9TH GRADE · LIGHT PHENOMENA
Light propagation and reflection
Sources, shadow, eclipses, mirror and the law of reflection.
The entire theory of the lesson is collected here; you can read it without an account. In interactive mode, the same theory appears as cards, followed by questions. with checking the answer and task, and progress is saved.
Basic Concepts
Law of Reflection
The incident ray, reflected ray and normal lie in the same plane, and the angles of incidence and reflection are equal.
Angles are measured from the normal to the surface, and not from the surface itself.
Image in a plane mirror
A plane mirror produces a virtual direct image of equal size at the same distance behind the mirror.
The construction is carried out by continuation of the reflected rays, which visually converge behind the mirror.
Rectilinear propagation of light
In a homogeneous transparent medium, light propagates in a straight line, which allows the use of the ray model.
Shadow, penumbra, solar and lunar eclipses are explained by the geometry of the rays and the finite dimensions of the source.
Physical quantities
Angle of incidence
The angle between the incident ray and the normal to the surface.
Unit: radian ·
Reflection angle
The angle between the reflected ray and the normal to the surface.
Unit: radian ·
Lesson formulas
Law of Reflection
The angle of incidence is equal to the angle of reflection if both are measured from the normal.
Tasks on the topic
Statements, answer options and the walkthrough.