 µ IB | Refraction (+reflection)

10 quick questions

10 minutes maximum! (can you do it in 5?)

1. The 'normal line' is an important concept in the topic of refraction. it is drawn at the point where the wave hits the refracting medium.

Which of these is the best description of a normal line?

• A. A line parallel to the surface of the refracting medium.
• B. A line perpendicular to the surface of the refracting medium.
• C. A horizontal line at the point of refraction of the wave.
• D. A vertical line at the point of refraction of the wave.

2. The angles of refraction should always be measured between ..

• A. ..the refracted wave and the incident wave.
• B. ..the refracted wave and the surface of the medium.
• C. ..the refracted wave and the normal line.
• D. ..the normal line and the surface of the medium.

3. A prism refracts light. Which of the following diagrams correctly shows the relevant normal lines and the light being refracted in the correct direction?
(Angles in the diagram are approximate). 4. A rope is tied to a pole and two wave pulses are produced by moving the end of the rope up and down. The first pulse produced is weak, the second is much stronger and has a higher amplitude as shown below: The pulses are reflected on impact with the pole. Which of the following diagrams shows the reflected pulses correctly? 5. Total internal reflection will only occur if a wave is incident on a surface such as glass under certain conditions. Which of these best describes these conditions?

• A. The angle or refraction is greater than the critical angle, and the ray is travelling in air towards the glass.
• B. .The angle or refraction is less than the critical angle, and the ray is travelling in air towards the glass.
• C. The angle or refraction is greater than the critical angle, and the ray is travelling in glass towards the air.
• D. The angle or refraction is less than the critical angle, and the ray is travelling in glass towards the air.

6. Which of these is the best description of the critical angle of a medium?

• A. The angle of the incident ray when the refracted ray is at 900 to the normal line.
• B. The angle of the incident ray when the refracted ray is parallel to the normal line.
• C. The angle of the refracted ray when the incident ray is at 900 to the normal line.
• D. The angle of the refracted ray when the incident ray is at parallel to the normal line.

7&8. Water will refract light but also refract sound.

The table below gives typical values for the speed of sound and light in sea water and in air.

 speed in air / ms-1 speed in sea water / ms-1 sound 340 1500 light 3.0 x 10 8 2.3 x 10 8

(Speeds given to 2 sig figs).

Light and sound waves pass from air into water at an angle of incidence = 10o. Which of the answers in the table below gives the refracted angles for sound and light?

 Angle of refraction of sound. Angle of refraction of light. A > 10o > 10o B < 10o > 10o C > 10o < 100 D < 10o < 10o

8. If the refractive indes of air is equal to 1.0, what is the refractive index of sea water for a light wave? Q9&10. A light ray is incident on a glass block as shown.

The refractive index of the air is 1.0, and 1.6 for the glass.

Tthe value of sin ( 300 ) is 0.5 . 9. As the light ray enters the glass and changes direction, some properties of the wave change. Which of these best describes the changes to the wave properties?

 speed of wave frequency Wavelength A decreases decreases stays constant B increases stays constant decreases C increases decreases stays constant D decreases stays constant decreases

10. Which of these formulas is equal to the angle of incidence, i? 