1. properties of waves
1.1. reflection
1.1.1. waves reflect off smooth, plane surfaces
1.1.2. angle of incidence = angle of reflection
1.1.3. frequency, wavelength and speed are all unchanged
1.2. refraction
1.2.1. speed of wave changes when it enters a new medium
1.2.2. if the wave enters a more optically dense medium, its speed decreases and it bends towards the normal and the opposite happens when it enters a less dense medium
1.2.3. frequency stays the same but wavelength changes
1.3. diffraction
1.3.1. waves spread out when they go around the sides of an obstacle or through a gap
1.3.2. frequency, wavelength and speed are unchanged
1.4. .
1.4.1. wavelength
1.4.1.1. the distance between a point on one wave and the same point on the next wave
1.4.2. amplitude
1.4.2.1. the distance from the equilibrium position to the maximum displacement
1.4.3. frequency
1.4.3.1. the number of waves that pass a single point per second
1.4.4. speed
1.4.4.1. the distance travelled by a wave each second
1.4.4.2. Speed is related to frequency and wavelength by: 𝒔𝒑𝒆𝒆𝒅 = 𝒇𝒓𝒆𝒒𝒖𝒆𝒏𝒄𝒚 × 𝒘𝒂𝒗𝒆𝒍𝒆𝒏𝒈𝒕𝒉
2. electromagnetic spectrum
2.1. properties
2.1.1. transverse waves
2.1.2. do not need a medium
2.1.3. travel at the speed of 3.0x10^8 m/s in vacuum and approximately the same in air
2.1.4. groups of waves go in ascending order of decreasing wavelength and increasing frequency
2.1.4.1. Radio waves
2.1.4.1.1. used for radio and television communications. They have a long wavelength and are reflected by the ionosphere.
2.1.4.2. Microwaves
2.1.4.2.1. used for satellite communication and in microwave oven. They pass through the ionosphere and penetrate deep into food.
2.1.4.2.2. Microwaves can cause internal heating of body tissues.
2.1.4.3. Infrared radiation
2.1.4.3.1. used in remote controllers and infrared cameras.
2.1.4.3.2. Infrared radiation can cause skin burns.
2.1.4.4. Visible light
2.1.4.4.1. used in fibre optics.
2.1.4.5. Ultraviolet light
2.1.4.5.1. used in tanning beds.
2.1.4.5.2. Too much exposure to ultraviolet light skin increases the risk of skin cancer.
2.1.4.6. X-rays
2.1.4.6.1. used in medical imaging and in security as they can penetrate material easily.
2.1.4.6.2. X-rays and gamma rays are ionising radiation that can cause mutations leading to cancer.
2.1.4.7. Gamma rays
2.1.4.7.1. used in medical treatment due to its high energy.
2.2. .
3. types of waves
3.1. transverse
3.1.1. has peaks and troughs
3.1.2. vibrations are at right angles to the direction of travel
3.1.3. .
3.1.4. Light is an example of transverse waves
3.1.4.1. reflection
3.1.4.1.1. .
3.1.4.1.2. total internal reflection
3.1.4.2. refraction
3.1.4.2.1. the refractive index (n) of a medium is the ratio between the speed of light in a vacuum and the speed of light in the medium
3.1.4.2.2. dispersion
3.1.4.2.3. optical fibres
3.1.4.3. Converging lens
3.1.4.3.1. transparent block which brings light rays together at a point
3.1.4.3.2. real images
3.1.4.3.3. virtual imagen
3.1.4.3.4. same size images
3.1.4.3.5. enlarged images
3.1.4.3.6. diminished images
3.2. longitudinal
3.2.1. consists of compressions (particles pushed together and rarefactions (particles moved apart)
3.2.2. vibrations are parallel as the direction of travel
3.2.3. mediums are needed to transmit them
3.2.4. .
3.2.5. sound is an example of a longitudinal wave
3.2.5.1. the greater the amplitude, the louder it is
3.2.5.2. the greater the frequency, the higher its pitch
3.2.5.2.1. The range of audible frequencies for a healthy human ear is 20 Hz to 20000 Hz.
3.2.5.2.2. Ultrasound is sound with a frequency greater than 20000 Hz
3.2.5.3. speed of sound
3.2.5.3.1. in air
3.2.5.3.2. in water
3.2.5.3.3. in steel