IB MYP 4-5 Physics- Refraction of light- Study Notes - New Syllabus
IB MYP 4-5 Physics-Refraction of light- Study Notes
Key Concepts
- Refraction of light
Refraction of Light
Refraction of Light
Refraction is the bending of light when it passes from one transparent medium into another, caused by a change in speed of light.
- Light bends towards the normal when it passes from a rarer medium (like air) to a denser medium (like glass or water).
- Light bends away from the normal when it passes from a denser medium to a rarer medium.
- If the ray enters perpendicular (along the normal), it does not bend, only changes speed.
Laws of Refraction:
- The incident ray, refracted ray, and the normal at the point of incidence all lie in the same plane.
- The ratio of the sine of the angle of incidence (\( \theta_i \)) to the sine of the angle of refraction (\( \theta_r \)) is constant for the same two media.
This constant is the refractive index (\(n\)): \( n = \dfrac{\sin \theta_i}{\sin \theta_r} \)
Refractive Index (\(n\)):
- It is a measure of how much the medium slows down light.
- Formula in terms of speed:
\( n = \dfrac{c}{v} \)
where \(c\) = speed of light in vacuum, \(v\) = speed of light in the medium.
Applications of Refraction:
- Lenses in glasses, microscopes, and cameras.
- Mirage formation due to air layers of varying density.
- A straw in water appearing bent at the surface.
Example:
A light ray enters glass from air at an angle of incidence \(45^\circ\). The angle of refraction is \(28^\circ\). Find the refractive index of glass.
▶️ Answer/Explanation
Using Snell’s law: \( n = \dfrac{\sin \theta_i}{\sin \theta_r} \) \( n = \dfrac{\sin 45^\circ}{\sin 28^\circ} \) \( n = \dfrac{0.707}{0.469} \approx 1.51 \).
Thus, the refractive index of glass is \( \boxed{1.51} \).
Example:
A coin is placed at the bottom of a glass container filled with water. The real depth is 12 cm, and the refractive index of water is 1.33. What is the apparent depth?
▶️ Answer/Explanation
Formula: Apparent depth = \( \dfrac{\text{Real depth}}{n} \) = \( \dfrac{12}{1.33} \approx 9.0 \, \text{cm} \).
So, the coin appears at \( \boxed{9.0 \, \text{cm}} \).
Example:
Why does a road look wet on a hot sunny day?
▶️ Answer/Explanation
On hot days, the air near the ground is less dense than the air above. Light from the sky bends gradually due to refraction in layers of different density air. The observer sees a virtual image of the sky on the road surface, making it look like water. This is called a mirage.