Section 3 d) Summary

Waves can be reflected, refracted and diffracted, whether they're transverse or longitudinal.

Sound waves can be measured using a device called an oscilloscope and a microphone. The microphone is connected into the oscilloscope, a sound made, and from the tracing made the frequency, amplitude, time period and wavelength can be calculated.
Louder sounds have a higher amplitude, and more high-pitched sounds have a higher frequency.

Reflection
The law of reflection says that the angle of incidence = the angle of reflection

i = r

This principle can be applied to a phenomenon known as Pepper's ghost, where lights and reflections are used to project a virtual image.

One light shines onto the background, lighting it up so the viewer can see it through the glass. The other light shines onto an image, hidden from view. The light is reflected off of this image, and travels to the glass, where it is reflected and the viewer sees it. The reflection merges with the background, so appears to be there and not just a reflection. This is called a virtual image.
This concept can also be demonstrated in a more simple manner:

The glass is equidistance from the candles, so when the light from the front candle is reflected it appears to be on the unlighted candle.

Sound experiment:

1. Measure 100 metres from a wall, and stand there and clap with clapping blocks. Every time you hear the echo of the previous clap, clap again.
2. Once you have a steady rhythm, time how long it takes for the time periods of 10 claps (count 11 claps) 
3. Divide this time by 10 to find the time for 1 clap, then divide double the distance (200 m) by this number (you must double it because the wave travels the distance to the wall and back).

This will give you the speed of sound in air, but is also affected by human reaction times so will not give a totally accurate result.

Total internal reflection (finding the critical angle):

1. Shine a ray into a semi circular prism (this is ideal, because you can shine at the mid-point of the flat side without being refracted the first time due to the shape having normals at all angles)
2. Shine it at the mid-point from a range of different angles, starting with a smaller angle of incidence, and gradually moving it around, until the ray is in line with the flat edge. This is the critical angle: the last point at which the light is reflected. 
3. Once the angle is greater than the critical angle, it will become totally internally reflected. 

Critical angle can be calculated with this formula: sin c = 1 / n 

Total internal reflection is useful in optic cables among other things. It allows the information to be transferred long distances without being lost, all of the light is reflected. This concept is also used in jewellery and cutting jewels such as diamonds. By creating total internal reflection, they reflect light more and are more 'sparkly'. 

Refraction

Refraction is when the direction of a wave changes as it changes from one medium to another.
You can see this when you put a straw in water, it appears bent or broken.

We can see how different objects and media refract objects through investigations.

Finding the refractive index of glass
1. Using a rectangular glass block, and trace its outline onto a piece of paper. Create a series of lines to create different angles about a normal.
2. Shine a line/ray of light from a ray box along each line, and mark the emergent line with two x's, and connect the line to the normal, and then to the angle of incidence.
3. Measure each of the angles of refraction in comparison to the angle of incidence, and use
n = sin i / sin r
for each, and find the average of n to try to erase inaccuracies.

This same experiment can be done with different shaped blocks to see how this affects it, or different media (e.g. plastic)


Diffraction

Diffraction is the spread of waves beyond a barrier. This can be seen with waves at the beach, after passing through a gap

This effect happens in the same manner with sound and light waves. For example, when a door is opened into a dark room, we see the light spread.
 

Diffraction is increased when the ratio of gap size to wavelength is balanced so the gap size is smaller and the wavelength is larger.

Diffraction doesn't just happen through gaps, though, it also happens when passing an edge.

Signals: Analogue vs. Digital

Signals can be digital or analogue, the difference being that analogue has continuous variables and digital having two fixed settings, on and off or 0 and 1.

Advantages and disadvantages:

• Digital signals have a wider bandwidth and can carry more information
• Digital can be more easily restored if distorted
• Analogue signals are near impossible to restore if badly distorted. 
• Analogue signals have an infinite range of data
• Analogue signals are easy to process
• Analogue signals are easily distorted
• Digital signals travel faster
• Digital signals are more complicated to process.