Illumination

Which of the following information below is true for the light ray from a light source?

I. Light travels in a straight line

II. The speed of light is 300.000 km/s

III. The speed of light depends on the source

• Only I

• Only II

• Only III

• I and II

• I,II and II

The illumination at point O on the screen is E. In which direction does the light source should be moved to increase the illumination at point O ?

• Only 1

• Only 2

• Only 3

• 2 and 4

• 2,3 and 4

Illumination at point O from both light sources is the same. What is the ratio of the luminous intensity of the light sources  $\frac{I_1}{I_2}$   ?

• $\frac{1}{2}$

• 1

• $\frac{1}{4}$

• 2

• 4

The illumination of a light source that has luminous intensity I at a distance d is E.
If different light source with lumious intensity 3I is used, find the illumination at 3d distance ?

•  $\frac{1}{4}E$  

•  $\frac{1}{3}E$  

•  $\frac{1}{2}E$  

• 1

• 3

Which of the following statement(s) is true ?

I. The unit of luminous flux is lumen.

II. The unit of luminous intensity is candela.

III. The unit of illumination is lux.

• Only I

• Only II

• Only III

• I and II

• I,II and III

The decreasing order of illuminations at point K, L and M are EM > EK > EL Which one is correct for the distances d1, d2, d3 from the light source ?                                 

• d1 > d2 > d3  

•   d3 > d2 > d1 

•  d3 >d1 > d2         

•  d1 > d3 > d2 

• d2 > d1 > d3