Physics M.C.Q (1 Marks)

The grid in a triode valve is used(a) To increases the thermionic emission(b) To control the plate to cathode current(c) To reduce the inter-electrode capacity(d) To keep cathode at constant potential

Current in the circuit will be

The typical ionisation energy of a donor in silicon is(a) 10.0 eV(b) 1.0eV(c) 0.1 eV(d) 0.001 eV

The probability of electrons to be found in the conduction band of an intrinsic semiconductor at a finite temperature(a) Decreases exponentially with increasing band gap(b) Increases exponentially with increasing band gap(c) Decreases with increasing temperature (d) Is independent of the temperature and the band gap

Select the correct statement(a) In a full wave rectifier, two diodes work alternately (b) In a full wave rectifier, two diodes work simultaneously(c) The efficiency of full wave and half wave rectifiers is same(d) The full wave rectifier is bi-directional

Plate voltage of a triode is increased from 200 V to 225 V. To maintain the plate current, change in grid voltage from 5V to 5.75 V is needed. The amplification factor is (a) 40(b) 45(c) 33.3(d) 25

In a diode valve the cathode temperature must be (f = work function)(a) High and ∅  should be high(b) High and ∅ should be low(c) Low and ∅ should be high(d) Low and ∅ should be high

The ripple factor in a half wave rectifier is(a) 1.21(b) 0.48(c) 0.6(d) None of these

The transconductance of a triode amplifier is 2.5 mili mho having plate resistance of 20 KW, amplification 10. Find the load resistance(a) 5 kW  (b) 25 kW(c) 20 kW(d) 50 kW

The amplification factor of a triode is 50. If the grid potential is decreased by 0.20 V, what increase in plate potential will keep the plate current unchanged(a) 5 V(b) 10 V(c) 0.2 V(d) 50 V

The thermionic emission of electron is due to(a) Electromagnetic field(b) Electrostatic field(c) High temperature(d) Photoelectric effect

The voltage gain of a triode depends upon(a) Filament voltage(b) Plate voltage(c) Plate resistance(d) Plate current

The electrical circuits used to get smooth d.c. output from a rectifier circuit is called(a) Filter(b) Amplifier(c) Full wave rectifier(d) Oscillator

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) 10       (d) None of the above

Diode is used as a/an(a) Oscillator(b) Amplifier(c) Rectifier(d) Modulator

In a diode valve, the state of saturation can be obtained easily by(a) High plate voltage and high filament current(b) Low filament current and high plate voltage(c) Low plate voltage and high cathode temperature(d) High filament current and high plate voltage

Which one is correct relation for thermionic emission

Coating of strontium oxide on Tungsten cathode in a valve is good for thermionic emission because(a) Work function decreases(b) Work function increases(c) Conductivity of cathode increases(d) Cathode can be heated to high temperature

The introduction of a grid in a triode valve affects plate current by (a) Making the thermionic emission easier at low temperature(b) Releasing more electrons from the plate(c) By increasing plate voltage(d) By neutralising space charge

With a change of load resistance of a triode, used as an amplifier, from 50 kilo ohms to 100 kilo ohms, its voltage amplification changes from 25 to 30. Plate resistance of the triode is(a) 25 kW(b) 75 kW(c) 7.5 kW(d) 2.5 kW

The unit of mutual conductance of a triode valve is

The triode constant is out of the following(a) Plate resistance(b) Amplification factor(c) Mutual conductance(d) All the above

In the circuit of a triode valve, there is no change in the plate current, when the plate potential is increased from 200 volt to 220 volt and the grid potential is decreased from – 0.5 volt to –1.3 volt. The amplification factor of this valve is(a) 15(b) 20(c) 25 (d) 35

The amplification factor of a triode valve is 15. If the grid voltage is changed by 0.3 volt the change in plate voltage in order to keep the plate current constant (in volt) is (a) 0.02(b) 0.002(c) 4.5(d) 5.0

In a triode valve (a) If the grid voltage is zero then plate current will be zero(b) If the temperature of filament is doubled, then the thermionic current will also be doubled(c) If the temperature of filament is doubled, then the thermionic current will nearly be four times(d) At a definite grid voltage the plate current varies with plate voltage according to Ohm’s law

The combination of the gates shown in the figure below produces

In a triode amplifier, the value of maximum gain is equal to(a) Half the amplification factor      (b) Amplification factor(c) Twice the amplification factor(d) Infinity

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

The amplification produced by a triode is due to the action of(a) Filament(b) Cathode(c) Grid   (d) Plate

The amplification factor of a triode is 20. If the grid potential is reduced by 0.2 volt then to 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

Number of secondary electrons emitted per number of primary electrons depends on(a) Material of target(b) Frequency of primary electrons(c) Intensity(d) None of the above