Practice Questions: Geometric Optics
Subject: Physics | Grade: 11 | Topic: Geometric Optic
Practice Questions: Geometric Optics
Give one word for each of the following descriptions:
- The perpendicular line drawn at right angles to a reflecting surface at the point of incidence.
- The bending of light as it travels from one medium to another.
- The bouncing of light off a surface.
1.1 Normal
1.2 Refraction
1.3 Reflection
State whether the following statements are true or false. If false, rewrite the statement correctly.
- The refractive index of a medium is an indication of how fast light will travel through the medium.
- Total internal reflection takes place when the incident angle is larger than the critical angle.
- The speed of light in a vacuum is about \(3 \times 10^8\,\text{m}\cdot\text{s}^{-1}\).
2.1 True. A higher refractive index means light travels more slowly in that medium.
2.2 True, but only when light travels from a more optically dense medium to a less optically dense medium.
2.3 True.
Complete the ray diagram for light travelling from glass to water. The critical angle for glass to water is approximately \(62.5^\circ\). In this example, the incident angle is \(40^\circ\).
Since \(40^\circ\) is less than the critical angle, the light refracts into the water. It bends away from the normal because it travels from glass \((n = 1.50)\) to water \((n = 1.33)\).
Give one word for each description.
- The line drawn perpendicular to a surface at the point where a ray strikes the surface.
- The change in direction of light when it enters a different medium.
- The bouncing back of light from a surface.
1.1 Normal
1.2 Refraction
1.3 Reflection
State whether each statement is true or false. If false, rewrite it correctly.
- The refractive index of a medium gives information about the speed of light in that medium.
- Total internal reflection can happen at any boundary if the incident angle is large enough.
- The speed of light in a vacuum is approximately \(3 \times 10^8\,\text{m}\cdot\text{s}^{-1}\).
2.1 True.
2.2 False. Total internal reflection only occurs when light travels from a more optically dense medium to a less optically dense medium and the incident angle is greater than the critical angle.
2.3 True.
Complete the following ray diagrams for light travelling from glass to water. Use \(\theta_c \approx 62.5^\circ\) for the glass-water boundary.
A) \(40^\circ\)
B) \(30^\circ\)
C) \(42^\circ\)
D) \(50^\circ\)
E) \(48.8^\circ\)
F) \(55^\circ\)
All given angles are less than \(62.5^\circ\), so each ray refracts into the water and bends away from the normal. None of these examples produces total internal reflection for a glass-water boundary.
Note: \(48.8^\circ\) is the critical angle for water-air, not glass-water. For glass-water, the critical angle is about \(62.5^\circ\).
A ray of light strikes a surface at \(35^\circ\) to the normal. Draw a ray diagram showing the incident ray, reflected ray and surface normal. Calculate the angles of incidence and reflection.
The angle of incidence is \(35^\circ\).
According to the law of reflection:
\(\theta_i = \theta_r\)
The angle of reflection is also \(35^\circ\).
Light travels from glass \((n = 1.5)\) to acetone \((n = 1.36)\). The angle of incidence is \(25^\circ\).
16.1 Describe the path of light as it moves into the acetone.
16.2 Calculate the angle of refraction.
16.3 What happens to the speed of the light as it moves from the glass to the acetone?
16.4 What happens to the wavelength of the light as it moves into the acetone?
Light strikes the interface between diamond and an unknown medium with an incident angle of \(32^\circ\). The angle of refraction is measured to be \(46^\circ\). Calculate the refractive index of the medium and identify the medium.
Explain what total internal reflection is and how it is used in medicine and telecommunications. Why is this technology useful?