Reflection and refractionIB MYP Physics: Subtopic test

1. 1
   A student in Lagos investigates reflection using a ray box and a plane mirror laid flat on a sheet of paper. She draws a line at right angles to the mirror at the point where a ray of light hits it. The ray hits the mirror at 30° to the surface of the mirror. She then places a pencil in front of the mirror and looks at its image.

   (a)

   What is the angle of reflection of the ray?

   [1 mark]

   • A30°
   • B90°
   • C120°
   • D60°

   (b)

   What is the normal?

   [1 mark]

   • AA line drawn along the surface of the mirror
   • BA line drawn at 90° to the mirror at the point where the ray hits it
   • CThe path of the reflected ray
   • DA line joining the object to its image

   (c)

   Describe two properties of the image of the pencil seen in the plane mirror.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In a physics laboratory in Seoul, a ray of light passes from air into a rectangular glass block. The angle of incidence is 50° and the angle of refraction is 30°.

   (a)

   What happens to the light as it enters the glass?

   [1 mark]

   • AIt slows down and bends towards the normal
   • BIt speeds up and bends towards the normal
   • CIt slows down and bends away from the normal
   • DIt speeds up and bends away from the normal

   (b)

   What is the refractive index of the glass?

   [1 mark]

   • A0.65
   • B1.67
   • C1.53
   • D0.77

   (c)

   The student then shines a ray of light into the glass block along the normal. State what happens to the direction and the speed of the ray as it enters the glass.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student investigates refraction using a rectangular glass block, a ray box and a protractor. She shines a ray of light into the block from air at different angles of incidence and measures the angle of refraction each time. For angles of incidence of 20°, 40° and 60°, she measures angles of refraction of 13°, 25° and 35°.

   (a)

   Use the readings for an angle of incidence of 60° to calculate the refractive index of the glass.

   [3 marks]

   (b)

   Describe the trend in the results and suggest two ways in which the student could improve the accuracy of the investigation.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A telecommunications company in Nairobi is replacing copper cables with optical fibres to carry internet signals as pulses of light. Each fibre is a very thin strand of glass. The light is guided along the fibre by total internal reflection. The critical angle for the glass–air boundary is 42°.

   (a)

   Explain how total internal reflection happens and how it keeps the light inside the fibre.

   [6 marks]

   (b)

   Discuss the benefits and drawbacks of replacing copper cables with optical fibres, and evaluate whether the company should do so.

   [6 marks]

   Total for question 4: 12 marks

End of questions