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ISC Class 12 Physics Solved Question Paper 2007

Short Answer Type

41. Calculate the equivalent energy in MeV of a unified atomic mass unit.

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42. What is meant by analogue and digital signal ? What is the symbol for a XOR gate ?

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43. Draw a labelled circuit diagram of a simple oscillator (using PNP or NPN transistor in common emitter configuration). On what factors does the frequency of the oscillator depend ?

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44. Draw energy band diagrams of conductors. semiconductors and insulators.

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Long Answer Type

45. In J.J. Thomson’s experiment for the determination of the ratio of the charge to the mass (e/m) for an electron, derive the formula in terms of E, B and V where E is the electric field intensity, B is the magnetic field intensity and V is the accelerating potential between anode and cathode.

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46.

For Bohr’s model of the hydrogen atom, the energy of electron in its ground state is found to be-13.6 eV.

(i) Draw an energy level diagram for the hydrogen atom and mark the values of energy (in eV) at n = 2 and n = ∝.

(ii) Obtain the maximum energy of a photon emitted by the hydrogen atom in eV.

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47.
(i) On what does the minimum wavelength of the continuous x-ray spectrum depend

(ii) When the filament current is increased, the intensity of the x-ray produced increases. Why?

(iii) Why is the structure of crystals studied by x-rays ?

(i)

The minimum wavelength of the continuous x-ray spectrum depends upon the voltage applied between the filament and the target of the x-ray tube.

Let V be the accelerating potential then,

$space space space space 1 half m v squared space equals space h nu subscript m a x end subscript rightwards double arrow space space h nu subscript m a x end subscript italic space italic equals italic space e V italic rightwards double arrow italic space fraction numerator h c over denominator lambda subscript m i n end subscript end fraction italic space italic equals italic space e V italic rightwards double arrow italic space lambda subscript m i n end subscript italic space italic equals italic space fraction numerator h c over denominator e V end fraction italic rightwards double arrow lambda subscript m i n end subscript italic space italic proportional to italic space italic 1 over V$

ii)

The intensity of x-rays depends on the number of electrons striking the target. The number of electrons emitted by the filament depends upon its temperature which increases with increase in filament current. Thus, the number of electrons hitting the target increases with increase in filament current, which in turn increases the intensity of x-ray produced.

(iii)

The distance between the atoms of crystals is of the order of wavelength of x-rays. When x-rays fall on crystal, they are diffracted. The diffraction pattern is helpful in the study of crystal structure.

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