Science Chapter 5

Dispersion (refraction)

(colour Chart)

Primary, Secondary colour in light

(picture)

Colours in the spectrum

- Red, Green and Blue - Primary colours, If primary colours can be seen then secondary colours are produced. (Cyan, Yellow, Magenta - Secondary Colours)

Primary, Secondary colour in pigment

(picture)

F.M & A.M Radio Waves

- Each radio station broadcasts signals at a particular frequency, which you receive when you tune your radio to this frequency. - AM and FM radio waves involve using a wave called a carrier wave. - The audio signal is transmitted from the microphone in the radio station. - After being detected by the antenna of a radio, the carrier wave is subtracted from the signal, leaving only the original signal. This signal is amplified and directed to the speakers, where it is converted to sound once more - FM signal has a wavelength of around 3 metres, - AM signal has wavelengths longer than 100 metres. The longer AM radio waves can bend around large obstacles like buildings, trees and hills more easily than the smaller FM waves. - This bending around obstacles is called diffraction. AM signals travel further than FM signals, but they are of lower quality and are more likely to suffer from interference.

Wave Properties - Frequency - Wave Length

- Frequency: the number of waves produced each second (measured in hertz (Hz) ) - Wave Length: the distance between successive waves. (represented by the greek symbol λ (lambda) & measured in meters.

Gamma Rays

- Gamma rays have a wavelength of about one-hundred-billionth of a metre. - Only a thick sheet of lead or a concrete wall will stop them. Gamma rays are produced in making nuclear power and nuclear bombs, and can be detected with photographic film or a machine called a Geiger counter. - Due to their high energy, gamma rays can interact with matter. - Gamma rays can free electrons from their atoms, which in turn ionise or remove electrons from surrounding atoms. - This ability is used to target and kill cancer cells in patients undergoing radiotherapy. - Gamma rays are also useful in medical diagnosis. In the technique of positron emission tomography (PET), a patient is injected with small amounts of a short-lived radioactive material. This emits gamma rays, are detected by a PET scanner/camera. This data is converted using computer analysis into a three-dimensional image.

Infraed Radiation

- Heat is transferred from the Sun to us as infrared radiation. Infrared rays are given this name because they are next to red light in the visible spectrum. 'Infra' means below, and infrared radiation has a lower frequency than red light - You cannot see this radiation, but can detect its presence as warmth on your skin. - All objects with a temperature above 0 emit infrared radiation. The hotter something is, the more infrared radiation it emits. - Infrared radiation can be detected using an infrared camera.

Filters - Absorption and reflection

- Is when an object absorbs all colours except for the colour it reflects (e.g a red apple absorbs all colours except red light, therefore we see red.)

Microwaves

- Microwaves have shorter wavelengths than radio waves and are used in radar and communication systems. - Shorter microwaves with wavelengths of about 0.1 mm are used in cooking. Microwaves are absorbed by water, fats and sugars in food, causing the food molecules to vibrate and heat up. Because the heating occurs inside the food without warming the surrounding air, the food cooks quickly but sometimes unevenly. Glass, paper and many plastics don't absorb microwaves, and metal reflects microwaves.

Remote Sensing Types

- Most remote-sensing techniques detect radiation that is naturally emitted or reflected from the area being studied. In these techniques, radiation such as solar radiation or infrared radiation of the Earth is analysed. Using natural reflection or emission is called passive remote sensing. - Another form of remote sensing is called active remote sensing. In this case, radiation such as radio waves or microwaves is directed onto a target, and the radiation that is deflected from the target is detected and analysed. This technique is unaffected by dense cloud cover and can be done at night. It is used in urban mapping, rice mapping, flood mapping, agricultural monitoring and snow mapping.

Polarisation

- Polarisation and interference of lightLight travels as an electromagnetic wave in three dimensions. If you wear a pair of Polaroid sunglasses on a sunny day, you can still see but the lenses absorb much of the light energy that hits them. - This happens because light has been polarised. This means that only waves vibrating in a certain direction are allowed through the filter, while those vibrating in other directions are absorbed. - Filters like these are used to manufacture the polarising lenses of sunglasses. They absorb much of the incoming light energy, but allow enough light through for us to still see clearly

Radio Waves

- Produced through vibrating or oscillating electrons in a transmitting aerial. - Have the longest wavelengths of all types of electromagnetic radiation. ( range from: few metres to a few kilometres.) These are the lowest-energy form of electromagnetic radiation.

Short-wave and Long-wave radio Signals

- Short-wave and long-wave radio signals are also used in communications. - Short-wave radio signals (wavelength about 30 m) can be transmitted long distances by beaming the waves upwards at an angle. - The waves are reflected back to Earth by a layer of the atmosphere called the ionosphere, far away from where the transmitter is locate

Wave Motion - What is it - Two types

- The transfer of energy without matter is called wave motion 1. transverse wave 2. longitudinal wave

The Visible Spectrum

- The visible spectrum is the range of colours that combine to form white light. Visible light is just a small band of the frequencies that make up the electromagnetic spectrum. This is the band of electromagnetic radiation that our eyes can detect. The world would look very different to us if we had the UV vision of a bee, or the infrared vision of a snake

Ultraviolet light

- Ultraviolet (UV ) light is radiation with a higher frequency than violet light. - Sunlight contains UV light in addition to infrared and visible light. Your body needs some exposure to UV light to produce vitamin D. Although you cannot see UV light, it can tan or burn your skin. - High exposure to UV light can cause skin cancers such as melanoma. UV light can also cause cataracts in your eyes. -- Approved sunglasses and sunscreens can offer us some protection from these rays. - Some substances fluoresce when hit by UV light = This means they absorb UV light and emit visible light. White paper, teeth whiteners and some laundry powders add fluorescent particles to take advantage of this property. The particles make the paper, teeth or clothes appear brighter. - UV light is also used to sterilise objects

Visible Light

- Visible light from the Sun helps us to make sense of our world, and is also essential for much of the life on Earth. - Plants absorb light and use the energy to make the carbohydrates, fats, proteins, vitamins and other materials that humans and other animals depend on. - Visible light, or white light, consists of different colours. You can see this when you view a rainbow. - Each colour has a different wavelength and frequency. - Blue light has the shortest wavelength and the highest frequency; - Red light has the longest wavelength and the lowest frequency.

X - rays

- X-rays have great penetrating power and so are used to investigate the structure of objects and to find flaws in metals. - This radiation has such high energy that it can damage cells and tissues, and also the genetic material inside cells. - X-rays are produced when electrons hit a metal surface. This happens inside an X-ray tube. X-rays are used in radiology, to produce images of bones. - They are also used in radiotherapy, in which X-rays are targeted at cancer cells to kill them or stop them from multiplying. - When a patient undergoes a computed tomography (CT) scan, the X-ray sources and detectors rotate around the person. Computers then analyse the data from the CT scanner to create images of organs in the body. - Luggage scanners in airports use X-ray devices to examine baggage.Because of the high energy of X-rays, it is important that people who work with them use protective lead shields and monitor their exposure levels.

The electromagnetic spectrum

Radio waves-(f.m &a.m Radio), Microwave, Inferred rays, Visible light, Ultraviolet waves, X-ray, Gamma Ray,

Analog vs Digital

Some mediums, such as the copper wires connected to landline phones, are designed to carry an analogue signal. The voltage of such a signal is determined by the speaker's voice. Analogue signals are limited as they suffer from signal loss and interference as they travel. Most communications systems that we use regularly, such as television, computer and iPod, rely on a digital signal. A modem connects a computer to a telephone line and converts the digital computer signal into an analogue signal that the phone line transmits. This process of coding the signal into a different format is called modulation. Our mobile phone network is digital, as is the music we listen to on CDs or DVDs. A digital signal can still be read even when interference disturbs the message

The wave equation

The equation can be rearranged to calculate frequency: f = v/λ It can also be rearranged to calculate wavelength: λ = v/f