1. Critical angle is the angle of incidence where the angle of refraction is 90˚.

 2. a. If the angle of incidence is bigger than the critical angle, the wave will reflect.

     b. If the critical angle is bigger than the angle of incidence, the wave will refract .

     c. If the angle of incidence is equal to the critical angle, the wave will refract at 90˚ to the normal.

Endoscope

 3. The endoscope is an instrument used by doctors to see inside the body without surgery. It consists

     of 2 bundles of optical fibres. One half transmits light to the part of the body being investigated

     and the other half transmits the reflected light back to form an image.

 4. Three advantages of using optical fibres instead of copper wires for communication over long

     distances are:

• The signal loss in optical fibres is much less than in copper wires.

• Optical fibres do not corrode unlike copper wires.

• The amplification in optical fires is less frequent than in copper wires.