61.

The wavelength of red light from He-Ne laser is 633 nm in air but 474 nm in the aqueous humor inside the eye ball. Then the speed of red light through the aqueous humor is

• 3 × 10⁸ m/s

• 1.34 × 10⁸ m/s

• 2.25 × 10⁸ m/s

• 2.5 × 10⁸ m/s

The radius of curvature of the convex face of a planoconvex lens is 15 cm and the refractive index of the material is 1.4.Then the power of the lens in dioptre is

• 1.6

• 1.66

• 2.6

• 2.66

The threshold wavelength for photoelectric emission from a material is 4800 . Photoelectrons will be emitted from the material, when it is illuminated with light from a

• 40 W blue lamp

• 40 W green lamp

• 100 W red lamp

• 100 W yellow lamp

The energy released in the fission of 1 kg of ₉₂U²³⁵ is (energy per fission = 200 MeV)

• 5.1 × 10²⁶ eV

• 5.1 × 10²⁶ J

• 8.2 × 10¹³ J

• 8.2 × 10¹³ MeV

The nuclear radius of a certain nucleus is 7.2 fm and it has charge of 1.28 x 10^-17 C. The number of neutrons inside the nucleus is

• 136

• 142

• 140

• 132

Which one of the following statement is true, if half-life of a radioactive substance is 1 month ?

• 7/8^th part of the substance will disintegrate in 3 months

• 1/8^th part of the substance will remain undecayed at the end of 4 months

• The substance will disintegrate completely in 4 months

• 1/16^th part of the substance will remain undecayed at the end of 3 months

A common emitter amplifier gives an output of 3 V for an input of 0.01 V. If β of the transistor is 100 and the input resistance is 1 kΩ, then the collector resistance is

• 1 kΩ

• 3 kΩ

• 30 kΩ

• 30 kΩ

The combination of the following gates produces

• AND gate

• NAND gate

• NOR gate

• OR gate

In satellite communication

1. the frequency used lies between 5 MHz and 10 MHz.
2. the uplink and downlink frequencies are different.
3. the orbit of geostationary satellite lies in the equatorial plane at an inclination of 0°.

In the above statements

• only 2 and 3 are true

• all are true

• only 2 is true

• only 1 and 2 are true

The principle used in the transmission of signals through an optical fibre is

• total internal reflection

• reflection

• refraction

• dispersion