21.

Identify the logic gates marked 'P' and 'Q' in the given circuit. Write the truth table for the combination.

22.

A proton and a deuteron are accelerated through the same accelerating potential. Which one of the two has
(a) greater value of de-Broglie wavelength associated with it, and

(b) less momentum?

Give reasons to justify your answer.

23.

(i) Monochromatic light of frequency 6.0 × 10¹⁴ Hz is produced by a laser. The power emitted is 2.0 × 10⁻³ W. Estimate the number of photons emitted per second on an average by the source. 

(ii) Draw a plot showing the variation of photoelectric current versus the intensity of incident radiation on a given photosensitive surface. 

24.

A 12.5 eV electron beam is used to bombard gaseous hydrogen at room temperature. Upto which energy levels the hydrogen atoms would be excited?

Calculate the wavelengths of the first member of Lyman and first member of Balmer series. 

25.

When Sunita, a class XII student, came to know that her parents are planning to rent out the top floor of their house to a mobile company she protested. She tried hard to convince her parents that this move would be a health hazard.

Ultimately her parents agreed:

(1) In what way can the setting up of transmission tower by a mobile company in a residential colony prove to be injurious to health?

(2) By objecting to this move of her parents, what value did Sunita display?
(3) Estimate the range of E.M waves which can be transmitted by an antenna of height 20 m. (Given radius of the earth = 6400 km)

26.

(a) Draw a labelled ray diagram showing the formation of a final image by a compound microscope at least distance of distinct vision.

(b) The total magnification produced by a compound microscope is 20. The magnification produced by the eye piece is 5. The microscope is focused on a certain object. The distance between the objective and eyepiece is observed to be 14 cm. If least distance of distinct vision is 20 cm, calculate the focal length of the objective and the eye piece. 

27.

a. A mobile phone lies along the principal axis of a concave mirror. Show, with the help of a suitable diagram, the formation of its image. Explain why magnification is not uniform.

b. Suppose the lower half of the concave mirror's reflecting surface is covered with an opaque material. What effect this will have on the image of the object? Explain.

28.

a) Deduce the expression, N = N₀ e^−λt, for the law of radioactive decay.

(b) (i) Write symbolically the process expressing the β⁺ decay of  . Also write the basic nuclear process underlying this decay.

(ii) Is the nucleus formed in the decay of the nucleus  , an isotope or isobar?

29.

(a) Describe a simple experiment (or activity) to show that the polarity of emf induced in a coil is always such that it tends to produce a current which opposes the change of magnetic flux that produces it.

(b) The current flowing through an inductor of self-inductance L is continuously increasing. Plot a graph showing the variation of

(i) Magnetic flux versus the current

(ii) Induced emf versus dI/dt

(iii) Magnetic potential energy stored versus the current. 

30.

(a) Draw a schematic sketch of an ac generator describing its basic elements. State briefly its working principle. Show a plot of variation of

(i) Magnetic flux and

(ii) Alternating emf versus time generated by a loop of wire rotating in a magnetic field.

(b) Why is choke coil needed in the use of fluorescent tubes with ac mains?