Physics | CBSE Board | Grade 12 | 2012

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(b) Identify the equivalent gate for the following circuit and write its truth table.

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How will the (i) energy stored and (ii) the electric field inside the capacitor be affected when it is completely filled with a dielectric material of dielectric constant ′K′?

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(i) constructive interference and

(ii) destructive interference at a point on the screen.

(b) A bream of light consisting of two wavelengths, 800nm and 600nm is used to obtain the interference fringes in a Young's double slit experiment on a screen placed 1.4m away. If the two slits are separated by 0.28nm, calculate the least distance from the central bright maximum where the bright fringes of the two wavelengths coincide.

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Using Einstein's photoelectric equations show how the cut-off voltage and threshold frequency for a given photosensitive material can be determined with the help of a suitable plot/graph.

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(i) The resistance of the bulb;

(ii) The rms current through the bulb.

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(i) Complete the ray diagram showing the image formation of the object.

(ii) How will the position and intensity of the image be affected if the lower half of the mirror's reflecting surface is painted black?

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(b) A rectangular loop of size l×b carrying a steady current I is placed in a uniform magnetic field →B. Prove that the torque →τ acting on the loop is given by →τ=→m×→B where →m is the magnetic moment of the loop.

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(i) Show that the net force acting on it is zero.

(ii) The dipole is aligned parallel to the field. Find the work in rotating it through the angle of 180∘.

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