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1

### AIPMT 2006

The following figure shows a logic gate circuit with two inputs A and B and the output C. The voltage waveforms of A, B and C are as shown below. The logic circuit gate is
A
OR gate
B
AND gate
C
NAND gate
D
NOR gate

## Explanation

The truth table corresponding to waveform is given by

$$\matrix{ A & B & C \cr 1 & 1 & 1 \cr 0 & 1 & 0 \cr 1 & 0 & 0 \cr 0 & 0 & 0 \cr }$$

$$\therefore$$ The given logic circuit gate is AND gate.
2

### AIPMT 2005

In a p-n junction photo cell, the value of the photo-electromotive force profuced by monochromatic light is proportional to
A
The barrier voltage at the p-n junction.
B
The intensity of the light falling on the cell.
C
The frequency of the light falling on the cell.
D
The voltage applied at the p-n junction.

## Explanation

Electromotive force depends on intensity of light that falls on it and does not depend on the frequency.
3

### AIPMT 2005

Copper has face centered cubic (fcc) lattice with interatomic spacing equal to 2.54 $$\mathop A\limits^ \circ$$. The value of lattice constant for this lattice is
A
2.54 $$\mathop A\limits^ \circ$$
B
3.59 $$\mathop A\limits^ \circ$$
C
1.27 $$\mathop A\limits^ \circ$$
D
5.08 $$\mathop A\limits^ \circ$$

## Explanation

Lattice constant for (f.c.c.)

= a = interatomic spacing $$\times$$ $$\sqrt 2$$ = 3.59 $$\mathop A\limits^ \circ$$
4

### AIPMT 2005

Carbon, silicon and germanium atoms have four valence electrons each. Their valence and conduction bands are separated by energy band gaps represented by (Eg)C, (Eg)si and (Eg)Ge respectively. Which one of the following relationships is true in their case?
A
(Eg)C > (Eg)Si
B
(Eg)C < (Eg)Si
C
(Eg)C = (Eg)Si
D
(Eg)C < (Eg)Ge.

## Explanation

Band gap of carbon is 5.5 eV while that of silicon is 1.1 eV

$$\therefore$$ (Eg)C $$>$$ (Eg)Si

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