IB MYP 4-5 Physics- Reflection of light- Study Notes - New Syllabus
IB MYP 4-5 Physics-Reflection of light- Study Notes
Key Concepts
- Reflection of light
Reflection of Light
Reflection of Light
Reflection is the bouncing back of light rays when they strike a smooth or polished surface, such as a mirror.
Laws of Reflection:
- The incident ray, the reflected ray, and the normal (a line perpendicular to the surface) all lie in the same plane.
- The angle of incidence (\( \theta_i \)) is equal to the angle of reflection (\( \theta_r \)).
\( \theta_i = \theta_r \)
Types of Reflection:
- Regular Reflection: Occurs on a smooth surface (like a mirror). The reflected rays are parallel, producing clear images.
- Diffuse Reflection: Occurs on a rough surface (like paper). The reflected rays scatter in different directions, and no clear image is formed.
Applications:
- Periscopes use mirrors for reflection of light.
- Rear-view mirrors in vehicles provide visibility.
- Reflectors on bicycles use reflection to make them visible in the dark.
Example:
A light ray strikes a plane mirror at an angle of incidence \(30^\circ\). Find the angle of reflection.
▶️ Answer/Explanation
By the law of reflection: \( \theta_r = \theta_i = 30^\circ \). So, the angle of reflection is \( \boxed{30^\circ} \).
Example:
Why do you see your reflection clearly in a mirror but not on a piece of white paper?
▶️ Answer/Explanation
A mirror has a smooth surface, so it produces regular reflection, with reflected rays parallel and forming a clear image. Paper has a rough surface, causing diffuse reflection, where light rays scatter in many directions, so no clear image is formed.
Example:
A periscope uses two plane mirrors placed at \(45^\circ\). How does reflection help someone see over a wall?
▶️ Answer/Explanation
Light from the object strikes the first mirror and reflects downwards at the same angle. It then strikes the second mirror, which reflects it horizontally into the observer’s eye. Thus, reflection allows light to change direction twice, letting the observer see over obstacles.