51.

Given below is the circuit diagram of an AM demodulator. For good demodulation of AM signal of carrier frequency f, the value of RC should be

 

• RC = 1/f

• RC < 1/f

• RC ≥ 1/f

• RC >> 1/f

Assertion:  Electromagnetic waves with frequencies smaller than the critical frequency of ionosphere are used for communication using sky wave propagation. 

Reason:  The refractive index of the ionosphere becomes very high for frequencies higher than the critical frequency.

• If both assertion and reason are true and reason is the correct explanation of the assertion

• If both assertion and reason are true but reason is not the correct explanation ofthe assertion

• If assertion is true, but reason is false

• Both assertion and reason are false statements

Assertion:  The binding energy per nucleon, for nuclei with atomic mass number A > 100 decreases with A. 

Reason:  The nuclear forces are weak for heavier nuclei.

• If both assertion and reason are true and reason is the correct explanation of the assertion

• If both assertion and reason are true but reason is not the correct explanation of the assertion

• If assertion is true, but reason is false

• Both assertion and reason are false statements

Assertion: In common base configuration, the current gain of the transistor is less than unity. 

Reason: The collector terminal is reverse biased for amplification.

• If both assertion and reason are true and reason is the correct explanation of the assertion

• If both assertion and reason are true but reason is not the correct explanation of the assertion

• If assertion is true, but reason is false

• Both assertion and reason are false statements

Assertion:  Standard optical diffraction gratings cannot be used for discriminating between different X-ray wavelengths. 

Reason: The grating spacing is not of the order of X-ray wavelengths.

• If both assertion and reason are true and reason is the correct explanation of the assertion

• If both assertion and reason are true but reason is not the correct explanation of the assertion

• If assertion is true, but reason is false

• Both assertion and reason are false statements

Assertion: The photoelectrons produced by a monochromatic light beam incident on a metal
surface, have a spread in their kinetic energies. 

Reason: The work function of the metal varies as a function of depth from the surface.

• If both assertion and reason are true and reason is the correct explanation of the assertion

• If both assertion and reason are true but reason is not the correct explanation of the assertion

• If assertion is true, but reason is false

• Both assertion and reason are false statements

Assertion:  A p-n junction with reverse bias can be used as a photo-diode to measure light intensity. 

Reason:  In a reverse bias condition the current is small but is more sensitive to changes in incident  light intensity.

• If both assertion and reason are true and reason is the correct explanation of the assertion

• If both assertion and reason are true but reason is not the correct explanation ofthe assertion

• If assertion is true, but reason is false

• Both assertion and reason are false statements

Assertion:  Cobalt-60 is useful in cancer therapy. 

Reason:  Cobalt-60 is a source of y-radiations capable of killing cancerous cells.

• If both assertion and reason are true and reason is the correct explanation of the assertion

• If both assertion and reason are true but reason is not the correct explanation of the assertion

• If assertion is true, but reason is false

• Both assertion and reason are false statements

Assertion:  In optical fibre, the diameter of the core is kept small. 

Reason:  This smaller diameter of the core ensures that the fibre should have incident angle more than the critical angle required for total internal reflection.

• If both assertion and reason are true and reason is the correct explanation of the assertion

• If both assertion and reason are true but reason is not the correct explanation of the assertion

• If assertion is true, but reason is false

• Both assertion and reason are false statements

A leaf which contains only green pigments is illuminated by a  laser light of wavelength  0.6328 μm. It would appear to be

• brown

• black

• red

• green