1. EM Spectrum
1.1. All EM waves travel at the same speed through a vacuum, at 300000km/s.
1.2. They are transverse waves.
1.3. They transfer energy. A source loses energy when it transfers EM waves and gains energy when it absorbs EM waves.
1.4. Types of waves in the EM Spectrum:
1.4.1. Visible light (0.4-0.7μm)
1.4.1.1. Only type of light that is visible to the human eye
1.4.1.2. ROYGBIV
1.4.1.3. All colours travel at the same speed through air at 3x10^8 m/s
1.4.1.4. A form of radiation and wave
1.4.1.5. The universal speed limit
1.4.2. Infrared (0.7μm-0.01mm)
1.4.2.1. Radiated by hot objects starting at around 500ºC.
1.4.2.2. Can be detected by our body as it heats our skin up.
1.4.2.3. Can be used to detect objects that radiate heat or to dry things.
1.4.2.4. Used in remote controls for sending signals.
1.4.3. Ultraviolet (0.1-0.4μm)
1.4.3.1. Can be harmful to humans if exposed to skin for long periods of time.
1.4.3.1.1. You can reduce exposure by wearing clothing covering larger areas of skin or by applying sunscreen.
1.4.3.2. Causes production of vitamins in human skin.
1.4.3.3. Can causes fluorescent paints and clothes washed in some detergents to fluoresce.
1.4.4. Radio Waves (1cm->1km)
1.4.4.1. Have the longest wavelengths in the EM spectrum.
1.4.4.2. Carry low amounts of energy compared to other waves.
1.4.4.3. 3 main categories of radio waves:
1.4.4.3.1. Long, Medium and Short Waves
1.4.4.3.2. VHF and UHF Waves
1.4.4.3.3. Microwaves
1.4.5. X-rays
1.4.5.1. Produced when a beam high-speed electrons hits a metal target in an X-ray tube.
1.4.5.2. Can pass through many materials that absorb visible light.
1.4.5.3. Short-wavelength X-rays are extremely penetrating. They can be stopped by dense metals such as lead.
1.4.5.4. Long-wavelength X-rays are less penetrating.
1.4.5.4.1. Long-wavelength X-rays can be used in radiographs because the waves only pass through skin and not bone.
1.4.5.4.2. Can also be used in security machines, to detect the presence of illicit items.
1.4.5.5. Even so, all wavelengths of X-rays are harmful and can cause mutations in cells.
1.4.5.5.1. However, concentrated beams of X-rays can be used to kill cancer cells.
1.4.6. Gamma rays
1.4.6.1. Are radiated from radioactive material.
1.4.6.2. Consists of photons with a wavelength less than 3x10^−11 meters.
1.4.6.3. More dangerous than X-rays.
1.4.6.4. Used in cancer treatment and sterilisation of surgical instruments.
2. Lenses
2.1. Convex
2.1.1. Bends light inwards
2.1.2. thickest in the centre
2.2. Concave
2.2.1. thinnest in the centre
2.2.2. spreads light out
2.3. Properties of lenses:
2.3.1. Optical centre, c
2.3.1.1. centre of a lens
2.3.2. principal axis
2.3.2.1. line through c perpendicular to the lens
2.3.3. focal point, f
2.3.3.1. The point on the principal axis where all rays parallel to axis converge to it after passing through a convex lens or appear to diverge from it after passing through a concave lens
2.3.4. focal length,f
2.3.4.1. distance between c and f
3. Properties of waves
3.1. Can be refracted, reflected and diffracted
3.1.1. Refraction: Occurs when the wave slows down and changes direction. Can be observed when a wave moves through one medium into another.
3.1.1.1. Can be observed when you pass white light through a prism. This reveals the spectrum of visible light.
3.1.2. Diffraction: When a wave bends round the sides of an obstacle or when the wave spreads out as it passes through a gap.
3.1.3. Reflection: When a wave bounces off the surface of an object.
3.1.3.1. Allows us to see the objects around us, as visible light bounces off the objects and into our eyes.
3.2. Can undergo interference
3.2.1. When other waves "cross" into another wave, the wave may slightly or fully change its direction of travel, as well as lose energy.
4. What is a wave?
4.1. A wave is a travelling disturbance from an oscillating source. A wave can transfer energy from an object to another without transferring matter.
4.2. Two types of waves: Longitudinal, Transverse
4.2.1. Transverse: Particles move perpendicular with the direction of the wave.
4.2.2. Longitudinal: Particles move parallel to the direction of the wave.
4.3. Classificaiton of waves: Mechanical waves, Electromagnetic waves.
4.3.1. Mechanical waves need a medium to be transmitted, while EM waves do not.
5. Parts of a wave diagram
5.1. Amplitude,g: The maximum vertical distance from its rest postion. Relative to loudness of the sound. (unit: cm)
5.2. Period,T: The time it takes for one oscillation. (unit: time)
5.3. Frequency,f: The number of oscillations in 1 second. (unit: 1/period, Hz)
5.4. Wavelength,λ: The horizontal length of one complete cycle.
5.5. Wave speed,v: The speed of the travelling wave
5.6. v=λf
6. Sound
6.1. Series of compressions and rarefactions that travel over air or other mediums.
6.2. Properties of sound waves
6.2.1. Caused by vibrations
6.2.2. Are longitudinal
6.2.3. Require a medium to travel through
6.2.4. Can be diffracted
6.2.5. Can be refracted
6.2.6. Can be reflected
6.3. Travels at 330 m/s through air and at 1500 m/s through water.
6.3.1. Speed of sound depends on medium and temperature, but atmospheric pressure does not affect it.
6.3.2. The hotter the medium is, the faster sound travels.
6.3.3. How to measure speed of sound?
6.3.3.1. Set two microphones apart at a recorded distance, connect the microphones to a timer, which is set to start when the sound is detected by the first microphone and stop when the second microphone detects the sound.
6.3.3.2. Then, make a sound at one end of the first microphone using a hammer.
6.3.3.3. Take note of the time recorded.
6.3.3.4. Then, divide the recorded distance by the time taken.
6.4. Echoes
6.4.1. Occurs when a sound wave is reflected off a hard surface.
6.4.1.1. Can be used for detecting objects in enclosed spaces, or in oceans.
6.4.2. Can be reduced by using sound insulation,
6.4.2.1. Objects such as carpets, curtains and foam can be used.
6.5. Loudness is directly related to amplitude. The higher the amplitude, the louder the sound.
6.6. Pitch is directly related to the frequency of the sound. The higher the frequency, the higher the sound.
7. Types of images
7.1. Real images
7.1.1. An image that can be produced on a screen.
7.2. Virtual images
7.2.1. Images that cannot be produced on a screen.
7.2.1.1. Images in plane mirrors are virtual images.
7.2.1.2. Images in plane mirrors are also laterally inverted.
7.2.1.3. Images in plane mirrors are also the same size as the object.
7.3. Images formed by concave lenses are always smaller, upright and virtual
8. Refraction+reflection
8.1. Occurs when light passes from one medium into another. A strong refracted ray and a weak reflected ray are produced.
8.1.1. Critical angle,c
8.1.1.1. The angle at which the angle of refraction is 90º
8.1.1.2. Different materials have different critical angles.
8.1.2. Total internal reflection
8.1.2.1. Occurs when the angle of incidence is grater than the critical angle, c.
8.1.2.2. When this occurs, light is totally reflected back into its own medium and does not exit the medium.
8.1.2.3. Total internal reflection is used in optical fibre cables.
8.1.2.3.1. Optical fibre cables have visible light reflected through them. They are used to send information.
8.1.2.3.2. Can be used in endoscopes or in network cables.
8.2. Refractive Index
8.2.1. speed of light in vacuum/ speed of light in medium
8.2.2. n=c/v
8.2.2.1. n= sin i/sin r
8.2.3. Higher refractive index means light is bent more as it passes through that material.
8.2.4. formula for refractive index when critical angle is given:
8.2.4.1. n=1/sin c