# NTA (UGC)-NET: Physics MCQs (Practice_Test 9 of 35)

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1. An electron having kinetic energy T is moving in a circular orbit of radius R perpendicular to a uniform Magnetic induction B. If kinetic energy is doubled and magnetic induction is tripled, The radius will become

1. R '9/4

2. R '3/2

3. R '2/9

4. R '4/3

2. If in the first Bohr orbit of a hydrogen atom the total energy of the electron is-21.76 × 10 − 19 J, then its potential energy will be

1. -43.52 × 10 − 19 J

2. -21.76 × 10 − 19 J

3. -10.88 × 10 − 19 J

4. -13.60 × 10 − 19 J

3. Consider the following substances, which are frequently used as a source of electrons:

1. Magnesium

2. Calcium

3. Tungsten

4. Platinum

The correct sequence of the above substances in increasing order of their work functions is

1. 1, 2, 3, 4

2. 2, 1, 3, 4

3. 2, 1, 4, 3

4. 1, 2, 4, 3

4. The de-Broglie wavelength of material particles which are in thermal equilibrium at temperature T is

1. h/sqrt 2mkT

2. h/sqrt 2 mkT

3. h-mkT

4. h/sqrt2 kT

5. The phase velocity (Vp) and the group velocity (Vg) of a de-Broglie wave, in free space (speed of light is c) are related as

1. Vp/Vg = sqrt2

2. Vp. Vg = C2

3. Vp/Vg = 0.5

4. Vp Vg = 2C2

6. In Compton scattering, the incident photon will lose maximum energy if it is scattered at an angle of:

1. 0

2. 60

3. 90

4. 180

7. In one of the radioactive decay chains we come across the element 22688 Ra. The final product of the chain is 20682 Pb. The number of a and b-is emitted

1. 3 a and 6b-

2. 4 a and 5b-

3. 5 a and 4b-

4. 6 a and 6b-

8. At time t. = 0, N1 nuclei of decay constant l1 and N2 nuclei of decay constant l2 are mixed. The decay rate of the mixture is

1. N1 N2 e- (l1 + l2) t

2. (N1/N2) e- (l1 − l2) t

3. (N1 N2 e-l1t + N2 l2 e-l 2t)

4. N1/N2 e- (l1 + l2) t

9. The nuclear reaction is an example of

1. nuclear chain reaction

2. successive disintegration

3. pair production

4. artificial radioactivity

10. Which one of the following particles is a lepton?

1. Neutron

2. Proton

3. Electron

4. Lambda

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

 List-I (Process) List-II (Approximate Energy released in mV) Fission of one uranium nucleusFormation of one helium nucleus by FissionFormation of a compound nucleusFormation of a deuteron by the Energy 2Energy 8Energy 200 by the capture of a neutronEnergy 28 captures of a neutron by a proton
• A
• B
• C
• D
• 3
• 4
• 2
• 1
• 2
• 4
• 1
• 3
• 4
• 2
• 3
• 1
• 3
• 1
• 2
• 4
12. Under space charge condition with the plate voltage Eb = 100 V and the permanence K = 104 (In S. I unit), the plate current in a diode will be

1. 10 − 6 mA

2. 10 mA

3. 102 mA

4. 106 mA

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