PHYSICS 4.1 WAVES

Question 1

What do waves do

Answer 1

Waves transfer energy and information

Question 2

What is a wave

Answer 2

A wave may be thought of as a spreading of disturbance from one place to another (e.g. light, heat, sound waves)

Question 3

A wave is an energy carrier

Question 4

The source of waves is vibration or oscillation

Question 5

There are two types of waves
1. Transverse
2. Longitudinal

Question 6

Transverse Waves -
Waves where the movement of particles are up and down, are called transverse waves
Transverse waves travel in a direction perpendicular to the direction of vibration (90 degree)

Question 7

Longitudinal -
Waves when the movement of particles are backwards and forwards we known as longitudinal

Question 8

Each longitudinal wave is a compression followed by a rare faction

Question 9

Longitudinal waves travel in a direction parallel to the direction of vibration (e.g. sound waves)

Question 10

Crest and Trough -
These are the highest and lowest points of a wave. The highest points/peaks are called crest and the lowest are called trough.

Question 11

A Typical Wave -
Wave length -
The wave length lambda is the distance between equivalent points on the wave pattern. It can be from crest to crest or trough to trough

Answer 11

when wave speed is slow, wavelength is long
when wave speed is quick, wavelength is short

Question 12

Amplitude -
It is the maximum displacement from rest or central position in either direction of the wave. It can be thought of as the height of the wave

Question 13

Frequency (f) -
the number of complete vibration occuring in one second. It gives the number of complete waves occurring in one second.

Question 14

1 Kilo Hz = 1000 Hz
1 Mega Hz = 1000,000 Hz

Question 15

1 Hz/Hertz = 1 vibration per s

Question 16

Time period - the time taken to produce one complete wave

Question 17

T = 1/f
F = 1/T

Question 18

w. sp. = f x \
/ \
m/s or cm/s

Question 19

A certain wave has a frequency of 300 Hz and wavelength of 1500 m. Calculate wave speed

Answer 19

Given Wanted
frequency, f = 300 Hz wave speed, w. sp - ?
= 300 vib/s
[ ; ‘ 1 Hz = 1 vib/s]
wave length = 1500 m
Solution
w. sp = f x l
= 300 vib/s x 1500 m
= 450,000 m/s

Question 20

A light wave has a frequency of 4 MHz and speed 500 m/s. Find wave length

Answer 20

Given Wanted
frequency, f = 4 MHz wave length = ?
wave speed, w. sp = 500 m/s
Solution
wave speed = f x l
= wave speed/f
= 500 m/s/4000000 vib/s
= 1/8000m

Question 21

A ripple tank is a special tank for studying waves. In a ripple tank, two types of waves are generated - plane waves and circular waves

Question 22

The bouncing of waves from a straigh barrier is called reflection
The bending of waves is called refraction

Question 23

What happens when plane waves hit a straight barrier

Answer 23

1. The reflected waves are plane waves
2. The reflected waves have the same wavelength
3. The reflected waves leave the barrier at the same angle as the incident waves that hit it

Question 24

plane –> going towards the barrier
reflected waves –> bouncing off the barrier
according to the diagram - lesson 7

Question 25

Incident waves are the incoming waves that hit the barrier Angle of incident (i) - the angle between the incident wave and the normal

Question 26

The waves that bounce of the barrier are known as reflected waves Angle of reflection (r) - the angle between the reflected wave and the normal. On the diagram, an imaginary dotted line is drawn at 90 degree to the surface of the barrier. This line is called normal

Question 27

the angle of incident = angle of reflection i = r

Question 28

90 degree - 40 degree = 50 degree i = 50 r = 50

Question 29

When plane waves hit a curved wave the waves are reflected as circular waves The reflected waves meet and converge at a point called focus

Question 30

When waves travel from deep regions to shallow regions, wave speed slows down, frequency remains same, wave length becomes narrower

Question 31

DIFFERENT TYPES OF WAVES Light travels much faster than sound Light waves can travel through empty space or vacuum. 300000000 m/s --> speed of light 3 x 10 to the power 8 (needed for solving problem) light and heat rays from the Sun travel about 150 million km before reaching the earth Sound waves cannot travel through empty space/vacuum. They need a medium to travel (e.g. water, air, metal, brick, wood)

Question 32

ELECTROMAGNETIC WAVES A special family of waves which have certain properties in common

Question 33

COMMON PROPERTIES O ALL ELECTROMAGNETIC WAVES 1. They are all transverse waves 2. All electromagnetic waves travel at the same speed of light 3. They can travel through empty space (vacuum)

Question 34

In order, shortest - longest wavelengths Gamma rays X rays Ultraviolet Light Infrared Longest radio

Question 35

USES OF ELECTROMAGNETIC WAVES Radio waves UHF - Ultra High Frequency - used for TV signals VHF - Very High Frequency - used in walkie talkies

Question 36

Short wave radio waves are called micro waves and they are absorbed by food. Also used in radio communication

Question 37

Sources of infrared waves are heated substances, metals, furnaces and the sun. These waves are the invisible radiant heat energy that provides warmth

Question 38

Burglar alarms, remote control devices, IR cameras (take picture at night without flash) - all use infrared waves

Question 39

IR lamps use infrared radiation, is red in color, and becomes hot to provide heat energy. It is used in medical purposes for treatment and therapy, and helps muscle cramps.

Question 40

Ultraviolet (uv) radiation (rays) - present in sunlight - the electromagnetic waves give us sun tan, but too much exposure to uv rays can damage our eyes and cause skin cancer - stimulates our skin to produce vitamin D for healthy bones - we get exposed to uv rays due to ozone layer depletion (for CFCs)

Question 41

X - rays - the x rays come out when fast moving electrons smash into a metal target Two types of x rays - short wave length --> highly penetrating, can pass through strong metals like lead, used for broken bone x rays, security machines long wave length --> less penetrating --> used for bone scanning, can go through the layer of flesh

Question 42

X rays can damage/kill living cells in our body, so they are dangerous and we must limit the exposure

Answer 42

(10 diagrams in total..?)

Question 43

Gamma rays They are given off by radioactive materials/particles. These waves are HIGHLY penetrating (can cause and cure cancer). For the highly penetrating rays, they can kill cancer cells deep inside the body. They are used to sterilise hospital/surgical instruments