A solid that is not transparent to visible light and whose electrical conductivity increases with temperature is formed by

ionic binding
covalent binding
metallic binding
vander Waal’s binding

The current gain β may be defined as

the ratio of change in collector current to the change in emitter current for a constant collector voltage in a common base arrangement.
the ratio of change in collector current to the change in the base current at constant collector voltage in a common emitter circuit
the ratio of change in emitter current to the change in base current for constant emitter voltage in common emitter circuit.
the ratio of change in base current to the change in collector current at constant collector voltage in common emitter circuit.

Two junction diodes one of Germanium (Ge) and other of silicon (Si) are connected as shown in figure to a battery of emf 12 V and a load resistance 10 k Ω. The germanium diode conducts at 0.3 V and silicon diode at 0.7 V. When a current flows in the circuit, the potential of terminal Y will be

12 V
11 V
11.3 V
11.7 V

The following configuration of gate is equivalent to

NAND gate
XOR gate
OR gate
NOR gate

Solution

Assuming that the silicon diode having resistance of 20 Ω, the current through the diode is(knee voltage 0.7 V)

0 mA
10 mA
6.5 mA
13.5 mA

Solution

Metallic solids are always opaque because

they reflect all the incident light.
they scatter all the incident light.
the incident light is readily absorbed by the free electrons in a metal.
the energy band traps the incident.

If A is the atomic mass number of anelement, N is the Avogadro number and a is the lattice parameter, then the density of the element, if it has bcc crystal structure, is