Why is total internal reflection used in optical fibres?
Answer and explanation
Correct answer: A. Light is reflected repeatedly inside the fibre when the angle exceeds the critical angle
- Step 1: If the angle of incidence is larger than the critical angle, all of the light is reflected.
- Step 2: So the light is trapped and carried along the fibre.
Answer
Light is reflected repeatedly inside the fibre when the angle exceeds the critical angle.
Why not the others: Light is absorbed by the glass and re-emitted: this would lose the signal. Light is refracted out of the fibre at each bend: then the signal would be lost. Light travels faster in glass than in air: light travels slower in glass.
Practise more Properties of Matter, Waves and Radiation.
Free questions with an explanation for every one, and full timed National 5 (Scotland) mock tests.
More Properties of Matter, Waves and Radiation questions
- A force of 600 N is applied to an area of 0.020 m². What is the pressure?
- Calculate the energy needed to raise the temperature of 2.0 kg of water by 10 °C (c = 4180 J/kg/°C).
- How much energy is needed to melt 0.50 kg of ice at 0 °C? (specific latent heat of fusion of ice = 3.34 × 10⁵ J/kg)
- A gas at a constant temperature has a volume of 4.0 litres at 100 kPa. It is compressed to 2.0 litres. What is the new pressure?
- A sealed container of gas at 300 K and 100 kPa is heated at constant volume to 360 K. What is the new pressure?
- What is 20 °C in kelvin?