JEE Physics - Optics

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Question - 1

Two lamps of liminous intensity of 8 Cd and 32 Cd respectively are lying at a distance of 1.2 m from each other. Where should a screen be placed between two lamps such that its two faces are equally illuminated due to two sources?

  • A 10 cm from 8 Cd lamp
  • B 10 cm from the 32 Cd lamp
  • C 40 cm from 8 Cd lamp
  • D 40 cm from 32 Cd lamp

Question - 2

A lamp is hanging at a height of 40 cm from the center of a table. If its height is increased by 10 cm the illuminance on the table will decrease by

  • A 10%
  • B 20%
  • C 27%
  • D 36%

Question - 3

A small lamp is hung at a height of 8 m above the center of a round table of diameter 16 m. The ratio of intensities of illumination of the center and at points on the circumference of the table will be

  • A 1:1
  • B 2:1
  • C \(2\sqrt { 2 } :1\)
  • D 3:2

Question - 4

A standard 48 Cd lamp placed 36 cm from the screen of a photometer produces the same illumination there as a lamp of unknown intensity located 45 cm away. What is the luminous intensitty of the latter lamp?

  • A 60 Cd
  • B 75 Cd
  • C 80 Cd
  • D 100 Cd

Question - 5

Light was falling on a surface at an angle of 450. The surface is lifted so that light now falls at an angle of 600. How is the illuminance affected?

  • A no effect
  • B \(2\sqrt { 2 } \) times
  • C \(\sqrt { 2 } \) times
  • D \(\frac { 1 }{ \sqrt { 2 } } \) times

Question - 6

If the distance between a point source and screen is made one-third, then intensity of light (I) and the initial intensity of light will be related as

  • A \(\frac { { I }_{ 0 } }{ 3 } \)
  • B \(I=\frac { { I }_{ 0 } }{ 3 } \)
  • C \(I= { { I }_{ 0 } }{ } \)
  • D \(I= { 9{ I }_{ 0 } }{ } \)

Question - 7

If luminous- efficiency of alamp is 2 lumen per watt and its luminous intensity is 42 candela, then, power of the lamp is

  • A 62 W
  • B 76 W
  • C 138 W
  • D 264 W

Question - 8

If the luminous intensity of a unidirectional bulb is 100 candela, then total luminous flux emitted from the bulb is

  • A 861 lumen
  • B 986 lumen
  • C 1256 lumen
  • D 1561 lumen

Question - 9

Time of exposure for a photographic print is 10 second, when a lamp of 50 Cd is placed at 1m from it. Then another lamp of luminous intensity I is used, and is kept at 2m from it. If the time of exposure now is 20 s, the value of I (in Cd) is

  • A 100
  • B 25
  • C 200
  • D 20

Question - 10

When light wave suffers reflection at the interface between air and glass, the change of phase in the reflected wave is equal to

  • A zero
  • B \(\lambda \)/2
  • C \(\lambda \)
  • D 2\(\lambda \)
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