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21. (JEE Main 2019 (Online) 9th January Evening Slot)

Ge and Si diodes start conducting at 0.3 V and 0.7 V respectively. In the following figure if Ge diode connection are reversed, the value of V0 changes by : (assume that the Ge diode has large breakdown voltage)

JEE Main 2019 (Online) 9th January Evening Slot Physics - Semiconductor Question 133 English

A. 0.8 V

B. 0.6 V

C. 0.2 V

D. 0.4 V

The Correct Answer is Option (D)

Case 1 :
JEE Main 2019 (Online) 9th January Evening Slot Physics - Semiconductor Question 133 English Explanation 1
Ge need 0.3 V for start conducting and Si need 0.7 V for start conducting.

So, conduction will be start by Ge.

Out of 12 V, 0.3V will be consumed by Ge.

  V01 = 12 0.3 = 11.7 V

Case 2 :
JEE Main 2019 (Online) 9th January Evening Slot Physics - Semiconductor Question 133 English Explanation 2
Here as Ge diode is in reverse bias so no conduction will happen through Ge diode

As Si diode is in forward bias so conduction will happen through Si diode.

Here Si diode consume 0.7 V.

So, V02 = 12 0.7 = 11.3 V

  Value of V0 changes by

= 11.7 11.3 = 0.4 V

22. (JEE Main 2018 (Offline))

The reading of the ammeter for a silicon diode in the given circuit is : JEE Main 2018 (Offline) Physics - Semiconductor Question 148 English

A. 13.5 mA

B. 0

C. 15 mA

D. 11.5 mA

The Correct Answer is Option (D)

Note

From the circuit you can see the diode is in forward bias, and to start current flow through the circuit. Accross silicon diode the voltage drop should be 0.7 V and for Germenium diode the voltage drop is 0.3 V. Then diode will start working and current will flow through the circuit.

So, the net voltage available accros the registor is (Vnet) = 3 0.7 = 2.3 V

Current flow through circuit = 2.3 200 = 11.5 mA

23. (JEE Main 2013 (Offline))

A diode detector is used to detect an amplitude modulated wave of 60 % modulation by using a condenser of capacity 250 picofarad in parallel with a load resistance 100 kilo o h m . Find the maximum modulated frequency which could be detected by it. JEE Main 2013 (Offline) Physics - Semiconductor Question 166 English

A. //--> 10.62

B. //--> 10.62

C. //--> 5.31

D. //--> 5.31

The Correct Answer is Option (B)

Given : Resistance R = 100 kilo o h m = 100 × 10 3 Ω

Capacitance C = 250 picofarad = 250 × 10 12 F

τ = R C = 100 × 10 3 × 250 × 10 12 sec

= 2.5 × 10 7 × 10 12 sec

= 2.5 × 10 5 sec

The higher frequency which can be detected with tolerable distortion is

f = 1 2 π m a R C

= 1 2 π × 0.6 × 2.5 × 10 5 H z

= 100 × 10 4 2.5 × 1.2 π H z

= 10.61 K H z

This condition is obtained by applying the condition that rate of decay of capacitor voltage must be equal or less than the rate of decay modulated signal voltage for proper detection of modulated signal.

24. (AIEEE 2007)

If in a p - n junction diode, a square input signal of 10 V is applied as shown

AIEEE 2007 Physics - Semiconductor Question 158 English

Then the output signal across R L will be

A. AIEEE 2007 Physics - Semiconductor Question 158 English Option 1

B. AIEEE 2007 Physics - Semiconductor Question 158 English Option 2

C. AIEEE 2007 Physics - Semiconductor Question 158 English Option 3

D. AIEEE 2007 Physics - Semiconductor Question 158 English Option 4

The Correct Answer is Option (A)

The current will flow through R L when the diode is forward biased.

25. (AIEEE 2006)

The circuit has two oppositively connected ideal diodes in parallel. What is the current following in the circuit?

AIEEE 2006 Physics - Semiconductor Question 161 English

A. 1.71 A

B. 2.00 A

C. 2.31 A

D. 1.33 A

The Correct Answer is Option (B )

D 2 is forward biased whereas D 1 is reversed biased.

So effective resistance of the circuit

R = 4 + 2 = 6 Ω

i = 12 6 = 2 A