Total internal reflection. n1sin1= n2sin2 If θ2=90 sin2=1  θ1= θc  n1sinc= n2 Critical Angle

Light Box activity

http://www.ngsir.netfirms.com/englishhtm/RefractionByPrism.htm

Diamond has a high refractive index Diamond has a high refractive index. With clever cutting a diamond sparkles as the light that enters is internally reflected back out the front.

Binoculars The triangular prisms totally internally reflect the light so the binoculars can be made shorter than telescopes

Fibre Optics Fibre optic cables are constructed of glass fibres that carry pulses of light.

The glass fibre has a second glass cladding of a lower n (and then a plastic covering) This allows the light to totally internally reflect down the fibre.

(Left ) Strands of glass optical fibers are used to carry voice, video, and data signals in telecommunication networks. p.1114

Figure 35. 30 The construction of an optical fiber Figure 35.30 The construction of an optical fiber. Light travels in the core, which is surrounded by a cladding and a protective jacket. Fig 35-30, p.1114

Figure 35.29 Light travels in a curved transparent rod by multiple internal reflections. Fig 35-29, p.1114

Optical fiber communication system Electrical/optical converter Decoder Electric signal Fiber Optical/electrical converter Encoder Repeater Digital encoding scheme for optical communications “One” “Zero” High-power pulse  “one” Low-power pulse  “zero” High-power pulse  “One”

Fibre optics have many advantages over copper which include: 1. Smaller 3. Clearer signal 2. More than one call per fibre (1000 calls at once) 4. Difficult to intercept information (bug) http://acept.asu.edu/PiN/mod/light/opticsnature/pattLight4.html 5. Greater band width

No light is absorbed at each reflection so that, as long as the glass is clear, then the pulses can travel many km’s through the fibre. Uses of fibre optics include:

1. Medicine a) to view An endoscope can be inserted into the body with minimal surgery (non-invasive).

Once in the body it can diagnose and/or treat a condition.

b) to deliver laser light

One fibre can collect light from each source (star, galaxy etc) One fibre can collect light from each source (star, galaxy etc). This light can then be analysed and information about size, distance composition etc can be found. 2. Telescopes

3. Communications Most use of fibre optics is in communications. Information can be carried as electrical signals down copper wires.