Test yourself markscheme - Refraction, refractive index and total internal reflection

Mark scheme for exam questions - How did you do???

(a)   (i)    Critical angle

       (ii)   The light is totally internally reflected. 

       It would be insufficient to simply say that ‘the light is reflected’ or even 

      ‘reflected back into the block’.

       (iii)   refractive index =  1/ sin c 

                                        = 1/ sin 42

                                        = 1/ 0.669 = 1.5

       Alternatively the equation refractive index = sin i/sin r could have been used.      

       However, if you use this equation you must imagine the light to be travelling from

       air into glass and not the other way around. So take the angle of incidence as 

       either 31° or 49° with the associated angle of refraction either 20° or 30°.

(b)

• An endoscope has two bundles of optical fibres. 
• Light that is directed into one bundle travels from one end to the other by being totally internally reflected many times. 
• The light is then reflected back through the second bundle of optical fibres.
• The image is viewed through a lens, 
• or if a miniature camera is attached to the optical fibres the image can be displayed on a computer screen.

    It is perfectly okay to answer a ‘prose’ type question using bullet points. However, if 

    you do, make sure each bullet point is a complete sentence.

Total Internal Reflection

Yet another good video from My GCSE Science

http://www.my-gcsescience.com/revision/separate/total-internal-reflection

Contains information about calculating the refractive index using the sine of the critical angle, describing how optical fibres work and describing the use of lasers.

Specification reference P3.1.5 Other applications of light
You should know that:

• refractive index = 1 / sin c, where c is the critical angle
• visible light can be sent along optical fibres - examples of use should include the endoscope for internal imaging.
• a laser can be used as an energy source for cutting, cauterising and burning (knowledge of how lasers work is not required. Applications should include use in eye surgery)