Physics

CBSE Class 12

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State the law of radioactive decay.

Plot a graph showing the number (N) of undecayed nuclei as a function of time (t) for a given radioactive sample having half-life T_{½.}

Law of radioactive decay states that, the number of nuclei undergoing decay per unit time, at any instant, is proportional to the total number of nuclei present in the sample at that instant.

Number of undecayed nuclei at t = 3T_{1/2} is

And, at t = 5T_{1/2 }the number of undecayed nuclei is

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32.

(i) With the help of a labelled diagram, describe briefly the underlying principle and working of a step up transformer.

(ii) Write any two sources of energy loss in a transformer.

(iii) A step up transformer converts a low input voltage into a high output voltage.

Does it violate law of conservation of energy? Explain.

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33.

Derive an expression for the impedance of a series LCR circuit connected to an AC supply of variable frequency.

Plot a graph showing variation of current with the frequency of the applied voltage.

Explain briefly how the phenomenon of resonance in the circuit can be used in the

Tuning mechanism of a radio or a TV set. 4688 Views

34.

(a) Draw a ray diagram to show refraction of a ray of monochromatic light passing through a glass prism.

Deduce the expression for the refractive index of glass in terms of angle of prism and angle of minimum deviation.

(b) Explain briefly how the phenomenon of total internal reflection is used in fiber optics.

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35.

(a) Obtain lens makers formula using the expression

Here the ray of light propagating from a rarer medium of refractive index (n_{1}) to a denser medium of refractive index (n_{2}) is incident on the convex side of spherical refracting surface of radius of curvature R.

(b) Draw a ray diagram to show the image formation by a concave mirror when the object is kept between its focus and the pole. Using this diagram, derive the magnification formula for the image formed.

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