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. 

3b) Properties of waves

Different types of waves:

Longitudinal waves- The vibrations are along the SAME DIRECTION as the wave transfers energy
                          Examples- sound, ultrasound, shock waves and slinky spring has compressions when pushed

Traverse waves- The vibrations are at 90 degrees to the DIRECTION ENERGY IS TRANSFERRED by the wave
               Examples- light, all other EM waves, waves on strings, ripples on water and slinky spring goes up and down

Wavelength (λ)- is the distance from one peak to another
Frequency (f) - is how many complete waves there are per second. Measured in hertz (Hz)
Amplitude- is the height of the wave (from rest to crest)
Speed (v) - how fast it goes
Period (T) - the time taken for a complete wave to pass a point

Wave transfers energy and information without transferring matter:

• All waves carry energy in the direction they travel e.g. microwaves 
• waves can also be used as signals to transfer information form one place to another e.g. radio waves through the air 

Wave Speed = Frequency x Wavelength 

v = f x λ

Frequency and time period

f = 1/time period

Paper Two- Diffraction:

Is the spreading out of the waves into the area behind a barrier. The effect is the most noticeable when the wavelength is about the same as the gap through which they are moving 

Waves going through a gap that is BIGGER than their wavelength. They DON'T diffract

Waves going through a gap that is SMALLER than their wavelength. They DO diffract

a) No Diffraction- gap is much wider than wavelength 

b) Diffraction only on the edges- gap is a little bit wider that wavelength

c) Maximum diffraction- gap is the same as the wavelength 

When waves encounter obstacles diffraction causes them to bend around the obstacle. The LONGER the wavelength, the MORE they diffract and bend around.