1
MCQ (Single Correct Answer)

AIPMT 2009

A p-n photodiode is fabricated from a semiconductor with a band gap of 2.5 eV. It can detect a signal of wavelength
A
4000 nm
B
6000 nm
C
4000 $$\mathop A\limits^ \circ $$
D
6000 $$\mathop A\limits^ \circ $$

Explanation

$$\lambda $$max = $${{hc} \over E}$$

= $${{6.6 \times {{10}^{ - 34}} \times 3 \times {{10}^8}} \over {2.5 \times 1.6 \times {{10}^{ - 19}}}}$$

= 5000 $$\mathop A\limits^o $$

Now the wavelength detected by photodiode be less than $$\lambda $$max, hence it can detect a signal of wave length 4000 $$\mathop A\limits^o $$.
2
MCQ (Single Correct Answer)

AIPMT 2009

A transistor is operated in common-emitter configuration at VC = 2V such that a change in the base current from 100 $$\mu $$A to 200 $$\mu $$A produces a change in the collector current from 5 mA to 10 mA. The current gain is
A
100
B
150
C
50
D
75

Explanation

Current gain, $$\beta $$ = $${{\Delta {I_C}} \over {\Delta {I_B}}}$$

= $${{\left( {10 - 5} \right) \times {{10}^{ - 3}}} \over {\left( {200 - 100} \right) \times {{10}^{ - 6}}}}$$ = 50
3
MCQ (Single Correct Answer)

AIPMT 2009

The symbolic representation of four logic gates are given below



The logic symbols for OR, NOT and NAND gates are respectively
A
(iv), (i), (iii)
B
(iv), (ii), (i)
C
(i), (iii), (iv)
D
(iii), (iv), (ii)

Explanation

OR gate, NOT gate and NAND gates are (iv), (ii) and (i) respectively.
4
MCQ (Single Correct Answer)

AIPMT 2008

If the lattice parameter for a crystalline structure is 3.6 $$\mathop A\limits^ \circ $$, then the atomic radius in fcc crystal is
A
2.92 $$\mathop A\limits^ \circ $$
B
1.27 $$\mathop A\limits^ \circ $$
C
1.81 $$\mathop A\limits^ \circ $$
D
2.10 $$\mathop A\limits^ \circ $$

Explanation

The atomic radius in a f.c.c. crystal is = $${a \over {2\sqrt 2 }}$$

$$ \therefore $$ Atomic radius = $${{3.6} \over {2\sqrt 2 }}$$ = 1.27 $$\mathop A\limits^ \circ $$

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