is quickly brought to rest when placed between the poles of a strong $U$-shaped magnet.

Reason: A current induced in a disc rotating in a magnetic field produces a torque which tends to oppose the disc's motion.

Which of the following is true for induced electric fields due to time varying magnetic field?

An a.c. generator is made up of a 1000 -turn coil with a $3 m^2$ cross-sectional area that rotates at $60 \mathrm{~rad} \mathrm{s}^{-1}$ in a uniform magnetic field of $0.04 \mathrm{~T}$. The coil has a resistance of 500. Calculate the generator's maximum current draw.

S-I: When a coil of $n$ turns is placed in a changing magnetic field, an e.m.f. is developed in each turn so that the total e.m.f. developed between the terminals of the coil is equal to the sum of the e.m.f. developed in individual turns.

S-II: The induced charge is always independent of the time for which the flux has changed through the coil.

The phase difference between the flux linked with a coil rotating in a uniform magnetic field and induced $emf$ produce in it is

Assertion : If a charged particle is released from rest in a time varying magnetic field, it moves in a circle.

Reason : In a time varying magnetic field, conservative electric field is induced.

The number of turns of primary and secondary coils of a transformer are $\mathrm{5}\,\,\mathrm{and}\,\mathrm{10}$ respectively and the mutual inductance of the transformer is $25\,\,henry$. Now the number of turns in the primary and secondary of the transformer are made $\mathrm{10}\,\,\mathrm{and}\,\mathrm{5}$ respectively. The mutual inductance of the transformer in $henry$ will be

If $\phi=t^2$ and $R=2 \Omega$ then find induced heat in $1 \mathrm{sec}$.

Which one of the following is not true?

Assertion: Induced electric field is non conservative.

Reason: $\oint \overrightarrow{\mathrm{E}} \cdot \mathrm{d} \vec{l} \neq 0$

The series combination of resistance $R$ and inductance $L$ is connected to an alternating source of emf $e = 311\,\sin (100\pi t).\,$ If the value of wattles current is 0.5 A and the impedance of the circuit is $311\,\Omega$, the power factor will be:-

A $50\,\,Hz$ ac current of peak value $\mathrm{2 A}$ flows through one of the pair of coils. If the mutual inductance between the pair of coils is $150\,\,mH$, then the peak value of voltage induced in the second coil is

A current carrying ring is placed in a horizontal plane. A charged particle is dropped along the axis of the ring to fall under the influence of gravity

A bar magnet is released into a copper ring directly below it. The acceleration of the magnet will be

Lenz’s law of electromagnetic induction corresponds to the

A coil of 1200 turns and mean area of $500\,\,\mathrm{c}{\mathrm{m}^2}$ is held perpendicular to a uniform magnetic field of induction $4 \times {10^{ - 4}}\,\,\mathrm{T}.$ The resistance of the coil is 20 ohm. When the coil is rotated through ${180^0}$ in the magnetic field is 0.1 seconds the average electric current (in MA) induced is

Armature current in dc motor will be maximum when

The back e.m.f. induced in a coil, when current changes from $1 \mathrm{~A}$ to $0 \mathrm{~A}$ in 1 milli-second is $4 \mathrm{~V}$. The self-inductance of the coil is ____

A metallic metre stick moves with a velocity of $2 \mathrm{~m} \mathrm{~s}^{-1}$ in a direction perpendicular to its length and perpendicular to a uniform magnetic field of magnitude $0.2 \mathrm{~T}$. Find the emf induced between the ends of the stick.

When the number of turns in the two circular coils closely wound are doubled (in both), their mutual inductance becomes

Magnetic flux linked with a coil is $\phi = 5\,{t^2} + 2\,t + 3$, where $t$ is second and $\phi$ is in weber. At time $t = 1\mathrm{ }s$, the value of induced emf in volt