21.

The electric field at a distance 3R/2 from the centre of a charged conducting spherical shell of radius R is E. The electric field at a distance R/2 from the centre of the sphere is

• zero

• E

• E/2

• E/2

The electric field of an electromagnetic wave in free space is given by , where t and x are in seconds and meters respectively. It can be inferred that

1) the wavelength λ is 188.4 m.
2)The wave number k is 0.33 rad/m.
3)The wave amplitude is 10 V /m.
4)The wave is propagating along +x direction

• (3) and (4)

• (1) and (2) 

• (2) and (3)

• (2) and (3)

A ray of light is incident on a 60^o prism at the minimum deviation position. The angle of refraction at the first face (ie, incident face) of the prism is

• zero

• 30^o

• 45^o

• 45^o

For transistor action

A) Base, emitter and collector regions should have similar size and doping concentrations.

B) The base region must be very thin and lightly doped.

C) The emitter-base junction is forward biased and base -collector junction is reverse biased

D) Both the emitter-base junction as well as the base-collector junction are forward biased.

• (D) and (A)

• (A) and (B)

• (B) and (C)

• (B) and (C)

The decay constant of a ratio isotope is λ. If A₁ and A₂ are its activities at times t₁ and t₂ respectively, te number of nuclei which have decayed during the time (t₁-t₂)

• A₁t₁ - A₂t₂

• A₁ - A₂

• (A₁ - A₂)/λ

• (A₁ - A₂)/λ

The binding energy per nucleon in deuterium and helium nuclei are 1.1 MeV and 7.0 MeV, respectively. When two deuterium nuclei fuse to form a helium nucleus the energy released in the fusion is

• 23.6 MeV

• 2.2 MeV

• 28.0 MeV

• 28.0 MeV

The electron in the hydrogen atom jumps from excited state (n=3) to its ground state (n=1) and the photons thus emitted irradiate a photosensitive material. If the work functions of the material is 5.1 eV, the stopping potential is estimated to be (the energy of the electron is nth state E_n = -13.6/n² eV)

• 5.1 V

• 12.1 V

• 17.2 V

• 17.2 V

When monochromatic radiation of intensity I falls on a metal surface, the number of photoelectrons and their maximum kinetic energy and N and T respectively. If the intensity of radiation is 2I, the number of emitted electrons and their maximum kinetic energy are respectively

• N and 2T

• 2N and T

• 2N and 2T

• 2N and 2T

The speed of light in media M₁ and M₂ is 1.5 x 10⁸ m /s respectively. A ray of light enters from medium M₁ and M₂ at incidence angle i. If the ray suffers total internal reflection the value of i is 

• equal to sin^-1 (2/3)

• equal to or less than sin^-1 (3/5)

• equal to or greater than sin^-1 (3/4)

• equal to or greater than sin^-1 (3/4)

The following figure shows a logic gate circuit with two inputs A and B the output Y. The voltage waveforms of A, B and Y are as given


The logic gate is

•  NOR gate

• OR Gate

• AND gate

• AND gate