Semiconductor Electronics: Materials, Devices and Simple Circuits Test 44

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Semiconductor Electronics: Materials, Devices and Simple Circuits Test 44

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Question 1
1 / -0

Zener diodes with breakdown voltage ranging over 2V- 200 V are commercially available. Breakdown voltage of a zener diode

A
Increases with increasing doping concentration

B
Decreases with increasing doping concentration

C
Does not depend on doping concentration

D
May increases or decreases with increasing doping concentration

Solution

For Zener Diodes, the breakdown voltage decreases with increasing doping concentration.
Question 2
1 / -0

In a p-n junction diode, not connected to any circuit

A
The potential is the same everywhere

B
The p-type side is at a higher potential than the n-type side

C
There is an electric field at the junction directed from the n-type side to the p-type side

D
There is an electric field at the junction directed from the p-type side to the n-type side

Solution

In pn function diode p side of diode (+ve side) attract $-ve$ charge and due to induct ion opposite charge $+ve$ charge appraises on n side which produce potential barrierand we know that charge separation produce electric fields from inside to p side of diode.
Question 3
1 / -0

Which of the following is a correct statement about current carrying conductor?

A
On increasing temperature drifts speed of free electron decreases

B
On increasing temperature drift speed of free electron increases

C
On increasing temperature, drift speed of free electron remains same.

D
On increasing P.D. average kinetic energy of electron decreases ( Neglected heating effect of electric current)

Solution

$vd =\dfrac{et}{m} E$
$t \downarrow$ as $T \uparrow ]$
As the temperature increases, the thermal agitation of the electrons increases thereby, increasing the number of collisions. Hence, drift velocity of the electrons decreases.
Question 4
1 / -0

In the circuit shown in figure, the diode is ideal. The potential difference between A and B is?

A
$V/4$

B
V

C
Zero

D
$V/2$

Solution

Diode short circuits the resistance of $2\Omega$ .
$\therefore$ Voltage across points A and B will be
$V_1=\dfrac{\dfrac{2}{3}}{\dfrac{2}{3}+2}\times V=\dfrac{V}{4}$ .
Question 5
1 / -0

The following figure shown a logic gate circuit with two input A and B output C. The voltage waveforms of A, B and C are as shown in second figure given. The logic gate is?

A
OR gate

B
AND gate

C
NAND gate

D
NOR gate

Solution

Let's make truth table first,
See the image
The above truth table is of 'OR' gate.
Question 6
1 / -0

Read the following diagram and tell which of the following statements are true:

A
In circuit 1 lamp does not glow but in circuit 2 lamp glows

B
In circuit 1 as well as 2 lamp does not glow

C
In circuit 1 lamp glows but in 2 lamp does not glow

D
In both circuit lamp glows

Solution

In (i) circuit, the emitter base junction is not biased, so no current flows across L; hence lamp L does not light. In (ii) circuit, the emitter base junction is forward biased, so emitter and hence collector current flows and lamp L lights up.
Question 7
1 / -0

Germanium and silicon junction diodes are connected in parallel. These are connected in series with a resistance $R$ , a milliammeter $(mA)$ and a key $(K)$ as shown in Fig. When key $(K)$ is closed a current begins to flow in the milliammeter. The potential drop across the germanium diode is then

A
$0.3 V$

B
$0.7 V$

C
$1.1 V$

D
$12 V$

Solution

In Fig. germanium diode is reverse biased and silicon diode is forward biased. Therefore, there will be no current in the branch of germanium diode. The potential barrier of silicon diode is $0.7 V$ . Therefore, for conduction minimum potential difference across silicon is $0.7 V$ .
Maximum potential difference across resistance, $R = 12 - 0.7 = 11.3 V.$
Question 8
1 / -0

For the plate voltage, the plate current in a triode valve is maximum when the potential of :

A
The gird is positive and plate is negative

B
The grid is zero and plate is positive

C
The grid is negative and plate is positive

D
The grid is positive and plate is positive

Solution

When grid is given potential more electrons will cross the grid to reach the positive plate $p$ . Hence current increases.
Question 9
1 / -0

The electrical conductivity of a semiconductor increases when emf radiation of wavelength shorter the $2480$ nm is incident in it. The band gap (in eV) for the semiconductor is?

A
$0.9$

B
$0.7$

C
$0.5$

D
$1.1$

Solution
Question 10
1 / -0

A non-conducting device is connected in a series circuit with a battery and a resistance. A current is found to pass through the circuit. If the polarity of the battery is reversed, the current drops to almost zero. The device may be

A
a p-n junction diode

B
an intrinsic semiconductor

C
a p-type semiconductor

D
a n-type semiconductor

Solution

This behavior can be shown by a p-n junction.
In the previous polarity, the p-n junction will be forward biased and so allowing to pass current through it. After reversing the polarity, it will be in reverse bias so won't allow current to pass through it.