51.

Light  is  incident  normally  on  a  diffraction  grating  through  which  the  first  diffraction  is seen  at 32°. In  this  case  the  second  order  diffraction will  be

• at 80^o

• at 64^o

• at 48^o

• there is no second order diffraction

An object 5 cm tall is placed 1 m from a concave spherical mirror which has a radius of curvature of 20 cm. The size of the image is

• 0.11 cm

• 0.50 cm

• 0.55 cm

• 0.60 cm

The magnifying power of a compound microscope increase with

• the focal length of objective lens is increased and that of eye lens is decreased

• the focal length of eye lens is increased and that of objective lens is decreased

• focal lengths of both objects and eye-piece are increased

• focal lengths of both object and eye-piece

A thread is tied slightly loose to a wire frame as in figure and the frame is dropped into a soap solution and taken out. The frame is completely covered with the film. When the portion A is punctured with a pin, the thread

• become concave towards A

• become convex toward A

• either (a)  or  (b) depending on the size of A with respect to B

• remains in the initial position

Assertion: The colour of the green flower seen through red glass appears to be dark

Reason: Red glass transmits only red 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:  It is essential that all the lines available in the emission spectrum will also be available in the absorption spectrum.

Reason: The spectrum of hydrogen atom is only absorption spectrum.

• 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:  A double convex lens ( μ = 1.5 ) has focal length 10 cm. When the lens is immersed in water ( μ = 4/3 ) its focal length becomes 77 cm.

Reason:  $\frac{1}{\mathrm{f}} = \frac{{\mathrm{\mu }}_{\mathrm{g}} - {\mathrm{\mu }}_{\mathrm{w}}}{{\mathrm{\mu }}_{\mathrm{w}}}$$\left(\frac{1}{{\mathrm{R}}_1} - \frac{1}{{\mathrm{R}}_2}\right)$

• 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: Diode lasers are used as optical sources in optical communication.

Reason:  Diode lasers consume less energy.

• 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: Stopping potential depends upon the frequency of incident light but is independent of the intensity of the light. 

Reason:  The maximum kinetic energy of the photoelectrons is proportional to stopping potential.

• 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:  ⁹⁰Sr from the radioactive fall out from a nuclear bomb ends up in the bones of human beings through the milk consumed by them. It causes impairment of production of red blood cells.

Reason: The energies β-particles emitted in the decay of  ⁹⁰Sr damage the bone marrow.

• 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