Waves And Their Properties And Optics

Question 1

What are waves?

Answer 1

Waves are disturbances that transfer energy through space or a medium without transferring matter.

Question 2

What are some classifications of waves?

Answer 2

•Mechanical Waves:
Require a medium (e.g., water waves, sound waves).

•Electromagnetic Waves:
Can travel through a vacuum(space) (e.g., light, radio waves).

•Matter Waves:
Associated with the motion of particles (quantum mechanics).

Question 3

What are the 5 basic characteristics of waves?

Answer 3

Amplitude, wavelength, time, direction of propagation and time period

Question 4

What is wavelength?

Answer 4

A wavelength is defined as the minimum distance covered by the wave before it starts repeating itself. It is measured in meters and it’s symbol is λ

Question 5

What is Time period?

Answer 5

Time period of a sound wave is defined as the time required for one complete cycle.

The time period is measured in seconds.

• The time period is also used to find out the frequency of the wave, the reciprocal of the time period gives the frequency of the wave.

Question 6

What is one cycle of a wave?

Answer 6

One cycle of the wave is defined by one complete rarefaction(reduction) and compression in the vibration.

Question 7

What is the frequency/pitch of a wave?

Answer 7

•The frequency of the sound wave is defined as the number of cycles completed by the wave in 1 second.
•The frequency of the wave can also be defined as the number of vibrations created by the wave in one second.
•The SI unit of frequency is Hertz (Hz)
•An example of the frequency of the wave is

Question 8

Define the key properties of a wave.

Answer 8

•A. Amplitude (A)
•The maximum displacement of a point on a wave from its equilibrium position.
•Determines the wave’s intensity or loudness.
•B. Wavelength (λ)
•The distance between two consecutive points in phase.
•Measured from crest to crest or trough to trough. C. Frequency (f)
•The number of oscillations or cycles per unit time.
•Measured in hertz (Hz).
D. Period (T)
•The time it takes for one complete cycle of a wave.
•Inversely proportional to frequency (T=1/f1).
E. Velocity (v)
•The speed at which a point on the wave travels.
•Calculated as the product of frequency and wavelength (⋅v=f⋅λ).

Question 9

The velocity of a wave is 600m/sec and the wavelength is given as 40Hz. What will be the wavelength of this wave?

Answer 9

15m

Question 10

The Time period of a wave is 2 seconds and the wavelength is given as 20 meters. There is another wave with a time period of 6 seconds and a wavelength of 60 meters. Which of the two waves have more velocity.

Answer 10

10ms-1

Question 11

Two waves having Frequencies of 20Hz and 100Hz are given. Which wave has more Time period?

Answer 11

0.01s

Question 12

How does light travel?

Answer 12

• Light travels in straight-line paths called rays.
• Assumes a very narrow beam of light.

Question 13

What is the normal?

Answer 13

The normal is an imaginary line perpendicular to a boundary between two materials or a surface.

Question 14

what is the relationship between the angle of incidence and angle of reflection?

Answer 14

Angle of incidence is equal to angle of reflection

Question 15

What is refraction?

Answer 15

The change in direction that occurs when light passes at an angle across a boundary between two transparent substances

Question 16

How does light bend at the boundary between two substances?

Answer 16

At a boundary between two transparent substances, the light ray bends:
* towards the normal if it passes into a more dense substance
* away from the normal if it passes into a less dense substance

Question 17

What is the refractive index of glass?

Answer 17

The ratio of sin 𝑖/sin 𝑟 is referred to as the refractive index, n, of glass.

For a light ray travelling from air into a transparent substance, the refractive index of the substance, n =
sin 𝑖/sin r

Question 18

Why does refraction occur?

Answer 18

Refraction occurs because the speed of the light waves is different in each substance.
The amount of refraction that takes place depends on the speed of the waves in each
substance.

sin 𝑖/sin 𝑟
=𝐶/𝐶𝑠

𝐶 is the speed in vacuum and 𝐶𝑠
is the speed in the other substance
Therefore, the refractive index of the substance, 𝑛𝑠 = 𝐶/𝐶𝑠

This equation shows that the smaller the speed of light is in a substance, the greater is
the refractive index of the substance.

Question 19

What is interference?

Answer 19

Interference is a phenomenon in which two waves superpose ( interact) to form a resultant
wave of greater, lower, or the same amplitude.

Question 20

When does total internal refraction occur?

Answer 20

When a light ray travels from glass into air, it refracts away from the normal. lf the angle of incidence is increased to a certain value known as the critical angle, the light ray refracts along
the boundary.

If the angle of incidence is increased further, the light ray undergoes total internal reflection at the
boundary.

Sin 0c = n2/n1 x sin90 = n2/n1

Question 21

How can refraction be calculated at a boundary between two substances?

Answer 21

Consider a light ray crossing a boundary from a substance in which the speed of light is 𝐶1 to a substance in which the speed of light is 𝐶2. Using the same theory we have:
sin 𝑖/sin 𝑟 = 𝐶1/𝐶2

𝑟 = 𝑡ℎ𝑒 𝑎𝑛𝑔𝑙𝑒 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑡ℎ𝑒 𝑟𝑒𝑓𝑟𝑎𝑐𝑡𝑒𝑑 𝑟𝑎𝑦 𝑎𝑛𝑑 𝑡ℎ𝑒 𝑛𝑜𝑟𝑚𝑎𝑙.
𝑖 = 𝑡ℎ𝑒 𝑎𝑛𝑔𝑙𝑒 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑡ℎ𝑒 𝑖𝑛𝑐𝑖𝑑𝑒𝑛𝑡 𝑟𝑎𝑦 𝑎𝑛𝑑 𝑡ℎ𝑒 𝑛𝑜𝑟𝑚𝑎𝑙

n1sin01 = n2sin02

therefore sin 𝜃1/sin 𝜃2
= n

Question 22

How can refractive index be calculated?

Answer 22

𝑛 = 𝑡ℎ𝑒 𝑠𝑝𝑒𝑒𝑑 𝑜𝑓 𝑙𝑖𝑔ℎ𝑡 𝑖𝑛 𝑎 𝑣𝑎𝑐𝑢𝑢𝑚 /
the speed of light in the transparent substance

Question 23

What are the conditions for total internal reflection?

Answer 23

In general, total internal reflection can only take place if:
1) the incident substance has a larger refractive index than the other substance
2) the angle of incidence exceeds the critical angle.

Sin 0c = n2/n1 x sin90 = n2/n1