Light waves (chapter 12)

Question 1

What are luminous objects?

Answer 1

Objects which emit their own light.

Question 2

How do we see non-luminous objects?

Answer 2

We see non-luminous objects because of the light they reflect.

Question 3

What happened when a ray of light strike a mirror?

Answer 3

angle of incidence = angle of reflection

Question 4

What is refraction?

Answer 4

When a ray of light travel across the border between two different medium, the change in speed cause the ray to change direction.

Question 5

What is the speed of light in glass?

Answer 5

200 million m/s

Question 6

What happens if the ray strikes the boundary between the two media at 90 degrees?

Answer 6

The ray continues without a change of direction.

Question 7

How is the amount of refraction described?

Answer 7

Refraction index

Question 8

Refraction occurs at —– medium.

Answer 8

2

Question 9

State the formula to find refractive index?

Answer 9

n = sin i / sin r

Question 10

Which object is needed for reflection of rays?

Answer 10

Mirror

Question 11

What are transparent objects?

Answer 11

• Water
• Ice
• Glass
• Diamond

Question 12

Which surface does regular reflection and diffused reflection occur?

Answer 12

Regular reflection - smooth surface
Diffused reflection - rough surface

Question 13

Which kind of waves doesn’t need medium?

Answer 13

EM waves

Question 14

What is refractive index?

Answer 14

Amount that use to describe how much do different materials can bend rays of light.

Question 15

What is total internal reflection?

Answer 15

Total internal reflection occurs when rays of light are travelling towards a boundary with a less optically dense medium.

Question 16

What is critical angle?

Answer 16

The critical angle is the smallest possible angle of incidence at which light rays are totally internally reflected.

Question 17

What happen when Angle of incidence (i) is greater than the critical angle?

Answer 17

All the light is internally reflected at the boundary and no light is refracted.

Question 18

What are conditions needed for total internal reflection?

Answer 18

• (i) > (c)
• Light must travel from more dense to less dense medium

Question 19

What are the equipment to investigate total internal reflection?

Answer 19

• Semi-circular glass box
• A ray box

Question 20

What is the formula to find critical angle?

Answer 20

sin c = 1/ n (refractive index)

Question 21

How much is the critical angle for light passing from glass to air.

Answer 21

42 degree

Question 22

Why is it better to use prisms in a periscope?

Answer 22

The images produced by prisms are often brighter and clearer than those produced by mirrors.

Question 23

What are the uses of total internal reflection?

Answer 23

• Prismatic periscope
• Bicycle and car reflectors
• Binoculars
• Optical fibers
• Endoscope
• Telecommunications

Question 24

How is optical fiber composed of?

Answer 24

It is composed of 2 different type of glass which the center has high refraction index glass surrounded by glass with low refraction index.

Question 25

What does each side of a pair of binoculars contain?

Answer 25

Two prisms to totally internally reflect the incoming light.

Question 26

How will the binocular without the prisms be like?

Answer 26

Without the prisms, the binoculars would have to be very long to obtain large magnifications.

Question 27

How is it make sure that light entering the inner core in optical fiber is always internally reflected?

Answer 27

As the fibers are narrow, light entering the inner core always strike the boundary of the two glasses at an angle that is greater than critical angle.

Question 28

What is the benefit of the use of endoscope?

Answer 28

- less stressful for patients - usually leads to a more rapid recovery.

Question 29

Why modern telecommunications systems use optical fibers rather than copper wires?

Answer 29

Less energy is lost by using optical fibers.

Question 30

How are electrical signals from telephone are converted?

Answer 30

They are converted into light energy produced by tiny lasers.

Question 31

What changes the pulses of light back in electrical signals in optical fiber?

Answer 31

Light-sensitive detector at the other end.

Question 32

How much is the critical angle for light passing from water to air?

Answer 32

49 degree

Question 33

What is the relationship between refractive index (n) and critical angle (c).

Answer 33

Inversely proportional

Question 34

What is the relationship between density and refractive index (n).

Answer 34

Directly proportional