Subject

Physics

Class

CBSE Class 12

Pre Boards

Practice to excel and get familiar with the paper pattern and the type of questions. Check you answers with answer keys provided.

Sample Papers

Download the PDF Sample Papers Free for off line practice and view the Solutions online.
Advertisement

 Multiple Choice QuestionsShort Answer Type

21.

How does one explain the emission of electrons from a photosensitive surface with the help of Einstein's photoelectric equation?

 

6871 Views

Advertisement

22.

The work function of the following metals is given : Na 2.75 ev, K = 2.3 eV, Mo = 4.17 eV and Ni = 5.15 eV. Which of these metals will not cause photoelectric emission for radiation of wavelength 3300 Å from a laser source placed 1 m away from these metals? What happens if the laser source is brought nearer and placed 50 cm away?


straight E space equals space hc over straight lambda space equals space fraction numerator 6.63 space straight x 10 to the power of negative 34 end exponent space straight x space 3 space straight x space 10 to the power of 8 over denominator 3.3 space straight x space 10 to the power of negative 7 end exponent space straight x 1.6 space straight x 10 to the power of negative 19 end exponent end fraction eV
space equals space 3.77 space eV

The work function of Mo and Ni is more than the energy of the incident
photons; so photoelectric emission will not take place from these metals.
Kinetic energy of photo electrons will not change, only photoelectric current
will change.

1710 Views

Advertisement
23.

Define the term 'amplitude modulation'. Explain any two factors which justify the need for modulating a low-frequency base band signal.

1926 Views

24.

A radioactive nucleus 'A' undergoes a series of decays as given below:
straight A space rightwards arrow with straight alpha on top space straight A subscript 1 space rightwards arrow with straight beta on top space straight A subscript 2 space rightwards arrow with straight alpha on top space straight A subscript 3 space rightwards arrow with straight gamma on top space straight A subscript 4
The mass number and atomic number of A2 are 176 and 71 respectively. Determine the mass and atomic number of A4 and A.

1621 Views

Advertisement
25.

Write the basic nuclear process underlying β+ and β- decays.

1545 Views

26.

For a CE-transistor amplifier, the audio signal voltage across the collector resistance of 2 kΩ is 2 V. Given the current amplification factor of the transistor is 100, find the input signal voltage and base current, if the base resistance is 1 kΩ. 

1431 Views

27.

Mrs Rashmi Singh broke her reading glasses. When she went to the shopkeeper to order new specs, he suggested that she should get spectacles with plastic lenses instead of glass lenses. On getting the new spectacles, she found that the new ones were thicker than the earlier ones. She asked this question to the shopkeeper but he could not offer a satisfactory explanation for this. At home, Mrs Singh raised the same question to her daughter Anuja who explained why plastic lenses were thicker.

(a) Write two qualities displayed each by Anuja and her mother.

(b) How do you explain this fact using lens maker's formula?

2137 Views

28.

A narrow beam of unpolarized light of intensity I0 is incident on a Polaroid P1. The light transmitted by it is then incident on a second polaroid P2 with its pass axis making the angle of 60° relatives to the pass axis of P1. Find the intensity of the light transmitted by P2.

1726 Views

Advertisement
29.

Explain two features to distinguish between the interference pattern in Young's double slit experiment with the diffraction pattern obtained due to a single slit.

1467 Views

30.
A monochromatic light of wavelength 500 nm is incident normally on a single slit of width 0.2 mm to produce a diffraction pattern. Find the angular width of the central maximum obtained on the screen.

Estimate the number of fringes obtained in Young's double slit experiment with fringe width 0.5 mm, which can be accommodated within the region of the total angular spread of the central maximum due to the single slit.
2890 Views

Advertisement