IIT JEE Main / Advanced Physics 2018 : Geometrical Optics – kind of questions to expect /practice tests.

A . Objective questions with only one correct answer  –

1  . Rays of light from the sun falls on a biconvex lens of focal length f and the circular image of the Sun of radius r is formed on the focal plane of the lens . Then ,

  • (a)  area of image is π r² and area is directly proportional of  f  .
  • (b)  area of image is π r² and area is directly proportional to r².
  • (c)  intensity of image increases if  f is increased.
  • (d)  if lower half of the lens is covered with black paper , area will become half .

2  . A ray of light travelling in water is incident on its surface open to air . The angle of incidence is θ , which is less than the critical angle . Then , there will be –

  • (a)  only a reflected ray and no refracted ray .
  • (b)  only a refracted ray and no reflected ray .
  • (c)  a reflected ray and a refracted ray and the angle between them would be less than 180° – 2 θ .
  • (d)  a reflected ray and a refracted ray and the angle between them would be greater than 180° – 2 θ .

3  . A convex lens is in contact with a concave lens . The magnitude of the ratio of their focal lengths is 2/3 . Their equivalent focal length is 3o cm . What are their individual focal lengths ?

  • (a)  – 15 , 10
  • (b)  – 10 , 15
  • (c)  75 , 50
  • (d)  – 75 , 50

4  . A container is filled with water ( μ = 1.33 ) upto a height of 33.25 cm . A convex mirror is placed 15 cm above the water level and the image of an object is placed at the bottom is formed 25 cm below the water level . Focal length of the mirror is –

  • (a)  15 cm
  • (b)  20 cm
  • (c)  – 18.31 cm
  • (d)  10 cm

5  . A short linear object of length b lies along the axis of a concave mirror of focal length f at a distance u from the pole of the mirror . The size of the image is approximately equal to

  • (a)  b ( u – f / f )½
  • (b)  b ( b / b – f )½
  • (c)  b ( u – f / f )
  • (d)  b ( f / u – f ) ²

6  . A thin prism P1 with angle 4° and made from glass of refractive index 1.54 is combined with another thin prism P2 made from glass of refractive index 1.72 to produce dispersion without deviation . The angle of the prism P2 is –

  • (a)  5.33°
  • (b)  4°
  • (c)  3°
  • (d)  2.6°

7  . A ray enters a glass slab at an angle α from air where the refractive index varies along the slab as μ = μ0– k r² , where r is the distance measured along the normal and μ0 , k are positive constants . If the glass slab is sufficiently thick , how far along the normal will the ray go before it is reflected back ?

  • (a)  μ0 – sin θ / k
  • (b)  μ0 + sin θ / k
  • (c)  √ ( μ0 – sin θ / k )
  • (d) √ ( μ0+ sin θ / k )

8 . A bird is flying up at an angle sin-1 ( 3/5 ) with the horizontal. A fish in a pond looks at the bird when the bird is vertically above it . The angle at which the bird appears to fly , to the fish is  –   ( nwater= 4/3 )

  • (a)  sin-1 ( 3/5 )
  • (b)  sin-1 ( 4/5 )
  • (c)  45°
  • (d)  sin-1 ( 9/16 )

9  . A glass sphere of radius 5.0 cm and refractive index 1.6 is used to construct a paperweight by slicing through the sphere on a plane that is 2.0 cm from the centre of the sphere . Moreover , this plane is perpendicular to a radius of the sphere that passes through the centre of the circle formed by the intersection of the plane and the sphere . The paperweight is placed on a table and viewed from directly above by an observer who is 8.0 cm from the tabletop. When viewed through the paperweight , how far away does the table top appear to the observer ?

  • (a)  7.42 cm
  • (b)  6.5 cm
  • (c)  3 cm
  • (d)  4.44 cm

10 . A fish rises up vertically in a pond with a speed of 4 cm/s and notices a bird which is diving downwards towards the fish. The speed of the bird appears to be 16 cm/s , to the fish . If the refractive index of the water is 4/3 , the actual velocity of the bird is –

  • (a)  4 cm/s
  • (b)  9 cm/s
  • (c)  16 cm/s
  • (d)  6.2 cm/s

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