Reflection and refraction of lightIB MYP Sciences: Subtopic test

1. 1
   A dentist uses a small plane (flat) mirror on a handle to look at the back of a patient's teeth. Light from a lamp reflects from the tooth, then from the mirror, and into her eye.

   (a)

   A ray of light hits the mirror with an angle of incidence of 30°. What is the angle of reflection?

   [1 mark]

   • A60°
   • B15°
   • C30°
   • D0°

   (b)

   Which statement describes the image of a tooth seen in a plane mirror?

   [1 mark]

   • AReal, upside down and smaller than the tooth
   • BReal, upright and the same distance in front of the mirror
   • CVirtual, upright and magnified, behind the mirror
   • DVirtual, upright and the same size, as far behind the mirror as the tooth is in front

   (c)

   State the law of reflection and the line from which the angles are measured.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student in a school laboratory shines a narrow ray of light from a ray box onto a rectangular glass block. The ray bends where it enters the glass and bends again where it leaves the glass on the other side.

   (a)

   What happens to the ray as it enters the glass block at an angle?

   [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 keeps the same speed and bends away from the normal

   (b)

   What happens to the ray as it leaves the glass block into the air at an angle?

   [1 mark]

   • AIt slows down and bends towards the normal
   • BIt speeds up and bends away from the normal
   • CIt speeds up and bends towards the normal
   • DIt keeps the same speed and travels straight on

   (c)

   A second ray hits the glass block along the normal, at 0° to it. Describe what happens to the ray and explain why.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Students in Kuala Lumpur investigate how light bends as it enters a rectangular glass block. They shine a thin ray at the block at three different angles of incidence, and measure the angle of refraction with a protractor each time. For angles of incidence of 20°, 40° and 60° the angles of refraction are 13°, 25° and 35°. Each angle was measured once.

   (a)

   State a testable hypothesis for this investigation, and identify the independent variable and the dependent variable.

   [3 marks]

   (b)

   Describe the trend in the results and explain why the angle of refraction is smaller than the angle of incidence. Suggest one improvement to make the results more reliable.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Surgeons use endoscopes containing optical fibres, which are thin strands of glass, to look inside the body through very small cuts. Light travels along each fibre by total internal reflection. Companies also lay fibre-optic cables across the sea bed to carry internet signals. Endoscopes are expensive and must be sterilised, undersea cables are costly to lay and can disturb the sea bed, and glass fibres can snap if bent too sharply.

   (a)

   Explain how light is able to travel along an optical fibre, even when the fibre is bent.

   [6 marks]

   (b)

   Discuss the benefits and drawbacks of using optical fibres in medicine and in communications, and evaluate whether their use is justified.

   [6 marks]

   Total for question 4: 12 marks

End of questions