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ISC Class 12 Physics Solved Question Paper 2009

Short Answer Type

41.

A sinusoidal voltage e = e₀ Sin (wt) is fed to a common emitter amplifier. Draw neatly labelled diagrams to show:

(i) Signal voltage

(ii) Output voltage of the amplifier.

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42. Make a truth table showing inputs at A and B and outputs at X, Y and Z for the combination of gates shown in figure below:

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Long Answer Type

43. With the help of a labelled diagram, obtain an expression for the electric field intensity ‘E’ at a point P in broad side position (i.e., equatorial plane) of an electric dipole.

Electric field intensity at a point on the broad side-on position equatorial line: Consider an electric dipole consisting of two equal but opposite charges -q and +q separated by a vector distance 2l. Let P be a point at a distance r from the centre of the dipole O. The electric intensity at P due to the dipole is the vector sum of the field due to the charge -q at A and +q at B.

Electric intensity at P due to - q = E_A =

But AP² = r² +l²;

where AO = OB = l

Magnitude of E_A is |E_A| =

The resultant intensity is the vector sum of

.

E_A and E_B can be resolved into two components.

The y-components of the fields cancel each other because E_A sin θ = E_B sin θ and they are oppositely directed. The x-components add up to give the resultant field E.

From the above two equations for E_eq and E_axial we find that the electric intensity at an axial point is twice the electric intensity at a point on the equatorial position, lying at the same distance from the centre of the dipole.

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44. What is meant by ‘Chromatic aberration’? A thin convex lens of focal length 30 cm and made of flint glass (dispersive power = 0.03) is kept in contact with a thin concave lens of focal length 20 cm and made of crown glass. Calculate the dispersive power of crown glass if the above said combination acts as an achromatic doublet.

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