Sodium has body centred packing.Distance between two nearest atom is $3.7\stackrel{0}{A}$. The lattice parameter is 

1. 6.8 $\stackrel{0}{A}$                                     

2. 4.3 $\stackrel{0}{A}$

3. 3.0 $\stackrel{0}{A}$                                     

4. 8.6 $\stackrel{0}{A}$

If the lattice parameter for a crystalline structure is $3.6 \stackrel{0}{A},$ then the atomic radius in fcc crystal is

1. $1.81\stackrel{0}{A}$

2. $2.10\stackrel{0}{A}$

3. $2.92\stackrel{0}{A}$

4. $1.27\stackrel{0}{A}$

A p-n photodiode is made of a material with a band gap of 2.0 eV. The minimum frequency of the radiation that can be absorbed by the material is nearly

1. $10\times {10}^{14} Hz$                              2. $5\times {10}^{14} Hz$

3. $1\times {10}^{14} Hz$                                4. $20\times {10}^{14} Hz$

The electrical resistance of depletion layer is large because:

1. It has no charge carriers

2. It has a large number of charge carriers

3. It contains electrons as charge carriers

4. It has holes as charge carriers

Avalanche breakdown is due to 

(1) Collision of minority charge carrier

(2) Increase in depletion layer thickness

(3) Decrease in depletion layer thickness

(4) None of these