Chapter 13~waves 🌊

Question 1

What are waves?

Answer 1

Waves are a means of transferring energy ⛮ or “information” from one point to another caused by vibrations. Also referred to as a periodic disturbance travelling through space, characterised by a vibrating medium.

Question 2

Definition of progressive waves

Answer 2

A wave that carries energy ⛮ from one place/posifion to another through a material or vacuum.

Question 3

Definition of a mechanical wave : and an example

Answer 3

°it is a wave that requires a material medium to move through, for example sound 🔊.

Question 4

Definition of displacement :

Answer 4

The distance of a point on the wave 🌊 from its underdisturbed position or equilibrium position

Question 5

Definition of amplitude, A:

Answer 5

The maximum displacement of any point on the wave from its underdisturbed position / equilibrium

Question 6

A greater amplitude result in what for sound waves?

Answer 6

A louder sound 🔊

Question 7

Definition of wavelength :

Answer 7

The distance from any point on a wave to the next exactly similar point, measured in metres. (e.g. From crest to crest)

Question 8

Definition of period, T:

Answer 8

The time take for one complete oscillation of a point in a wave, measured in seconds.

The time taken for one wave /oscillation to pass a point.

The time taken for a particle to complete a full oscillation.

Question 9

Definition of frequency, f :

Answer 9

The number of oscillation per unit time of a point in a wave, measured in hertz (Hz).

The number of waves/oscillations that pass a point per second.

Question 10

A higher pitch is a result of..

Answer 10

A higher frequency

Question 11

Definition of a longitudinal wave : and an example

Answer 11

Waves in which the particles of the medium vibrate parallel to the direction of the wave propagation (motion) or the wave velocity.

Example: sound 🔊

Question 12

Definition of transverse waves :

Plus an example

Answer 12

Waves in which the particles of the medium vibrate at right angles or perpendicular to the wave motion /propagation /velocity.

Example : light wave

Question 13

Frequency is the reciprocal of?

Answer 13

The period (T)

F= 1/T

Question 14

Definition of compressions 🗜 :

Answer 14

A region in a longitudinal wave where the particles are closest together and where the air pressure is greater than its mean value.

Question 15

Definition of rarefaction :

Answer 15

A region in a longitudinal wave where the particles are furthest apart and the air pressure is less than its mean value.

Question 16

Definition of phase difference:

Answer 16

°the difference in the phases of 2 oscillating particles, experienced in degrees or radians. It also refers to the amount by which one wave leads or lags another wave.

Question 17

How many degrees is equivalent 1 radian?

Answer 17

180°

Question 18

Intensity of a wave 🌊 :

Answer 18

The rate of energy ⛮ transmitted per unit area at right angles to the wave velocity.

Question 19

What are the units for intensity?

Answer 19

Watts per square metre, Wm-2

Question 20

Formula for intensity

Answer 20

Intensity = power /cross-sectional area

Question 21

The intensity of a wave generally decreases as it travels along for 2 reasons :

Answer 21

1. The wave may ‘spread out’

2. The wave may be absorbed or scattered

Question 22

Intensity is proportional to..

Answer 22

The square of the amplitude.

Question 23

What is the wave equation and how is it derived in two steps?

Answer 23

v = f × ♈

v-velocity
F-frequency
♈-wavelength

Derived from :
Step 1 :
speed =distance / time

v= ♈÷ 1/T

Step 2 : rewrite this

v = ♈ x f

Bec 1/T =f

Question 24

What is the Doppler effect?

Answer 24

The change in frequency or wavelength of a wave 🌊 observed when the source of the wave is moving towards or away from the observer (or the observer is moving relative to the source

Question 25

Short meaning of the Doppler effect

Answer 25

It is the change in frequency due to the relative motion between the observer and source.

Question 26

Formula for observed frequency =

Answer 26

f(o) =[f(s) v] /[v +/- v(s)]

Question 27

When do you use a plus ➕ in the observed frequency formula?

Answer 27

This is used when either the observer / source is moving AWAY from the other

Question 28

When do you use a minus ➖ in the observed frequency formula?

Answer 28

When there is movement towards of either the observer or source

Question 29

What two things are unaffected by the movement of the source?

Answer 29

1. The frequency f(s) of the source, it still emits f(s) waves per second 2. The speed v of the waves

Question 30

Definition of electromagnetic spectrum :

Answer 30

The family of transverse 🚦 waves 🌊 that travel through a vacuum at a speed of 3.00 × 10^8. They are a group of waves with common properties

Question 31

The five properties of electromagnetic waves 🌊 :

Answer 31

1. All travel at the speed 🚤 of light 🚦 c= 3 × 10^8 Therefore (c =f ♈) 2. All can be polarised 3. All can be reflected, refracted, diffracted and absorbed 4. All travel through a vacuum 5. All can undergo interference

Question 32

What are the seven electromagnetic waves? 🌊 In order of decreasing wavelength

Answer 32

1. Radio waves 2. Microwaves 3. Infared 4. visible 5. Ultra-violet 6. X-rays 7. Gamma rays (y-rays)

Question 33

What is the wavelength range in metres of radio 📻 waves?

Answer 33

> 10^6 to 10^-1

Question 34

What is the wavelength range in metres of microwaves?

Answer 34

10^-1 to 10^-3

Question 35

What is the wavelength range in metres of infared?♥

Answer 35

10^-3 to 7×10^-7

Question 36

What is the wavelength range in metres of visible waves?

Answer 36

7×10 ^-7(red) to 4× 10^-7 (violet)

Question 37

What is the wavelength range in metres of ultraviolet waves?

Answer 37

4 × 10^-7 to 10^-8

Question 38

What is the wavelength range in metres of x-rays? ☠️💀

Answer 38

10^-8 to 10^-13

Question 39

What is the wavelength range in metres of x-rays? ☠️💀

Answer 39

10^-8 to 10^-13

Question 40

What is the wavelength range in metres of Y-rays ( gamma rays)?

Answer 40

10^-10 to 10^-16

Question 41

State all 7 ranges of wavelengths from decreasing wavelengths :

Answer 41

R : >10^6 to 10^-1 M: 10^-1 to 10 ^-3 I: 10^-3 to 7 × 10^-7 V: 7 × 10^-7 (red) to 4 ×10 ^-7 (violet) U: 4× 10 ^-7 to 10 ^-8 X : 10 ^-8 to 10^-13 Y: 10^-10 to 10 ^-16

Question 42

Definition of an electromagnetic wave :

Answer 42

A disturbance in the electric and magnetic fields in space

Question 43

What is polarisation?

Answer 43

It is the process in which transverse waves are restricted to vibrate in one plane (only)