1

### 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)

A
0.8 V
B
0.6 V
C
0.2 V
D
0.4 V

## Explanation

Case 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.

$\therefore$  V01 = 12 $-$ 0.3 = 11.7 V

Case 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

$\therefore$  Value of V0 changes by

= 11.7 $-$ 11.3 = 0.4 V
2

### JEE Main 2019 (Online) 10th January Morning Slot

To get output 1 at R, for the given logic gate circuit the input values must be

A
x = 0,  y = 0
B
x = 1,  y = 0
C
x = 0,  y = 1
D
x = 1,  y = 1

## Explanation

P = $\overline x +$ y

Q = $\overline {\overline y .x}$ = y + $\overline x$

Output, R = $\overline {P + Q}$

To make R = 1

$\overline {P + Q}$ should be = 1

$\therefore$ P + Q must be 0

$\therefore$ ($\overline x +$ y) + (y + $\overline x$) = 0

Now by checking each option you can see

When y = 0 and x = 1 then

$\overline x +$ y = 0

$\therefore$ ($\overline x +$ y) + (y + $\overline x$) = 0
3

### JEE Main 2019 (Online) 10th January Evening Slot

For the circuit shown below, the current through the Zener diode is -

A
5 mA
B
zero
C
14 mA
D
9 mA

## Explanation

Assuming zener diode doesnot undergo breakdown, current in circuit

= ${{120} \over {15000}}$ = 8mA

$\therefore$  Voltage drop across diode

= 80 V > 50 V.

The diode undergo breakdown.

Current is R1 = ${{70} \over {5000}}$ = 14mA

Current is R2 = ${{50} \over {10000}}$ = 5mA

$\therefore$  Current through diode = 9mA
4

### JEE Main 2019 (Online) 11th January Morning Slot

In the given circuit the current through Zener Diode is close to:

A
0.0 mA
B
6.7 mA
C
4.0 mA
D
6.0 mA

## Explanation

Since voltage across zener diode must be less than 10V therefore it will not work in breakdown region, & its resistance will be infinite & current through it = 0

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