🪞 Optics (DNF)

Question 1

define light

Answer 1

It is a form of energy that travels away from the source producting it

Question 2

what is the speed of light?

Answer 2

3 x 10^8 m s-1

Question 3

define a self-luminous object

Answer 3

an object that gives out its own light

eg. the sun, stars, fire

Question 4

define a non-luminous object

Answer 4

an object which doesn’t give out it’s own light
*You can only see it when light from another source bounces off this object and goes into your eye

Question 5

how do we know that light is a form of energy?

Answer 5

• electrical energy => light energy
• Light can cayse a photocell to produce electric current (Solar panels)

Question 6

How does light travel? Straight? Diagonally? etc?

Answer 6

Light usually travels in straight lines.

Question 7

What kinds of beams of light are there (name the three)?

Answer 7

1. Parallel beam (straight forward)
2. Converging beam (moving from out to in (narrorer))
3. Diverging beam (moving from in to out (spreading out))

Question 8

Demonstration to show that light travels in a straight line

what is the equipment needed for this demonstration?

Answer 8

bulb, 3-4 sheets of carboard (small hole in the centre each), a piece of thread

Question 9

Demonstration to show that light travels in a straight line

Outline the setup of this demonstration

Answer 9

• Arrange the bulb and the cardboard sheets with holes such that they form a line.
• Pass a piece of thread through the holes, ensuring they are aligned.

Question 10

Demonstration to show that light travels in a straight line

Outline the actual demonstration (what to do)

Answer 10

• Attempt to see the bulb through the holes.
• Observation: The bulb is visible only when the holes are aligned in a straight line.

Question 11

Demonstration to show that light travels in straight lines

what is the conclusion of this demo?

Answer 11

• Light cannot turn corners to pass through the holes if they are not in line.
• This demonstrates that light travels in straight lines.

Question 12

define the reflection of light

Answer 12

It is the bouncing of light off an object which is then called a reflection

Question 13

define a light ray

Answer 13

the direction light is travelling

Question 14

define diffuse reflection

Answer 14

reflected light that is scattered in all directions from the object (this is how we see things => then everyone can see this object)

eg. a table

Question 15

define a regular reflection

Answer 15

• the light that shines off a smooth/polished object (eg. mirror)
• Light falling on it is not scattered in all directions => instead its reflected off (copies the object in a way)

Question 16

What are the laws of reflection of light?

Answer 16

1. The incident ray, the normal at the point of incidence and the reflected ray all lie in the same plane.
2. The angle of incidence is equal to the angle of reflection (i = r).

Question 17

what is it called if a mirror is flat?

Answer 17

a plane mirror

Question 18

regular reflection diagram

explain the normal at the point of incidence

Answer 18

the line drawn (90 degrees) perpendicular to the mirror *where the ray strikes the mirror

Question 19

regular reflection diagram

explain the reflected ray

Answer 19

the ray of light leaving the mirror

Question 20

regular reflection diagram

explain the angle of incidence

Answer 20

the angle between the incident ray and the normal (symbol is ‘i’)

Question 21

regular reflection diagram

explain the angle of reflection

Answer 21

the angle between the reflected ray and the normal (symbol is ‘r’)