51.

The circuit as shown in figure,

the equivalent gate is

• NOR gate

• OR gate

• AND gate

• NAND gate

Ratio of longest wavelengths corresponding to Lyman and Balmer series in hydrogen spectrum is

• $\frac{7}{29}$

• $\frac{9}{31}$

• $\frac{5}{27}$

• $\frac{3}{23}$

Assertion: In a communication system based on amplitude modulation the modulation index is kept <1. 

Reason: It ensures minimum distortion of signal.

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

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

• If assertion is true but reason is false.

• If both assertion and reason are false.

Assertion:  If optical density of a substance is more than that of water then the mass density of substance can be less than water. 

Reason:  Optical density and mass density are not related.

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

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

• If assertion is true but reason is false.

• If both assertion and reason are false.

Assertion:  ${}_{27}{}^{60}\mathrm{Co}$  is a source of gamma radiation.

Reason: Gamma emission is due to nuclear decay.

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

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

• If assertion is true but reason is false.

• If both assertion and reason are false.

Assertion: When light ray is incident at polarising angle on glass, refracted light is partially polarised. 

Reason:  The intensity of light decreases in polarisation.

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

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

• If assertion is true but reason is false.

• If both assertion and reason are false.

Assertion: A laser beam of 0.2 W power can drill holes through a metal sheet, whereas a 1000 W torch-light cannot. 

Reason: The frequency of laser light is much higher than that of torch light.

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

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

• If assertion is true but reason is false.

• If both assertion and reason are false.

Assertion:  Electric appliances with metallic body. e.g., heaters, presses etc., have three pin connections, whereas an electric bulb has a two pin connection. 

Reason: Three pin connections reduce heating of connecting cables.

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

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

• If assertion is true but reason is false.

• If both assertion and reason are false.

Assertion: The sun rises some time before the actual sun-rise.

Reason:  Because of the refraction through the different layers of atmosphere.

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

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

• If assertion is true but reason is false.

• If both assertion and reason are false.

Assertion: Resolving power of a telescope depends only on wavelength.

Reason:  This is proportional to square of wavelength.

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

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

• If assertion is true but reason is false.

• If both assertion and reason are false.