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๐ฌ Think about it
Hold a concave mirror close and you look big; step back and you flip upside down. A convex mirror always shrinks you, no matter what. The image depends on the mirror and how far you stand. Let's pin down these patterns.
What image does a concave mirror form?
- When the object is close, the image is erect and enlarged.
- As the object moves away, the image becomes inverted.
- The inverted image then keeps getting smaller.
- So the image depends on the object's distance.
Example:
Your face looks big in a concave mirror held close, but flips upside down when you step back.
What image does a convex mirror form?
- A convex mirror always forms an erect image.
- The image is always smaller than the object (diminished).
- The image shrinks a little more as the object moves away.
- It never becomes inverted.
Example:
A vehicle's side-view mirror always shows traffic upright but smaller.
In this Activity, we will compare the images formed by concave and convex mirrors at different distances.
Materials needed
A concave mirror, a convex mirror, two small blocks to hold them upright, a small toy or object.
Procedure
1. Place both mirrors upright, side by side, on a table.
2. Keep the object in front of them at a small distance (3–4 cm).
3. Note the size, whether erect, and any lateral inversion.
4. Slowly move the object away and note the changes.
5. Repeat with each mirror individually and draw conclusions.
2. Keep the object in front of them at a small distance (3–4 cm).
3. Note the size, whether erect, and any lateral inversion.
4. Slowly move the object away and note the changes.
5. Repeat with each mirror individually and draw conclusions.
Observation
The concave image is enlarged and erect up close, then inverted and smaller when far. The convex image is always erect and diminished.
Explanation
Spherical mirrors behave differently from plane mirrors. The image size changes with distance, and the concave mirror also inverts the image when the object is far. Lateral inversion is seen in all three mirror types.
โ Summary
- Object placed near
- Then moved far
- Images compared
- Conclusions drawn
Where are concave mirrors used?
- Reflectors of torches and vehicle headlights are concave.
- They gather light into a strong beam.
- A dentist's mirror is concave.
- It gives an enlarged view of teeth when held close.
Example:
A torch reflector is concave, throwing a bright focused beam ahead.
๐ก A step further
- Most modern telescopes are reflecting telescopes.
- They use curved mirrors to gather light.
- The main mirror is a large concave mirror.
- This helps astronomers see distant stars and planets.
Where are convex mirrors used?
- Vehicle side-view mirrors are convex.
- They show a wider area of the road behind.
- They are placed at sharp bends to prevent collisions.
- Big stores use them to watch a large area.
Example:
A scooter's side-view mirror is convex, giving a wide view of traffic behind.
Important Points
- Concave mirror: enlarged erect when near, inverted smaller when far.
- Convex mirror: always erect and diminished.
- Concave mirrors focus light; convex mirrors widen the view.
โ Test Yourself
-
What image does a convex mirror always form?
View Answer
An erect and diminished (smaller) image, no matter where the object is placed. -
When does a concave mirror form an inverted image?
View Answer
When the object is moved far from the mirror. Up close, the image is erect and enlarged. -
Why are convex mirrors used as side-view mirrors?
View Answer
They give an erect, smaller image and show a much wider area of the road behind. -
Why is a dentist's mirror concave?
View Answer
Held close to the teeth, a concave mirror gives an enlarged view, helping the dentist inspect them. -
Is lateral inversion seen in spherical mirrors?
View Answer
Yes. Lateral inversion is seen in all three mirror types — plane, concave, and convex.
Important Definitions
- Enlarged image — an image larger than the object.
- Diminished image — an image smaller than the object.
- Erect image — an image that is the same way up as the object.
- Inverted image — an image that is upside down compared with the object.
๐ NCERT Question 3 — In Fig. 10.23, the
Match each image of a sketch-pen cap with the correct mirror (plane, convex, concave).
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๐ NCERT Question 7 — In a museum, a
A woman walks towards a large concave mirror. What does she see happen to her image?
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๐ NCERT Question 10 — The following question is
Assertion-Reason: convex mirrors are preferred for observing traffic behind us.
View Answer →
๐ NCERT Question 11 — In Fig. 10.27, note
Using object, mirror, and image positions, identify which figure shows which mirror.
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