### Physics - Optics

#### 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$\lambda$