# Competitive Exams: Physics MCQs (Practice-Test 4 of 35)

1. For the following nuclear fusion reaction in a stellar system e + energy

1. only very high temperature is required

2. normal temperature and very high pressure are required

3. very high temperature and comparatively high pressure are required

4. very high temperature and very low pressure are required

2. If the mass of neutron = 1.7 × 10 − 27 kg, then the de-Broglie wavelength of neutron of energy 3 eV is

1. 0.14 × 10 − 11 m

2. 0.14 × 10 − 10 m

3. 1.4 × 10 − 10 m

4. 1.4 × 108 m

3. The proper mean-life of a Muon is 2.2 × 10 − 6, s: If it is travelling at a speed of 0.8 c, its lifetime will be

1. 3.66 microseconds

2. 2.75 micro seconds

3. 2.20 micro seconds

4. 1.32 micro seconds

4. Consider the following statements regarding “Hadrons”

1. Mesons and Baryons are together known as Hadrons

2. Only Baryons are known as Hadrons

Which of the above statement (s) is/are correct?

1. 1 alone

2. 2 alone

3. 2 and 3

4. 1 and 3

5. Match List I with List II and select the correct answer:

 List-I (Principle) List-II (Process) Conservation of charges Conservation of energy Violation of Parity Conservation of momentum Neutrino in beta decay Weak interactions Pair production in the vicinity of a nucleus Annihilation of electron and positron
• A
• B
• C
• D
• 4
• 1
• 3
• 2
• 1
• 3
• 2
• 4
• 4
• 1
• 2
• 3
• 2
• 4
• 1
• 3
6. Consider the following events:

1. Positive voltage on the anode pulling the electrons

2. Heating the emitter (cathode)

3. Electrons passing the potential minimum near the cathode due to space charge

4. Secondary electrons

The correct sequence in which these events occur inside an operating diode (valve) is

1. 1, 2, 3, 4

2. 2, 1, 3, 4

3. 2, 3, 4, 1

4. 4, 2, 3, 1

7. The anode current in a triode valve is given by if VA = 300 V, then the minimum negative value of grid bias voltage required to cut off the valve will be

1. 10 V

2. 103/2 V

3. 10 × 103/2 V

4. 100 V

8. Above figure shows a half-wave rectifier with resistive load RL, which is far greater than the diode forward resistance. If the value of capacitor C is considerably large, then the do voltage across R1 is

1. 10 V

4. 28 V

9. If the barrier potential changes with biasing of a p-n junction diode, then the barrier potential will

1. increase with both reverse and forward bias

2. decrease with both reverse and forward bias

3. increase with forward bias and decrease with reverse bias

4. increase with reverse bias and decrease with forward bias

10. The mutual characteristic of a triode is shown in the above figure for operating point Q specified by VA = 200 V, VG = -4 V and IA = 10 mA. If the anode slope resistance? p = 10 k? then the amplification factor p will be

1. (3/2) 10 − 6

2. (3/2) 10 − 3

3. 15

4. (⅔) 103

11. Match List I with List II and select the correct answer:

 List-I (Device) List-II (Important Property) P-N diode Vaccum diode Triode BJT Current amplification Three different circuit configurations possible Rectification Avalanche breadown
• A
• B
• C
• D
• 4
• 3
• 2
• 1
• 4
• 3
• 1
• 2
• 3
• 1
• 2
• 4
• 2
• 3
• 4
• 1
12. When a transistor amplifier having current gain of 75 is given an input signal v i = 2sin [157 t +?/2 ] the output signal is found to be v 0 = 200 sin [157 t + 3]? The transistor is connected as 2

1. a common collector amplifier

2. a common base amplifier

3. a common emitter amplifier

4. an oscillator

13. Match List I with List II, in respect of a BJT connected in the CE configuration and select the correct answer:

 List-I (Characteristics) List-II (Properties) Power gain Voltage gain Phase change between I/O Input impedance Lowest Yes Low High Highest
• A
• B
• C
• D
• 3
• 4
• 5
• 2
• 5
• 4
• 2
• 3
• 5
• 3
• 2
• 4
• 4
• 2
• 1
• 3
14. The circuit diagram of a common emitter amplifier using a silicon transistor with hFE = 100 is shown in the above figure. It is operated at VCE = 8 V. IC = 2 mA In this circuit RB. In k? will be

1. 7.2

2. 7.5

3. 720

4. 750

15. Radiocarbon is produced in the atmosphere as a result of

1. collision between fast neutrons and nitrogen nuclei present in the atmosphere

2. action of ultraviolet light from the sun on atmospheric oxygen

3. action of solar radiations particularly cosmic rays on carbon dioxide present in the atmosphere

4. lightning discharge in atmosphere

16. Figure I shows a logic gate circuit with two inputs A and B and the output C. The voltage waveforms of A, B and C are shown in figure II. The logic circuit is

1. OR gate

2. AND gate

3. NAND gate

4. NOR gate

17. Figure I shows a two-input type of logic circuit where A and IS are the inputs and C is the output. The truth table of the logic gate is give in figure It. The logic gate is

1. AND

2. OR

3. NOR

4. NAND

18. If the output of a logic gate is 0 when all its inputs are at logic 1, then the gate is either

1. NAND or Ex-NOR

2. NOR or OR

3. Ex-OR or NOR

4. AND or NOR

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