3d) Light and Sound (Waves)

Light Waves 

Transverse 

Reflection: - Allows us to see most objects
                   - Light reflects from each surface

Angle of INCIDENCE = Angle of REFLECTION 

A virtual image is formed when light rays bounce off a mirror. Object appears to be in a different place.

1. Image same size as object 
2. As far behind 
3. Formed from diverging rays 

Refraction: Change of direction which is caused because the speed of light slows down 

Refraction index of a material indicates indicates how strongly the material changes the direction of light 

Snell's Law 

Refractive index n = sin i/ sin r 

i = angle of incidence 

r = angle of reflection 

Another Rule

Refractive index, n = Speed of light in vacuum, c/ Speed of light in the material, v  

Different mediums

Lighter medium to Denser medium speed decreases i > r 

Denser medium to lighter medium speed increases i < r 

Total Internal Reflection 

(a) Less than the critical angle and most light passes out 

(b) Equal to the critical angle and is reflected along the surface

(c) Greater than the critical angle and no light comes out; Total Internal Reflection

Sin C = 1/n (refractive index) 

Refraction by a prism

When light is refracted by a prism, it comes out in a different direction ---> deviated

If a narrow beam of white light is passed through a prism, it will split into a range of colours called a spectrum. The effect is called dispersion. It happens because a white light is not a single colour of the rainbow. The prism refracts each colour by a different amount. 

Optical fibres 

• very thin, flexible rods made of special glass or transparent plastic
• Light put in at one end is total internally reflected until it comes out of the other end
• Although some light is absorbed by the fibre it comes out of almost as bright as it came in 
•    

Paper Two- Analogue and Digital Signals 

+-----------+--------------+---------------+----------------------+--------------------------------+
| Type      | Examples     | Values        | Pros and Cons        | Additional Info.               |
+-----------+--------------+---------------+----------------------+--------------------------------+
| Analogue  | Sound        | Continuous    | Cons:                | takes values within a certain  |
|           | Light        | range         | Time consuming       | range                          |
|           | Temperature  |               | Lose quality         |                                |
|           |              |               | Picks up loads of    |                                |
|           |              |               | noise                |                                |
+-----------+--------------+---------------+----------------------+--------------------------------+
| Digital   | Sound        | Discontinuous | Pros:                | only takes two values on/off   |
|           | Morse code   | range         | Don't lose quality   | or 1/0                         |
|           |              |               | because they can be  |                                |
|           |              |               | regenerated          |                                |
|           |              |               | More information     |                                |
|           |              |               | Gets signals faster  |                                |
+-----------+--------------+---------------+----------------------+--------------------------------+

Digital signals can be regenerated meaning that there no loss in the signal quality, in contrast when an analogue signal becomes attenuated (loss of signal strength) it can only be amplified, but some of the signal quality is lost.  

Sound Waves

Sound waves will be reflected by hard flat surfaces. Things like carpets and curtains act as absorbing surfaces which will absorb sound, rather than reflect them.
They can also be refracted as they enter a different medium: as they enter denser material, they speed up.

Sound waves can also be diffracted through gaps and around obstacles

Longitudinal waves caused by vibrations
Human ear is capable of hearing sounds with frequencies between 20 Hz and 20000 Hz

Experiment to measure the speed of sound in air-
Measure the distance between two places, have a sound made in one place, as soon as you see the sound has been made start a stop watch, as soon as you hear the sound made stop the stopwatch.

Speed = Distance/ Time 

Paper Two- 
Oscilloscope:
Displays sound waves 
A sound wave receiver such as a microphone can pick up sound waves travelling through the air. To display these sound waves you connect the microphone to the oscilloscope and the microphone then converts the sound waves to electrical signals
Appearance of the wave tells us how loud or quiet and slow or fast and high- or low-pitched the sound is.  

The more something vibrates the higher frequency.
The higher frequency the higher pitch.
So the more vibrations the higher pitch.

Loudness increases with amplitude:
The greater the amplitude of a wave or vibration, the more energy it carries. In sound this means it is louder . Louder waves will also have a trace with a larger amplitude on the oscilloscope.