Definitions

Question 1

Define Luminous flux

Answer 1

The quantity of light energy coming from a source that is capable of producing a visual sensation and is measured in lumens.

Question 2

Define Illuminance

Answer 2

The measure of how much luminous flux is spread over a given area. This depends on the strength of the source, the distance from the source to the surface and the area covered. Illuminance is measured in Lux (lumens per square metre)

Question 3

Define Luminous intensity

Answer 3

The ability of a source to produce light in a given direction. It is the luminous flux emitted in a narrow cone containing the direction divided by the solid angle of the cone.

Question 4

Define Luminance

Answer 4

Also known as brightness. This is the intensity of light emitted in a direction for a certain area. Expressed as candelas per square metre.

Question 5

Define Luminous efficacy

Answer 5

This is the amount of light produced by a source for each watt of power consumed. It is used to compare the efficiency of one lamp to another and is measured in lumens per watt.

Question 6

Define the Inverse square law of illuminance

Answer 6

The illuminance at a point on a surface is inversely proportional to the square of the distance between the point and the source.

Question 7

Define the Cosine law of illuminance

Answer 7

If the normal to an illuminated surface is at an angle to the direction of the incident light, the illuminance is proportional to the cosine of the angle.

Question 8

What is the first law of refraction?

Answer 8

The incident ray and the refracted ray lie in the same plane which is normal to the refracting surface at the point of refraction.

Question 9

What is the second law of refraction?

Answer 9

The ratio of the sine of the incident angle is constant for any two media and for monochromic lens only.

Question 10

Define wavelength

Answer 10

Measured as the distance between two waves (crest to crest, trough to trough or midpoint to midpoint)

Question 11

Define velocity

Answer 11

The speed of a wave measured in metres per second

Question 12

Define frequency

Answer 12

The number of waves that travel through a point within a set time

Question 13

Define amplitude

Answer 13

The distance from the mid-point of a wave to its crest

Question 14

Define absolute refractive index

Answer 14

The ratio of the velocity of light in a vacuum and the velocity of light in a medium

Question 15

Define relative refractive index

Answer 15

The ratio of the velocity of light in two different media

Question 16

What is the wavelength of RED

Answer 16

760-622nm

Question 17

What is the wavelength of YELLOW

Answer 17

597–577nm

Question 18

What is the wavelength of GREEN

Answer 18

577–492nm

Question 19

What is the wavelength of BLUE

Answer 19

492–455nm

Question 20

Define Hue

Answer 20

This is the “statement” of the colour i.e. blue; red; green

Question 21

Define Saturation

Answer 21

This is the “depth” of colour

Question 22

Define Protanopia

Answer 22

Inability to distinguish the colour RED properly

Question 23

Define Deuteranopia

Answer 23

Inability to distinguish the colour GREEN properly

Question 24

Define Tritanopia

Answer 24

Inability to distinguish the colour BLUE properly

Question 25

What is the first law of reflection?

Answer 25

The incident ray, the reflected ray and the normal all lie in the same plane

Question 26

What is the second law of reflection?

Answer 26

The angle of incidence equals the angle of reflection

Question 27

Define total internal reflection

Answer 27

When the angle of incidence is greater than critical angle

Question 28

Define minimum deviation

Answer 28

The incident angles and the emergent angles are equal

Question 29

Define critical angle

Answer 29

The angle of reflection at the second surface is 90° to the normal, the angle of incidence at the second surface is the critical angle

Question 30

Define total internal reflection

Answer 30

The angle of incidence at the second surface is less than the critical angle