1. 1
   A shop-window designer positions a flat mirror at the back of a display case so that customers standing outside the shop can see reflected light from a spotlight aimed at the mirror. A ray of light from the spotlight strikes the flat mirror at an angle of incidence of 35 degrees, measured from the normal.

   (a)

   A ray of light strikes the mirror at an angle of incidence of 35 degrees. What is the angle of reflection?

   [1 mark]

   • A35 degrees
   • B55 degrees
   • C70 degrees
   • D17.5 degrees

   (b)

   The angle of incidence is measured from which reference line on the mirror's surface?

   [1 mark]

   • AThe mirror's surface itself
   • BThe normal, an imaginary line perpendicular to the mirror's surface at the point of incidence
   • CA line parallel to the incident ray
   • DThe horizon, an imaginary horizontal line

   (c)

   The designer tilts the mirror slightly so that the angle of incidence increases to 50 degrees. Describe what happens to the angle of reflection, and explain why the reflected ray changes direction.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A jeweller is investigating a rectangular glass block used to make display cases. A ray of light strikes the flat surface of the glass block from air at an angle of incidence of 48.6 degrees and is refracted to an angle of refraction of 30 degrees inside the glass.

   (a)

   As the ray of light passes from the air into the glass block, calculate the refractive index of the glass.

   [1 mark]

   • A30
   • B0.67
   • C2.25
   • D1.50

   (b)

   Why does the ray of light bend towards the normal as it enters the glass block from the air?

   [1 mark]

   • ABecause the glass block absorbs some of the light's energy
   • BBecause light travels faster in the denser glass than in air
   • CBecause light travels more slowly in the denser glass than in air
   • DBecause the frequency of the light changes as it enters the glass

   (c)

   Calculate the critical angle for light travelling from this type of glass back into air.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A telecommunications engineer is explaining how an optical fibre carries information as pulses of light along its length. The fibre consists of a glass core surrounded by a second material with a lower refractive index.

   (a)

   Explain, using the idea of the critical angle, how total internal reflection occurs at the boundary between the glass core of an optical fibre and the material surrounding it.

   [3 marks]

   (b)

   Describe an investigation using a semi-circular glass block that could be used to determine the critical angle of the glass experimentally, including how the point at which total internal reflection begins would be identified.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A team of engineers is designing a new endoscope, a medical instrument that uses a bundle of optical fibres to carry light into the body and transmit an image back to a doctor.

   (a)

   Explain, referring to reflection, refraction and total internal reflection, how light behaves as it travels along an individual optical fibre within the endoscope, and why this makes optical fibres suitable for this medical use.

   [6 marks]

   (b)

   Evaluate why a bundle of optical fibres, rather than a single wide glass rod, is used to carry the image in the endoscope, referring to how the arrangement of many thin fibres affects the reliability of total internal reflection as the endoscope bends around corners inside the body.

   [6 marks]

   Total for question 4: 12 marks

End of questions