Chapter focus
Trace light paths and compare how mirrors reflect light and lenses refract it. Use ray diagrams to make image descriptions.
These are original study notes and practice questions prepared for revision. Use your assigned NCERT edition for the complete lesson, diagrams, activities, and exercise wording.
What you will learn
- Explain the main idea: Trace light paths and compare how mirrors reflect light and lenses refract it. Use ray diagrams to make image descriptions.
- Use the key terms and relationships in the notes below.
- Show your reasoning and check whether an answer fits the question.
Key ideas and notes
- Light travels in straight lines through a uniform transparent medium.
- A plane mirror forms an upright virtual image the same distance behind the mirror as the object is in front.
- A convex lens can converge parallel rays; a concave lens diverges them.
Worked example
If an object is 2 m in front of a plane mirror, its image appears 2 m behind it.
Quick revision
Light travels in straight lines through a uniform transparent medium.
A plane mirror forms an upright virtual image the same distance behind the mirror as the object is in front.
A convex lens can converge parallel rays; a concave lens diverges them.
Original practice questions
Try each question first. Open the answer to check your reasoning.
State the law of reflection for angles.
Answer: Angle of incidence equals angle of reflection, measured from the normal.
Which lens is thicker at the centre: convex or concave?
Answer: Convex.
Why can a lens change the direction of a light ray?
Answer: Refraction occurs as light changes speed between materials.
Chapter summary
Trace light paths and compare how mirrors reflect light and lenses refract it. Use ray diagrams to make image descriptions. The key ideas above give you a short revision path; practise explaining them in your own words and revisit any step you could not justify.