If the work functions of three photosensitive materials are 1 eV, 2 eV and 3 eV respectively, then the ratio of the respective frequencies of light that produce photoelectrons of maximum kinetic energy of 1 eV from each of them is

• 1 : 2 : 3

• 2 : 3 : 4

• 1 : 1 : 1

• 3 : 2 : 1

During β⁻ emission,

• a neutron in the nucleus decays emitting an electron

• an atomic electron is ejected

• an electron already present within the nucleus is ejected

• a part of the binding energy of the nucleus is converted into an electron

The binding energy per nucleon of ¹⁶O is 7.97 MeV and that of ¹⁷O is 7.75 MeV. The energy in MeV required to remove a neutron from ¹⁷O is

• 3.52 

• 3.64

• 4.23

• 7.86

If the ratio of the radius of a nucleus with 61 neutrons to that of helium nucleus is 3, then the atomic number of this nucleus is

• 27

• 47

• 51

• 61

The electron density of intrinsic semiconductor at room temperature is 10¹⁶ m^-3. When doped with a trivalent impurity, the electron density is decreased to 10¹⁴ m^- at the same temperature. The majority carrier density is

• 10¹⁶ m^-3

• 10¹⁸ m^-3

• 10²¹ m^-3

• 10²⁰ m^-3

In a Zener diode regulated power supply, unregulated DC input of 10 V is applied. If the resistance (R_s) connected in series with a Zener diode is 200 Ω and the Zener voltage V_z =5V, the current across the resistance R_s is

• 15 mA

• 10 mA

• 25 mA

• 5 mA

The circuit gives the output as that

• AND gate

• OR gate

• NAND gate

• NOR gate

To detect light of wavelength 500 nm, the photodiode must be fabricated from a semiconductor of minimum bandwidth of

• 1.24 eV

• 0.62 eV

• 2.48 eV

• 3.2 eV

69.

If the height of TV tower is increased by 21%, then the transmission range is enhanced by

• 10 %

• 5 %

• 15 %

• 25 %

The range of a communication system can be extended by a

• modulator

• transmitter

• repeater

• receiver