15.  Plastics and glasses are
A. crystalline
B. liquid
C. solid solution
D. amorphous

---

16. The Miller indices of the diagonal plane of a cube are
A.1110
B.110
C.101
D.11

---

17.  As the temperature increases, the vibrational frequency of the atoms in a solid
A. decreases
B. increases
C. may increase or decrease
D. remains constant

---

18.  At low temperatures, the mean free path and collision time are proportional to where T is the temperature in deg K
A. ferrimagnetic
B. diamagnetic
C. paramagnetic
D. ferromagnetic

---

19.  Which of the following statements is correct?
A. Copper has partially filled conduction band.
B. Diamond has completely filled conduction band but empty valence band
C. Silicon has a partially filled conduction band and an empty valence band.
D. The energy gap betwen conduction and valence bands in diamond is smaller than in silicon.

---

20.  X-rays are produced by I. bombarding metallic targets with high speed electrons 2. decelerating fast moving electrons 3. accelerating electrons to hig speeds 4. heating a filament to high temperature Select the correct answer using the codes given below :Codes :
A. 1 and 2 only
B. 3 and 4 only
C. 2 and 3 only
D. 1 and 4 only

---

21. Which of the following is not electromagnetic in nature?I. alpha raya 2. X-rays 3. gamma rays 4. cathode rays Select the correct answer using the codes given below : Codes :
A. 1 and 2 rays
B. 2 and 3 only
C. 3 and 3 only
D. 1 and 4 only

---