The junction diode in the following circuit requires a minimum current of 1 mA to be above the knee point (0.7 V) of its I-V characteristic curve. The voltage across the diode is independent of current above the knee point. If ${\mathrm{V}}_{\mathrm{B}}$ = 5 V, then the maximum value of R so that the voltage is above the knee point, will be

(1) 4.3 k$\mathrm{\Omega }$                

(2) 860 k$\mathrm{\Omega }$

(3) 4.3 $\mathrm{\Omega }$                  

(4) 860 $\mathrm{\Omega }$

In the circuit given below, V(t) is the sinusoidal voltage source, voltage drop ${\mathrm{V}}_{\mathrm{AB}}$(t) across the resistance R is

(1) Is half wave rectified

(2) Is full wave rectified

(3) Has the same peak value in the positive and negative half cycles

(4) Has different peak values during positive and negative half cycle

The peak voltage in the output of a half-wave diode rectifier fed with a sinusoidal signal without filter is 10 V. The dc component of the output voltage is 
(1)$10/\sqrt{2}$  V                                   

(2) $10/\mathrm{\pi }$ V

(3) 10 V                                           

(4) $20/\mathrm{\pi }$ V

A transistor is used as an amplifier in CB mode with a load resistance of 5 k$\mathrm{\Omega }$. The current gain of the amplifier is 0.98 and the input resistance is 70 $\mathrm{\Omega }$, the voltage gain and power gain respectively are :
(1) 70, 68.6                         

(2) 80, 75.6

(3) 60, 66.6                         

(4) 90, 96.6

The Bohr radius of the fifth electron of phosphorus (atomic number = 15) acting as dopant in silicon (relative dielectric constant = 12) is
(a) 10.6 Å                (b) 0.53 Å
(c) 21.2 Å                (d) None of these

In the following circuits PN-junction diodes ${\mathrm{D}}_1$, ${\mathrm{D}}_2$ and ${\mathrm{D}}_3$ are ideal for the following potential of A and B, the correct increasing order of resistance between A and B will be

(i) – 10 V, – 5V           (ii) – 5V, – 10 V
(iii) – 4V, – 12V

(a) (i) < (ii) < (iii)                       (b) (iii) < (ii) < (i)
(c) (ii) = (iii) < (i)                       (d) (i) = (iii) < (ii)

The circuit shown in the following figure contains two diode ${\mathrm{D}}_1$ and ${\mathrm{D}}_2$ each with a forward resistance of 50 ohms and with infinite backward resistance. If the battery voltage is 6 V, the current through the 100 ohm resistance (in amperes) is

1.  Zero 
2.  0.02
3.  0.03 
4.  0.036

The contribution in the total current flowing through a semiconductor due to electrons and holes are $\frac{3}{4}$ and $\frac{1}{4}$ respectively. If the drift velocity of electrons is $\frac{5}{2}$ times that of holes at this temperature, then the ratio of concentration of electrons and holes is
1. 6 : 5                 

2. 5 : 6

3. 3 : 2                 

4. 2 : 3

Ge and Si diodes conduct at 0.3 V and 0.7 V respectively. In the following figure if Ge diode connection are reversed, the valve of ${\mathrm{V}}_0$ changes by 

(1) 0.2 V                   

(2) 0.4 V

(3) 0.6 V                   

(4) 0.8 V

In the circuit shown in the figure, the maximum output voltage ${\mathrm{V}}_0$ is :

1. 0 V                        2. 5 V
3. 10 V                      4. $\frac{5}{\sqrt{2}}$