Carbon, silicon and germanium atoms have four valence electrons each. Their valence and conduction bands are separated by energy band gaps represented by _{${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}} , {\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Si}} \mathrm{and} {\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Ge}}$} respectively. Which one of the following relationships is true in their case?

• ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}} > {\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{si}}$

• ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}} = {\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Si}}$

• ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}} < {\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Ge}}$

• ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}} > {\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Si}}$

Choose the only false statement from the following

• Substances with energy gap ofthe order of 10 eV are insulators 

• The conductivity of a semiconductor increases with  increases in temperature

• In conductors the valence and conduction bands may overlap

• The resistivity of a semiconductor increases with increase in temperature

The total energy of an electron in the first excited state of hydrogen is about -3.4 eV. Its kinetic energy in this state is

• -3.4 eV

• -6.8 eV

• 6.8 eV

• 3.4 eV

Which logic gate is represented by the following combination of logic gates?

• OR

• NOR

• AND

• NAND

The principle of LASER action involves

• amplification of particular frequency emitted by the system

• population inversion

• stimulated emission

• All of the above

Which of the following is unipolar transistor?

• p-n-p transistor

• n-p-n transistor

• Field effect transistor

• Point contact transistor

The truth table given below is for (A and B are the inputs, Y is the output)

• NOR

• AND

• XOR

• NAND

Which logic gate is represented by the following combination of logic gates?

• OR

• NOR

• AND

• NAND

The reason of current flow in p-n junction in forward bias is

• drifting of charge carriers

• drifting of minority charge carriers

• diffussion of charge carriers

• All of the above

A change of 8.0 mA in the emitter current brings a change of 7. 9 mA in the collector current. The value of a will be

• 0.96

• 0.93

• 0.90

• 0.99