# WAVES

waves mind map

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WAVES

## 2. PROPERTIES OF WAVES

### 2.1. DESCRIBING WAVES

2.1.1. Amplitude, A

2.1.1.1. Max vertical distance from its rest position

2.1.1.1.1. Unit : Same as length (e.g mm, cm, m)

2.1.2. Period, T

2.1.2.1. Time taken to complete one oscillation (cycle)

2.1.2.1.1. Unit : Same as time (e.g seconds, minutes)

2.1.3. Frequency, F

2.1.3.1. The number of cycles in one second

2.1.3.1.1. Unit : Hertz (per second)

2.1.3.2. 1/Period

2.1.4. Wavelength, λ

2.1.4.1. The horizontal length of one complete cycle of oscillation

2.1.4.1.1. Unit : Same as length (e.g mm, cm, m)

2.1.5. Wavespeed, V

2.1.5.1. The speed of the traveling wave

2.1.5.1.1. Unit : same as speed

### 2.2. TYPES OF WAVES

2.2.1. Mechanical Waves

2.2.1.1. Waves that are transmitted through a medium by vibrating particles

2.2.1.1.1. Examples

2.2.2. Electromagnetic Waves

2.2.2.1. Waves that do not need a medium to travel from one point to another.

2.2.2.1.1. Examples

2.2.3. Transverse Waves

2.2.3.1. Waves where the oscillations of its particles are perpendicular with the direction of the wave.

2.2.4. Longitudinal Waves

2.2.4.1. Waves where the oscillations of its particles are parallel with the direction of the wave.

## 3. EM SPECTRUM

### 3.1. PROPERTIES OF EM WAVES

3.1.1. Travel through a vacuum at the speed of light - 300000 km/s

3.1.2. All are transverse waves

3.1.3. Transfer energy

3.1.3.1. Source loses energy when it radiates EM waves

3.1.3.2. Another material gains this energy when it absorbs it

### 3.2. THE DIFFERENT WAVES

3.2.1. 🌈 VISIBLE LIGHT

3.2.1.1. Red (0.7um), longest

3.2.1.2. Violet (0.4um), shortest

3.2.1.3. All colours travel at 300000 km/s

3.2.2. INFRARED

3.2.2.1. longer wavelength than Visible Light

3.2.2.2. detected by its heating effect on the skin ('radiant heat'/'heat radiation')

3.2.2.3. below 500ºC (hot not glowing)

3.2.2.3.1. emit IR alone

3.2.3. ULTRAVIOLET

3.2.3.1. shorter wavelength than visible light

3.2.3.2. causes sun tan, produce vitamins in the skin, cause skin cancer

3.2.3.2.1. Dark skin is able to absorb more UV, reduces amount reaching deeper tissues

3.2.3.3. some paints + clothes washed in some detergents to fluoresce

3.2.3.3.1. fluorescent lamps

3.2.4.1. longest wavelength in EM spectrum

3.2.4.1.1. lowest energy amount

3.2.4.2. radiated from aerials

3.2.4.2.1. carry information over long distances

3.2.4.3. 3 main categories of Radio Waves

3.2.4.3.1. Long, medium + short radio waves

3.2.4.3.2. VHF & UHF

3.2.4.3.3. Microwaves

3.2.5. X-RAYS

3.2.5.1. Produced when a beam of high-speed electrons hit a metal target in an X-Ray Tube.

3.2.5.2. Smaller wavelengths than UV

3.2.5.3. Short wavelength

3.2.5.3.1. Extremely penetrating

3.2.5.4. Long wavelength

3.2.5.4.1. Less penetrating

3.2.5.5. Dangerous

3.2.5.5.1. Damage living cells - Cause mutation or cancer

3.2.5.6. Dentistry, airport scanners, medicine

3.2.6. GAMMA RAYS

3.2.6.1. Unstable atoms break / lose energy

3.2.6.2. Shorter than X-rays

3.2.6.2.1. <3 x 10^-11 metres

3.2.6.3. More penetrating & dangerous

## 4. LIGHT

### 4.2. SOURCE OF LIGHT

4.2.1. Incandescence

4.2.1.1. Emission of light from hot matter

4.2.2. Luminescence

4.2.2.1. Emission of light during the fall of excited electrons to the ground energy level.

### 4.3. NATURE OF LIGHT

4.3.1. A form of radiation & wave

4.3.2. Transfer energy

4.3.2.1. Energy needed to produce light

4.3.3. Travels in a straight line

4.3.3.1. A ray shows the direction of the path of light

4.3.4. Can travel through vacuum

4.3.5. Speed of light = universal speed limit

4.3.5.1. 300000km/s

### 4.4. LENSES

4.4.1. Convex

4.4.1.1. Thin in centre, spreads light outwards

4.4.2. Concave

4.4.2.1. Thick in centre, bends light inwards

4.4.2.2. Image is smaller, upright & virtual

### 4.5. IMAGES

4.5.1. Real

4.5.1.1. Can be produced on a screen

4.5.1.1.1. Pinhole camera

4.5.2. Virtual

4.5.2.1. Cannot be formed on a screen

4.5.2.1.1. Plane mirror

### 4.6. REFRACTIVE INDEX

4.6.1. Speed of light in medium is known

4.6.1.1. n = c/v

4.6.2. Angle of incidence & angle of refraction is known

4.6.2.1. n = (sin i)/(sin r)

4.6.3. Critical angle is known

4.6.3.1. n = 1/(sin c)

## 5. SOUND

### 5.1. SOUND WAVES

5.1.1. A series of compressions and rarefactions that travel through the air or other medium.

### 5.2. NATURE OF SOUND WAVES

5.2.1. Caused by vibrations

5.2.1.1. Sources all have a vibrating part

5.2.1.1.1. Guitar strings

5.2.1.1.2. Human vocal cords

5.2.2. Longitudinal Waves

5.2.2.1. Oscillates back and forth as the compressions and rarefactions pass through it

5.2.2.1.1. Compression, air pressure increase

5.2.2.1.2. Rarefaction, air pressure decrease

5.2.3. Need a medium to travel

5.2.3.1. Cannot travel in a Vacuum (mechanical waves)

5.2.4. Diffracted

5.2.4.1. Spread through gaps or bend round objects

5.2.5. Refracted

5.2.5.1. Due to change in temperature of the air

5.2.5.1.1. Day

5.2.5.1.2. Night

5.2.6. Reflected

### 5.3. SPEED OF SOUND

5.3.1. Depends on medium

5.3.1.1. 330m/s in air

5.3.1.2. 1500m/s in water

5.3.2. Faster in hot air than cold air

5.3.2.1. More energetic particles = faster

5.3.3. Not affected by atmospheric pressure

### 5.4. ECHOES

5.4.1. Sonar

5.4.1.1. Echolocation

5.4.1.1.1. Locate position of an object by measuring the time taken for an echo to return to its source.

### 5.5. CHARACTERISTICS OF SOUND WAVES

5.5.1. Loudness & Amplitude

5.5.1.1. Greater the amplitude, the louder the sound

5.5.2. Pitch & Frequency

5.5.2.1. Greater the frequency, the higher the pitch