61. A piece of copper and another of germanium are cooled from room temperature to $$77K,$$ the resistance of
A
copper increases and germanium decreases
B
each of them decreases
C
each of them increases
D
copper decreases and germanium increases
Answer :
copper decreases and germanium increases
62.
The following truth table corresponds to the local gate
| Inputs | Output | |
|---|---|---|
| A | B | Y |
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 1 |
A
NAND
B
OR
C
AND
D
XOR
Answer :
OR
63. In forward biasing of the $$p-n$$ junction
A
the positive terminal of the battery is connected to $$n$$-side and the depletion region becomes thin
B
the positive terminal of the battery is connected to $$n$$-side and the depletion region becomes thick
C
the positive terminal of the battery is connected to $$p$$-side and the deplection region become thin
D
the positive terminal of the battery is connected to $$p$$-side and the depletion region becomes thick
Answer :
the positive terminal of the battery is connected to $$p$$-side and the deplection region become thin
64. A radar has a power of $$1kW$$ and is operating at a frequency of $$10\,GHz.$$ It is located on a mountain top of height $$500\,m.$$ The maximum distance upto which it can detect object located on the surface of the earth (Radius of earth = $$6.4 \times {10^6}m$$ ) is:
A
$$80\,km$$
B
$$16\,km$$
C
$$40\,km$$
D
$$64\,km$$
Answer :
$$80\,km$$
65. A transistor has $$\beta = 40.$$ A change in base current of $$100\,\mu A,$$ produces change in collector current
A
$$40 \times 100\,{\text{microampere}}$$
B
$$\left( {100 - 40} \right)\,{\text{microampere}}$$
C
$$\left( {100 + 40} \right)\,{\text{microampere}}$$
D
$$\frac{{100}}{{40}}\,{\text{microampere}}$$
Answer :
$$40 \times 100\,{\text{microampere}}$$
66. For a cubic crystal structure which one of the following relations indicating the cell characteristic is correct ?
A
$$a \ne b \ne c\,{\text{and}}\,\alpha \ne \beta \,{\text{and}}\,\gamma \ne {90^ \circ }$$
B
$$a \ne b \ne c\,{\text{and}}\,\alpha \ne \beta {\text{ = }}\gamma = {90^ \circ }$$
C
$$a = b = c\,{\text{and}}\,\alpha \ne \beta \ne \gamma = {90^ \circ }$$
D
$$a = b = c\,{\text{and}}\,\alpha = \beta {\text{ = }}\gamma = {90^ \circ }$$
Answer :
$$a = b = c\,{\text{and}}\,\alpha = \beta {\text{ = }}\gamma = {90^ \circ }$$
67. If a full wave rectifier circuit is operating from $$50\,Hz$$ mains, the fundamental frequency in the ripple will be
A
$$70.7\,Hz$$
B
$$100\,Hz$$
C
$$25\,Hz$$
D
$$59\,Hz$$
Answer :
$$100\,Hz$$
68. By increasing the temperature, the specific resistance of a conductor and a semiconductor
A
increases for both
B
decreases for both
C
increases, decreases
D
decreases, increases
Answer :
increases, decreases
69.
A full-wave rectifier circuit along with the out-put is shown in Figure. The contribution $$\left( s \right)$$ from the diode 1 is (are)
A
$$C$$
B
$$A,C$$
C
$$B,D$$
D
$$A,B,C,D$$
Answer :
$$A,C$$
70. A transistor is operated in common emitter configuration at $${V_C} = 2\,V$$ such that a change in the base current from $$100\,\mu A$$ to $$300\,\mu A$$ produces a change in the collector current from $$10\,mA$$ to $$20\,mA.$$ The current gain is
A
50
B
75
C
100
D
25
Answer :
50