The impedance of a series L-C-R circuit is

In a circuit, the phase difference between the alternating current and the source voltage is π/ 2 Which of the following cannot be the element(s) of the circuit?

Which of the following has maximum penetrating power?

A coil of resistance 400Ω is placed in a magnetic field. If the magnetic flux Φ linked with the coil varies with times t (see) as Φ = 50t² + 4, the current in the coil at t = 2 sec is

A diamagnetic material in a magnetic field moves

Lines of force, due to earth's horizontal magnetic field, are

What is not possible in a transformer?

Two coils are placed close to each other. The mutual inductance of the pair of coils depends upon

The frequency of a.c. generated depends on

Out of the following options which one can be used in produce a propagating electromagnetic wave?

A stationary charge produces only an electrostatic field while a charge in uniform motion produces a magnetic field, that does not change with time. An oscillating charge is an example of accelerating charge. It produces an oscillating magnetic field, which in turruproduces an oscillating electric fields and so on. The oscillating electric and magnetic fields regenerate each other as a wave which propagates through space.

(i) Magnetic field in a plane electromagnetic wave is given by \(\vec{B}=B_{0} \sin (k x+\omega t) \hat{j} \mathrm{~T}\) Expression for corresponding electric field will be (Where C is speed of light.)

\((a) \vec{E}=-B_{0} c \sin (k x+\omega t) \hat{k} \mathrm{~V} / \mathrm{m}\)	\((b) \vec{E}=B_{0} c \sin (k x-\omega t) \hat{k} \mathrm{~V} / \mathrm{m}\)
\((c) \vec{E}=\frac{B_{0}}{c} \sin (k x+\omega t) \hat{k} \mathrm{~V} / \mathrm{m}\)	\((d) \vec{E}=B_{0} c \sin (k x+\omega t) \hat{k} \mathrm{~V} / \mathrm{m}\)

(ii) The electric field component of a monochromatic radiation is given by \(\vec{E}=2 E_{0} \hat{i} \cos k z \cos \omega t\) .Its magnetic field \(\vec{B}\) is then given by

\((a) \frac{2 E_{0}}{c} \hat{j} \cos k z \cos \omega t\)	\((b) \frac{2 E_{0}}{c} \hat{j} \sin k z \cos \omega t\)
\((c) \frac{2 E_{0}}{c} \hat{j} \sin k z \sin \omega t\)	\((d) -\frac{2 E_{0}}{c} \hat{j} \sin k z \sin \omega t\)

(iii) A plane em wave of frequency 25 MHz travels in a free space along x-direction. At a particular point in space and time, \(E=(6.3 \hat{j}) \mathrm{V} / \mathrm{m}\) What is magnetic field at that time?

\((a) 0.095 \mu \mathrm{T}\)

\((b) 0.124 \mu \mathrm{T}\)

\((c) 0.089 \mu \mathrm{T}\)

\((d) 0.021 \mu \mathrm{T}\)

(iv) A plane electromagnetic wave travelling along the x-direction has a wavelength of 3 mm. The variation in the electric field occurs in the y-direction with an amplitude 66 V m^-1. The equations for the electric and magnetic fields as a function of x and t are respectively

\((a) E_{y}=33 \cos \pi \times 10^{11}\left(t-\frac{x}{c}\right), B_{z}=1.1 \times 10^{-7} \cos \pi \times 10^{11}\left(t-\frac{x}{c}\right)\)

\((b) E_{y}=11 \cos 2 \pi \times 10^{11}\left(t-\frac{x}{c}\right), \quad B_{y}=11 \times 10^{-7} \cos 2 \pi \times 10^{11}\left(t-\frac{x}{c}\right)\)

\((c) E_{x}=33 \cos \pi \times 10^{11}\left(t-\frac{x}{c}\right), \quad B_{x}=11 \times 10^{-7} \cos \pi \times 10^{11}\left(t-\frac{x}{c}\right)\)

\((d) E_{y}=66 \cos 2 \pi \times 10^{11}\left(t-\frac{x}{c}\right), \quad B_{z}=2.2 \times 10^{-7} \cos 2 \pi \times 10^{11}\left(t-\frac{x}{c}\right)\)

(v) A plane electromagnetic wave travels in free space along x-axis. At a particular point in space, the electric field along y-axis is 9.3 V m^-1. The magnetic induction (B) along z-axis is

(a) 3.1 x 10-8 T

(b) 3 x 10-5 T

(c) 3 x 10-6 T

(d) 9.3 x 10-6 T

A transformer is an electrical device which is used for changing the a.c. voltages. It is based on the phenomenon of mutual induction i.e. whenever the amount of magnetic flux linked with a coil changes, an e.m.f is induced in the neighbouring coil. For. an ideal transformer, the resistances of the primary and secondary windings are negligible.

It can be shown that \(\frac{E_{s}}{E_{p}}=\frac{I_{p}}{I_{s}}=\frac{n_{s}}{n_{p}}=k\)
where the symbols have their standard meanings.
For a step up transformer \(n_{s}>n_{p} ; E_{s}>E_{p} ; k>1 ; \quad \therefore I_{s}
For a step down transformer \(n_{s}
The above relations are on the assumptions that efficiency of transformer is 100%.
lentlac ,effciency \(\eta=\frac{\text { output power }}{\text { intput power }}=\frac{E_{s} I_{s}}{E_{p} I_{p}}\)
(i) Which of the following quantity remains constant in an ideal transformer?

(a) Current

(b) Voltage

(c) Power

(d) All of these

(ii) Transformer is used to

(a) convert ac to dc voltage	(b) convert de to ac voltage
(c) obtain desired dc power	(d) obtain desired ac voltage and current

(iii) The number of turns in primary coil of a transformer is 20 and the number of turns in a secondary is 10. If the voltage across the primary is 220 ac V, what is the voltage across the secondary?

(a) 100 ac V

(b) 120 ac V

(c) 110 ac V

(d) 220 ac V

(iv) In a transformer the number of primary turns is four times that of the secondary turns. Its primary is connected to an a.c. source of voltage V. Then

(a) current through its secondary is about four times that of the current through its primary

(b) voltage across its secondary is about four times that of the voltage across its primary.

(c) voltage across its secondary is about two times that of the voltage across its primary

(d) voltage across its secondary is about \(\frac{1}{2 \sqrt{2}}\) times that of the voltage across its primary

(v) A transformer is used to light 100 W-110 V lamp from 220 V mains. If the main current is 0.5 A, the efficiency of the transformer is

(a) 95%

(b) 99%

(c) 90%

(d) 96%

When a current I flows through a coil, flux linked with it is \(\phi=L I,\) where L is a constant known as self-inductance of the coil. Any change in current sets up an induced emf in the coil. Thus, self-inductance of a coil is the induced emf set up in it when the current passing through it changes at the unit rate. It is a measure of the opposition to the growth or the decay of current flowing through the coil. Also, value of self-inductance depends on the number of turns in the solenoid, its area of cross-section, and the relative permeability of its core material.

(I) The inductance in a coil plays the same role as 

(a) inertia in mechanics	(b) energy in mechanics
(c) momentum in mechanics	(d) force in mechanics

(ii) A current of 2.5 A flows through a coil of inductance 5 H. The magnetic flux linked with the coil is

(a) 0.5 Wb

(b) 12.5 Wb

(c) zero

(d) 2 Wb

(iii) The inductance L of a solenoid depends upon its radius R as

\(\text { (a) } L \propto R\)

\(\text { (b) } L \propto 1 / R\)

\(\text { (c) } L \propto R^{2}\)

\(\text { (d) } L \propto R^{3}\)

(iv) The unit of self-inductance is

(a) weber ampere

(b) weber-1 ampere

(c) ohm second

(d) farad

(v) The induced e.m.f in a coil of 10 henry inductance in which current varies from 9 A to 4 A in 0.2 second is

(a) 200 V

(b) 250 V

(c) 300 V

(d) 350 V

The field of a hollow wire with constant current is homageneous
Curves in the graph shown give, as functions of radius distance r, the magnitude B of the magnetic field inside and outside four long wires a, b, c and d, carrying currents that are uniformly distributed across the cross sections of the wires. Overlapping portions of the plots are indicated by double labels.

(i) Which wire has the greatest magnitude of the magnetic field on the surface?

(a) a

(b) b

(c) c

(d) d

(ii) The current density in a wire a is

(a) greater than in wire c

(b) less than in wire

(c) equal to that in wire c

(d) not comparable to that of in wire c due to lack of information

(iii) Which wire has the greatest radius?

(a) a

(b) b

(c) c

(d) d

(iv) A direct current I flows along the length of an infinitely long straight thin walled pipe, then the magnetic field is

(a) uniform throughout the pipe but not zero

(b) zero only along the axis of the pipe

(c) zero at any point inside the pipe

(d) maximum at the centre and minimum at the edges

(v) In a coaxial, straight cable, the central conductor and the outer conductor carry equal currents in opposite direction. The magnetic field is zero

(a) outside the cable	(b) inside the inner conductor
(c) inside the outer conductor	(d) in between the two conductor.

Assertion : The electromagnetic wave is transverse in nature.
Reason : Electromagnetic wave propagates parallel to the direction of electric and magnetic fields.
Codes:
(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
(c) If the Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect.

Assertion : We use a thick wire in the secondary of a step down transformer to reduce the produced heat.
Reason : When the plane of the armature coil is parallel to the line of force of magnetic field, the magnitude of induced e.m.f. is maximum.
Codes:
(a) If both Assertion & Reason are true & the Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are true but Reason is not a correct explanation of the Assertion.
(c) If Assertion is true but the Reason is false.
(d) If Assertion & Reason both are false.

Assertion : Whenever magnetic flux linked with the coil changes with respect to time, then an emf is induced in it.
Reason : According to lenz law, the direction of induced current in any coil in such a way that it always oposses the cause by which it is produced.
Codes:
(a) If both Assertion & Reason are true & the Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are true but Reason is not a correct explanation of the Assertion.
(c) If Assertion is true but the Reason is false.
(d) If Assertion & Reason both are false.

Assertion : An induced emf appears in any coil in which the current is changing.
Reason : Self induction phenomenon obeys Faraday’s law of induction.
Codes:
(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
(c) If the Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect.

Assertion : The power in an ac circuit is minimum if the circuit has only a resistor.
Reason: Power of a circuit is independent of the phase angle.
Codes:
(a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct.

Assertion (A) : Infrared waves sometimes referred as heat waves.
Reason (R) : Infrared waves heat up the earth surface
Codes:
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is NOT the correct explanation of A
(c) A is true but R is false
(d) A is false and R is also false

Assertion (A) : A bulb connected in series with a solenoid is connected to A.c. source. If a soft iron core is introduced in the solenoid, the bulb will glow brighter.
Reason (R) : On introducing soft iron core in the solenoid, the inductance decreases.
Codes:
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is NOT the correct explanation of A
(c) A is true but R is false
(d) A is false and R is also false

Assertion (A) : Step-down transformer increases the current.
Reason (R) : Transformer obeys the law of conservation of energy.
Codes:
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is NOT the correct explanation of A
(c) A is true but R is false
(d) A is false and R is also false

Assertion (A) : The true geographic north direction is found by using a compass needle.
Reason (R) : The magnetic meridian of the earth is along the axis of rotation of the earth.
Codes:
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is NOT the correct explanation of A
(c) A is true but R is false
(d) A is false and R is also false

Assertion (A) : Earth's magnetic field does not affect the working of a moving coil galvanometer.
Reason (R) : The earth's magnetic field is <Iuiteweak as compared to magnetic field produced in the moving coil galvanometer.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but Ris NOT the correct explanation of A
(c) A is true but R is false
(d) A is false and R is also false