Waves

1) Waves transfer energy from one point to another without transferring matter

In transverse waves (e.g. water waves, all electromagnetic waves), the vibrations of the particles are perpendicular to the wave direction 

• crests
• troughs
• wavelength = distance between two successive crests/troughs
• amplitude = vertical distance between the crest/trough and the “middle”
• light waves travel slower in a denser medium

In longitudinal waves (e.g. sound waves), the vibrations of the particles are in the same direction as the wave

• compressions
• rarefactions
• wavelength = distance between two successive compressions/rarefactions
• amplitude = vertical distance between the “top” of the wave and the “middle”
• sound waves travel faster in a denser medium

2) Refraction (the more complicated ones)

Convex lens

White light through a glass prism

Refractive Index of Light 

• Speed of light in air ÷ speed of light in medium
• Refractive index for glass is 1.5, for water is 1.33 (means that light will be bent more in glass than in water)

3) Critical Angles and Total Internal Reflection

• angle of incidence = critical angle… light travels along surface of medium
• angle of incidence > critical angle = light is reflected back into the denser medium

Optical Fibres

• made of glass
• used in telecommunications (transmit data/voice/images, as light signals, over long distances)
• used in medicine

Advantages: 

• cheaper than copper wires
• thinner than copper wires (more fibres per cable diameter so more information transmitted)
• clearer signal (electrical signals in copper wires interfere with other copper wires in the same bundle – optical fibres carry light signals so no interference among cables in a bundle)
• signals travel much farther than in copper signals, with the same amount of power

4) Diffraction

5) Sound waves: no medium, no sound

• In air, disturbances are passed from air molecule to air molecule
• In a vacuum, there is no medium to carry the disturbances produced by the vibrating object

6) Musical notes

• Higher frequency = higher pitch
• Higher amplitude = higher volume i.e. louder
• Quality/timbre depends on waveform

Fieldwork: Water Testing

pH level

Collect a water sample. Dip a dry strip of litmus paper into the sample. Leave for a few minutes or until the litmus paper has changed colour. Compare the new colour of the litmus paper to the pH colour chart (any number below 7 is acidic, any number above is alkaline).

Nitrate level

Collect a water sample. Put about 2.5ml of the water into a test tube. Add an equal volume of nitrate-reducing reagent. Cover and shake the test tube until the contents are fully combined. Observe the colour of the mixture and compare it to the colour chart in the nitrate testing kit – from this you can approximate the nitrate concentration of the water sample in mg/L.

Turbidity

Secchi disk method (in a deeper part of the river)

Slowly lower the Secchi disk into the water and stop just when you can no longer see it. Record the depth (indicated by marks on the rope). Slowly raise the disk until it can just be seen again. Record the depth. Find the mean of these two depths to determine the Secchi depth.

Reagent test method

Collect a water sample. Compare the turbidity to a control solution of equal volume. Gradually add a turbidity reagent to the control sample until it is visually identical the water sample. A value can be determined in standard Jackson Turbidity Units.

Odor

Threshold Odour Test:

Collect a water sample. Add odorless water to the sample and stop when the sample itself is odorless. The last dilution before the sample becomes odorless determines the Threshold Odor Number (TON), which measures how much odor was present.