Valve Electronics Test

Result

Valve Electronics Test - 4

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Weekly Quiz Competition

Question 1
1 / -0

Thermionic emission from a heated filament varies with its temperature T as

A
T⁻¹

B
T

C
T²

D
T^3/2

Solution

According to Richardson-Dushman equation, number of thermions emitted per sec per unit area J = AT⁻²e^−W0/kT ⇒ J ∝ T²
Question 2
1 / -0

Due to S.C.R in vacuum tube

A
I_p→ Decreases

B
I_p→ Increases

C
V_p→Increases

D
V_g →Increases

Solution

In SCR (Space charge region) electrons collect around the plate, this cloud decreases the emission of electrons from the cathode, hence plate current decreases.
Question 3
1 / -0

In a triode, gm = 2×10⁻³ohm⁻¹,μ = 42, resistance load, R = 50 kilo ohm. The voltage amplification obtained from this triode will be

A
30.42

B
29.57

C
28.18

D
27.15

Solution
Question 4
1 / -0

In an amplifier the load resistance R_L is equal to the plate resistance (r_β). The voltage amplification is equal to

A
μ

B
2μ

C
μ/2

D
μ/4

Solution
Question 5
1 / -0

If R_p = 7kω , gm = 2.5 millimho , then on increasing plate voltage by 50V, how much the grid voltage is changed so that plate current remains the same?

A
−2.86V

B
−4V

C
+4V

D
+2V

Solution
Question 6
1 / -0

In a triode amplifier, μ = 25,r_p =40 kilo ohm and load resistance R_L=10 kilo ohm. If the input signal voltage is 0.5 volt, when output signal voltage will be

A
1.25 volt

B
5 volt

C
2.5 volt

D
10 volt

Solution
Question 7
1 / -0

The amplification factor of a triode is 20. If the grid potential is reduced by 0.2 volt then keep the plate current constant its plate voltage is to be increased by

A
10 volt

B
4 volt

C
40 volt

D
100 volt

Solution

Given:-

Amplification factor = 20

Reduction in grid potential = 0.2V

From the formulae, we know that
Question 8
1 / -0

For a triode r_p= 10 kilo ohm and gm = 3 milli mho If the loads resistance is double of plate resistance, then the value of voltage gain will be

A
10

B
20

C
15

D
30

Solution
Question 9
1 / -0

In an experiment, the saturation in the plate current in a diode is observed at 240 V. But a student still wants to increase the plate current. It can done, if

A
The plate voltage is increased further

B
The plate voltage is decreased

C
The filament current is decreased

D
The filament current is increased

Solution

After saturation plate current can be increased by increasing the temperature of filament. It can be done by increasing the filament current.
Question 10
1 / -0

For a given triode μ=20. The load resistance is 1.5 times the anode resistance. The maximum gain will be

A
16

B
12

C
14

D
None of the above

Solution