# Waves

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Waves

## 1. Light

### 1.1. Source of Light

1.1.1. Incandescence

1.1.1.1. Emission of light from hot matter.

1.1.2. Luminescence

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

### 1.2. Nature of Light

1.2.1. Transfer energy

1.2.1.1. Example

1.2.1.1.1. Photosynthesis

1.2.1.1.2. Solar Cell

1.2.2. A form of radiation and wave.

1.2.3. Travels in a straight line.

1.2.4. Can travel through a vacuum.

1.2.5. The speed of light is the universal speed limit.

### 1.3. Refraction

1.3.1. Law of refraction

1.3.1.1. sin r = n(sin i)

1.3.2. Refractive index

1.3.2.1. Speed of light in a vacuum/speed of light in a medium.

1.3.3. Formulas

1.3.3.1. n=c/v

1.3.3.1.1. If the speed of light of medium is known.

1.3.3.2. n= sin i/sin r

1.3.3.2.1. If angle of incidence and angle of refraction is known.

1.3.3.3. n= 1/sin c

1.3.3.3.1. If critical angle is known.

### 1.4. Reflection

1.4.1. Law of Reflection

1.4.1.1. i = r

1.4.2. Characteristics of Reflected Image

1.4.2.1. Virtual

1.4.2.2. Laterally inverted

1.4.2.3. Same size as object

1.4.2.4. Object and image at an equidistant

1.4.2.5. The line joining the object and image being perpendicular to the mirror.

### 1.5. Lenses

1.5.1. Convex

1.5.1.1. Solves issue of farsightedness

1.5.2. Concave

1.5.2.1. Solves issue of shortsightedness

## 2. Sound

### 2.1. How it travels

2.1.1. Rarefaction

2.1.1.1. Region where the particles are far apart.

2.1.2. Compression

2.1.2.1. Region where the particles are close together.

### 2.2. Terms

2.2.1. Pitch and Frequency

2.2.1.1. The higher the frequency, the higher the pitch.

2.2.1.2. The normal human ear can hear ranging from 20Hz to 20kHz

### 2.3. Nature of Sound Waves

2.3.1. Caused by vibrations

2.3.2. Longitudinal waves

2.3.3. Requires a medium to travel

2.3.4. Able to be Refracted, Diffracted and Reflected.

## 3. Properties of Waves

### 3.1. Describing waves

3.1.1. Amplitude

3.1.1.1. Maximum or minimum displacement from the origin.

3.1.2. Frequency

3.1.2.1. Number of complete oscillations in one second.

3.1.3. Wavelength

3.1.3.1. The horizontal length of one complete cycle of oscillation.

3.1.4. Wave Speed

3.1.4.1. The speed of the travelling wave

### 3.2. Types of waves

3.2.1. Mechanical Waves

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

3.2.2. Transverse Waves

3.2.2.1. Vibration of particles is perpendicular to its propagation (forward).

3.2.2.1.1. Example

3.2.3. Longitudinal Waves

3.2.3.1. Vibration of particles is parallel to its propagation.

3.2.3.1.1. Example

3.2.4. Electromagnetic Waves

3.2.4.1. Waves that do not require a medium to move through the oscillation of perpendicular magnetic and electric fields.

3.2.4.1.1. Example

### 3.3. Phenomenon of Wave

3.3.1. Refraction

3.3.1.1. Phenomenon when light travels in 2 different mediums.

3.3.2. Reflection

3.3.2.1. Occurs when the waves return after encountering an object.

3.3.3. Diffraction

3.3.3.1. The bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture.

## 5. EM Spectrum

### 5.1. Infrared (IR)

5.1.1. Infrared rays have longer wavelength than visible light (from about 0.7um to 0.1um).

5.1.2. Our bodies detect infrared radiation by its heating effect on the human skin. Sometimes called 'radiant heat' or 'heat radiation'.

5.1.3. Anything which is hot but not glowing (below 500°C) emits IR alone.

5.1.4. Infrared sensors are used on satellites and aircraft for weather forecasting, monitoring of land by assessing heat loss from buildings and locating victims of earthquakes.

### 5.2. Visible Light

5.2.1. Red light has the longest wavelength, which is about 7 um.

5.2.2. Violet has the shortest wavelength about 4 um.

5.2.3. All color travels with the same speed of 3 x 10^8 in air (or in vacuum).

### 5.3. Ultraviolet

5.3.1. Ultraviolet (UV) rays have shorter wavelengths than light (from about 0.1um to 0.4um).

5.3.2. Some insects like bumblebees can see them.

5.3.3. Causes sun tan and produces vitamins in the skin but can penetrate deeper, causing skin cancer.

5.4.1. 3 Types of Radio Waves

5.4.1.1. Long, medium and short radio waves

5.4.1.2. VHF and UHF

5.4.1.3. Microwaves

5.4.3. These waves can range from 1cm to greater than 1km.

5.4.4. The energy of radio waves is much lower than the energy of other types of electromagnetic radiation.

5.4.5. They are radiated from aerials and used to carry information over long distances.

### 5.5. X-Rays

5.5.1. X-rays are produced when a beam high speed electrons hits a metal target in an X-ray tube.

5.5.2. X-Rays have a smaller wavelength than UV.

5.5.3. Widely used in dentistry, security machines, or even to treat cancer cells.

### 5.6. Gamma Rays

5.6.1. Gamma rays come from radioactive material. They are produced when the nuclei of an unstable atoms break up or lose energy.

5.6.2. They have shorter wavelengths than X-rays.

5.6.3. Gamma radiation consists of photons with a wavelength less than 3x10^-11 meters.

5.6.4. Gamma rays are more dangerous and penetrating than X-rays. They are used to kill cancer cells, sterilizing food and surgical equipment.