1. 1
   A telecommunications company transmits data as pulses of light along a thin glass optical fibre, relying on the light continually reflecting internally along the length of the fibre without escaping through its sides.

   (a)

   What happens to the direction of a light wave when it is reflected at a boundary?

   [1 mark]

   • Athe angle of incidence equals the angle of reflection
   • Bthe angle of incidence is always greater than the angle of reflection
   • Cthe light wave stops travelling
   • Dthe light wave changes speed but not direction

   (b)

   For total internal reflection to occur at the boundary inside the optical fibre, the angle of incidence inside the fibre must be:

   [1 mark]

   • Aless than the critical angle
   • Bgreater than the critical angle
   • Cexactly 0°
   • Dequal to the angle of refraction

   (c)

   State the two conditions required for total internal reflection to occur when light travelling inside an optical fibre reaches the boundary with the outer coating.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student places a drinking straw in a glass of water and observes that the straw appears to bend at the surface where it enters the water.

   (a)

   Why does the straw appear to bend at the water's surface?

   [1 mark]

   • Athe light reflects off the surface only
   • Bthe eye cannot see through water
   • Cthe straw physically bends when placed in water
   • Dlight refracts (changes direction) as it passes from water into air

   (b)

   As light travels from water (denser medium) into air (less dense medium), what happens to its speed?

   [1 mark]

   • Ait decreases
   • Bit stays the same
   • Cit increases
   • Dit becomes zero

   (c)

   Light travelling through the water in the glass has a wavelength of 450 nm and a frequency of 5.0 × 10^14 Hz. Calculate the speed of light in the water.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Road engineers install reflective 'cat's eye' studs along the centre of country roads at night, which use small glass or plastic prisms designed so that light from car headlights undergoes total internal reflection and is sent back towards the driver, without needing a power supply.

   (a)

   Explain, using the idea of total internal reflection, how a cat's eye road stud reflects a car's headlight beam back towards the driver, rather than the light simply passing through or scattering in all directions.

   [3 marks]

   (b)

   Explain why cat's eye studs are more useful for road safety at night than a flat piece of ordinary window glass would be, and suggest one advantage of using total internal reflection rather than a coated (silvered) mirror surface inside the stud.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Submarine engineers in the 20th century developed periscopes using angled mirrors to redirect light for observation above the waterline, a design principle later adapted by medical engineers into flexible fibre-optic endoscopes that use total internal reflection along bundles of glass fibres to let doctors see inside a patient's body.

   (a)

   Compare how a submarine periscope uses reflection from flat mirrors with how a modern medical endoscope uses total internal reflection along an optical fibre to redirect light, explaining the physics principle used in each case.

   [6 marks]

   (b)

   Evaluate why total internal reflection along a flexible optical fibre is more suitable than rigid mirrors for guiding light deep inside a patient's body during an endoscopy, considering the practical constraints of moving instruments through the body's natural passages.

   [6 marks]

   Total for question 4: 12 marks

End of questions