Semiconductor Electronics: Materials, Devices and Simple Circuits Test 45

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Semiconductor Electronics: Materials, Devices and Simple Circuits Test 45

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Question 1
1 / -0

Consider two $$npn$$ transistors as shown in figure. If $$0$$ volts corresponds to false and $$5$$ volts correspond to true then the output at $$C$$ correspond to true then the output at $$C$$ corresponds to:

A
$$A\ NAND\ B$$

B
$$A\ OR\ B$$

C
$$A$$ and $$B$$

D
$$A\ NOR\ B$$

Solution

There are two individual NOT gates and when they combine they form a NAND gate.
Question 2
1 / -0

The I -V characteristic of an LED is:

A

B

C

D

Solution

LED is working only in forward biased condition. $$\therefore I-V$$ characteristics will be forward$$I-V$$ characteristics of a diode. therefore option D is correct.
Question 3
1 / -0

The impurity atoms needed to make a p-type semiconductor are

A
phosphorus

B
boron

C
antimony

D
arsenic

Solution

According to theory,
p- type semiconductor has holes as a majority charge carrier,
or in short they lack electrons,

Such semiconductors can be made by adding 13 group elements which
lacks an electron,

In the given options,
Only boron is of 13 group, and hence adding boron as an impurity,

Semiconductor becomes p-type.
Question 4
1 / -0

The dominant mechanisms for motion of charge carriers in forward and reversed biased silicon p-n junctions are :

A
Diffusion in forward bias, drift in reverse bias

B
Diffusion in both forward and reverse bias

C
Drift in both forward and reverse bias

D
None of these

Solution

$$\Rightarrow $$ In forward bias we apply voltage in a direction opposite to that of barrier potential p-side to positive terminal, n-side to negative terminal of battery. So electrons in the n-side, holes in p side pushed towards the junction. Results in increased diffusion.
$$\Rightarrow $$ In reverse bias, electrons in n-side, holes in p-side pushed away from function.
Ref. image

n-side to positive terminal p-side to negative terminal.
Question 5
1 / -0

In the depletion layer, the electric field created

A
is from n-side to p-side

B
is from p-side to n-side

C
changes randomly

D
depends on the biasing

Solution

Because of diffusion a layer of holes is formed over N-side and a layer of electron is formed over P-side as shown below.
Now, as we see the direction of $$\vec { E } $$ is form $$N$$ to $$P$$.
$$\Rightarrow$$ Option (A) is the correct answer.
Question 6
1 / -0

Which of the following circuits correctly represents the following truth table?

A

B

C

D

Solution
Question 7
1 / -0

The dominant mechanisms of motion of change carriers in forward and reverse biased silicon $$P-N$$ junction are

A
drift in forward bias, diffusion in reverse bias

B
diffusion in forward bias, drift in reverses bias

C
diffusion in both forward and reverse bias

D
drift in both forward and reverse bias

Solution

In forward bias we apply voltage in a direction opposite to that of the barrier potential. Now, we know that the p-side of the diode is connected to the positive terminal and the n-side of the diode is connected to the negative terminal of the battery.

So, the electrons in the n-side and the holes in the p-side get pushed towards the junction. This results in increased diffusion of electrons from n-side to p-side region and the increased diffusion of holes from p-side to n-side region. Hence, dominant mechanism in forward bias is due to diffusion.

In reverse bias, the n-side of the diode is connected to the positive terminal and the p-side is connected to the negative terminal.
So, the electrons in the n-side and the holes in the p-side get pushed away from the junction. This results in zero diffusion current. Hence, dominant mechanism in reverse bias is due to drift.

So, the correct answer is option 3.
Question 8
1 / -0

In which of the following circuits is the diode forward biased?

A

B

C

D

Solution

Here,
The pointed part of the triangle in the diode symbol is n type and the other is p type,

Diode conducts in forward bias,
And forward bias means high voltage on p-type and low voltage on the n-type,

In all the above options,

Only option $$D$$ has high voltage on p-side and low voltage on low side.
Question 9
1 / -0

A zener regulated power supply consists of a $$9 V $$ battery connected in series with a and a zener diode. The zener diode maintains a constant voltage drop of $$4V $$ The current drawn by the load resistance will be :

A
$$0.025 A$$

B
$$0.050 A$$

C
$$0.01 A$$

D
$$0.015 A$$
Question 10
1 / -0

If the resistivity of an alloy is $$\rho '$$ and that of constituent metal is $$\rho $$ then :

A
$$\rho ' > \rho $$

B
$$\rho ' < \rho $$

C
$$\rho ' = \rho $$

D
there is no simple reaction between $$\rho '\& \rho $$

Solution

Usually alloys have higher resistivity then pure metals. The different atoms in the alloy cause the electrons to have more interruptions and scattering in their otherwise smooth flow.