21.

A conductor lies along the z-axis at -1.5 ≤ z< 1.5 m and carries a fixed current of 10.An in^-az direction (see figure).
B = 3.0 x 10-4 e-0.2x a_y T, find the power required to move the conductor at constant speed to x = 2.0 , y = 0  in 5 x10^-3 s. Assume parallel motion along the x axis.

• 1.57 W

• 2.97 W

• 04.85 W

• 04.85 W

The coercivity of a small magnet where the ferromagnet gets demagnetized is 3 x 10³Am^-1.The current required to be passed in a solenoid of length 10 cm and number of turns 100, so that the magnet gets demagnetized when inside the solenoid, is

• 30 mA

• 60 mA

• 3 A

• 3 A

In the circuit shown here, the point C is kept connected to point A till the current flowing through the circuit becomes constant. Afterwards, suddenly point C is disconnected from point A and connected to point B at time t= 0. Ratio of the voltage across resistance and the inductor at t = L/R will be equal to 

• 

• 1

• -1

• -1

During the propagation of electromagnetic waves in a medium:

• Electric energy density is equal to the magnetic energy density.

• Both electric and magnetic energy densities are zero.

• Electric energy density is double of the magnetic energy density.

• Electric energy density is double of the magnetic energy density.

A thin convex lens made from crown glass  has focal length f. When it is measured in two different liquids having refractive indices 4/3 and 5/3, it has the focal lengths f₁ and f₂ respectively. The correct

•  f₁  = f₂ <f

•  f₁  >f and f₂ becomes negative

•  f₂  >f and f₁ becomes negative

•  f₂  >f and f₁ becomes negative

A green light is an incident from the water to the air – water interface at the critical angle (θ). Select the correct statement

• The entire spectrum of visible light will come out of the water at various angles to the normal.

• The spectrum of visible light whose frequency is less than that of green light will come out to the air medium

• The spectrum of visible light whose frequency is more than that of green light will come out to the air medium.

• The spectrum of visible light whose frequency is more than that of green light will come out to the air medium.

Two beams, A and B, of plane polarised light with mutually perpendicular planes of polarisation are seen through a Polaroid. From the position when the beam A has maximum intensity (and beam B has zero intensity), a rotation of Polaroid through 300 makes the two beams appear equally bright. If the initial intensities of the two beams are IA and IB respectively, then I_A/I_B equals:

• 3

• 3/2

• 1

• 1

The radiation corresponding to 3 → 2 transition of hydrogen atom falls on a metal surface to produce photoelectrons. These electrons are made to enter a magnetic field of 3 x 10^-4 T. If the radius of the largest the circular path followed by these electrons is 10.0 mm, the work function of the metal is close to:

• 1.8 eV

• 1.1 eV

• 0.8 eV

• 0.8 eV

Hydrogen (₁H¹), deuterium (₁H²), singly ionised helium (₂He⁴⁺) and doubly ionised lithium (₃Li⁸)²⁺ all have one electron around the nucleus. Consider an electron transition from n =2 to n=1. If the wavelengths of emitted radiation are λ₁,λ₂,λ₃ andλ₄, respectively for four elements, then approximately which one of the following is correct?

•  4λ₁=2λ₂=2λ₃ =λ₄

•  λ₁=2λ₂=2λ₃ =λ₄

•  λ₁=λ₂=4λ₃ =9λ₄

•  λ₁=λ₂=4λ₃ =9λ₄

The forward biased diode connection is