General Properties of Waves

Waves are vibrations that transfer energy from place to place without matter (solid, liquid or gas) being transferred. 

Some waves must travel through a substance. The substance is known as the medium and it can be solid, liquid or gas. Sound waves and seismic waves are like this. They must travel through a medium, and it is the medium that vibrates as the waves travel through/

Other waves do not need to travel through a substance. They must be able to travel through a medium, but they do not have to. Visible light, infared rays, microwaves and other types of electromagnetic radiaiton are like this. They can travel through empty space. Electrical and magnetic feids vibrate as the waves travel.

Transverse Waves 

• In transverse waves, the vibrations are at right angles to the direction of travel and enery transfer.
• Light and other types of electromagnetic radiation are transverse waves. 
• All types of electromagnetic waves travel at the same speed through a vaccum, e.g. space

Longitudinal Waves

In longitudinal waves, the vibrations are alone the same direction as the direction of travel and energy transfer.

Sound waves and waves in a stretched spring are longitudinal waves. P waves (relatively fasrt moving lonigtudinal seismic waves that travel through liquids and solids) are also longitudinal waves.

Longitudinal waves show area of compression and rarefaction. 

Amplitude:

As waves travel they set up patterns of disturbance. The amplitude of a wave is its maximum disturbance from its undisturbed position. The amplitude is not the distance from the top and bottom of the wave.

Wavelength:

• The wavelength of a wave is the distance between a point on one wave and the same point on the next wave 
• It is often easiest to measure this from the crest of one wave to the crest of the next wave but it doesnt matter as long as it is the same point in each wave.

Frequency 

The frequency of a wave is the number of waves produced by a source each second. It is also the number of waves that pass a certain point each second.

The unit of frequency is the hertz (Hz)/Kilohertz(kHz)/megahertz(MHz) and gigahertz (GHz) to be used when waves have very high frequencies.

• v is the wave speed in metres per second, m/s
• f is the frequency in hertz, Hz
• λ (lambda) is the wavelength in metres, m.

All waves obey this wave equation. 

e.g.

A wave with a frequency of 100 Hz and a wavelength of 2m travelts at 100x2 = 200m/s

Refraction

Sound waves and light waves change speed when they pass across the boundary between two substances with different desities, such as air and glass. This causes them to change direction and this effect is called refraction.

Refraction doesnt usually happen if the waves across the boundary at an angle of 90 degrees (called the normal) - in that case they carry straight on.

Diffraction

When waves meet a gap in a barrier, they carry on through the gap. However, the waves spread out to some extent into the area beyond the gap. This is called diffraction

The extent fo the spreading depends on how the width of the gap compares to the wavelength of the waves. Significant diffraction only happens when the wavelength is of the same order of magnitude as the gap e.g.

• A gap simialr to the wavelength causes a lot of spreading with no sharp shawdow e.g. doorway
• A gap much larger than the wave length causes little spreading and a sharp shadow 

An angle of incidence equals the angle of reflection

• The normal is a line drawn at right angles to the reflector
• The angle of incidence is between the incident (incoming) ray and the normal 
• The angle of reflection is between the reflected ray and the normal 

Smooth surfaces produce strong echoes when sound waves hit them, and they can act as mirros whem light waves hit them.

• Appear to come from a point behind the mirror
• Be focused to a point, for example sunlight reflected off a concave telescope mirror.

Sound waves are longitudinal waves. Their vibrations occur in the same direction as the direction of travel. Sound waves can only travel through a solid, liquid or gas.

• Vibrations
• The greater the amplitude, the louder the sounds
• The greater the frequency the higher the pitch 

• Range of Human hearing:

The electromagnetic spectrum is a continuous range of wavelengths. The types of radiation that occur in different parts of the spectrum have different uses and dangers, which depend on their wavelength and frequency.

White light can be split up using a prism to form a spectrum. The light waves are refracted as they enter and leave the prism. The shorter the wavelength of the light, the more it is refracted. 

As a result, red light is refracted the least and violet light is refracted the most, causing the coloured light to spread out to form a spectrum.

Visible light is just one type of electromagnetic radiation. There are various types of electromagnetic radiation, some with longer wavelengths than visible light and some with shorter wavelengths than visible light.

energyfrequencywavelengthtype of electromagnetic typical use lowest lowest longest radio waves television signals microwaves cooking, mobile phones infrared optical fibre communication visible light seeing ultraviolet detecting forged bank notes X-rays medical images of bones highest highest shortest gamma radiation killing cancer cells

Radio Waves

A radio programme reciever does not need to be directly in veiw of the transmitter to recieve programme signals. Diffration allows low-frequency radio waves to be recieved behind hills, although repeater stations are often used to improve the quality of the signals.

The lowest frequency radio waves are also reflected from an electrically charged layer of the upper atmosphere called the ionosphere.

Microwaves 

Microwave radiation can also be used to transmit signals such as mobile phone calls. Microwave transmitters and recievers on buildings and masts communicate with the mobile telepohones in their range. Some people tink that mobile phones which transmit and recieve microwaves may be a health risk.

Certain microwave radiation pass through the earths atmospher and can be used to transmit information to and from satellites in orbit. 

Visible Light 

Visible light is the light we can see. It allows us to communicate with one another through books, hand signals and video. E.g. The use of visible light needs the transmitter and reciever to be in the light of sight.

Cameras let us record still pictures and movies, and photography is an important use of visible light. 

Infrared 

We cannot see infrared radiation, but we can feel it as heat energy. High intensity infrared is used in heaters, toasters and grills and it can cause burns. Infrared sensorts can detect heat from the body e.g. Security lights, burglar alarms

Infrared radiation is also used to transmit information from place to place including:

A remote controls for televeision sets and DVD players, data links between computers