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CISCE(English Medium) ICSE Class 9
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पाठ्यक्रम

Image Formation by Concave Mirror

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Topics

  • Experiment
  • Image Formation by Concave Mirror

Experiment

1. Aim: To study the images formed by a concave mirror for different object distances.

2. Requirements: concave mirror, candle or lamp, cardboard box with an arrow-shaped slit, screen (white paper on cardboard), meter scale, wooden block.

3. Procedure

  • Set up the cardboard box with the arrow-shaped slit as a light source.
  • Place the mirror vertically in a cardboard box and align it with the meter scale at the 0 mark.
  • In a dark room, position the light source between the mirror and the screen. Ensure the distance between the source and mirror is slightly more than the focal length.
  • Move the screen along the meter scale until a clear image of the source is formed. Observe the image: it is inverted, real, and larger than the source.
  • Move the light source further away from the mirror to a distance greater than twice the focal length. Adjust the screen to get a clear image. This time, the image is inverted, real, and smaller than the source.
  • Measure the distances for each case using the meter scale.

Images formed by a plane mirror

4. Conclusion: The experiment demonstrates how a concave mirror forms real and inverted images of varying sizes, depending on the object's distance relative to the mirror's focal length.

Image Formation by Concave Mirror:

In Figure A, an object AB is placed between the focus and the centre of curvature C of a concave mirror MN.

  • The incident ray AQ, starting from the top of the object , passes through the focus . After reflection, it becomes parallel to the principal axis and travels along QR.
  • Another incident ray AS, parallel to the principal axis, reflects through the focus and travels along ST. The reflected rays QR and ST intersect at point A1, forming the image of at A1. Since lies on the principal axis, its image is directly above A1, at B1.
  • The images of points between and lie between A1 and B1. Thus, the image of the object AB is A1B1. When the object is placed between the focus and centre of curvature C, the image forms beyond the centre of curvature.
  • The image is real, inverted, and larger than the object, as the reflected rays actually intersect. This image can be obtained on a screen.

In Figure 2B, the object AB is placed between the pole and the focus of the mirror.

  • The incident ray AQ, parallel to the principal axis, reflects through the focus . Another incident ray AS is directed toward the centre of curvature . After reflection, it retraces its path back.
  • The reflected rays do not actually meet but appear to meet behind the mirror at A1 and B1.
  • The image formed is virtual, erect, and larger than the object, as the reflected rays appear to converge behind the mirror. This virtual image cannot be obtained on a screen and is located behind the mirror.

Images obtained in a concave mirror

No. Position of the Object Position of the Image Nature of Image Size of the Image
1 Between pole and focus Behind the mirror Erect, virtual Magnified
2 At the focus At infinity Inverted, real Very large
3 Between focus and centre of curvature Beyond the centre of curvature Inverted, real Magnified
4 At the centre of curvature At the centre of curvature Inverted, real Same as the object
5 Beyond the centre of curvature Between the centre of curvature and focus Inverted, real Diminished
6 At a very large (infinite) distance At focus Inverted, real Point image

 

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Related QuestionsVIEW ALL [9]

Draw ray diagrams for the cases of images obtained in concave mirrors as described in the table below. 

Images formed by concave mirrors
No. Position of the object Position of the image Nature of image Size of the image
1 Between pole and focus  Behind the mirror  Erect, virtual Magnified
2 At the focus  At infinity  Inverted, real  Very large
3 Between focus and centre of curvature Beyond the centre of curvature Inverted, real Magnified
4 At the centre of 
curvature 		 At the centre of curvature Inverted, real  Same as the object
5 Object between infinity and Centre of curvature Between the centre of curvature and focus Inverted, real  Diminished
6 Object at infinity At focus Inverted, real  Diminished

A 10 cm long pencil is placed 5 cm in front of a concave mirror having a radius of curvature of 40 cm.

  1. Determine the position of the image formed by this mirror.
  2. What is the size of the image?
  3. Draw a ray diagram to show the formation of the image as mentioned in part (i).

Draw ray diagrams showing the image formation by a concave mirror when an object is placed

  1.  between pole and focus of the mirror
  2. between focus and centre of curvature of the mirror
  3. at centre of curvature of the mirror
  4. a little beyond centre of curvature of the mirror
  5. at infinity

Assertion: For observing the traffic at a hairpin bend in mountain paths a plane mirror is preferred over convex mirror and concave mirror.

Reason: A convex mirror has a much larger field of view than a plane mirror or a concave mirror.

Rohit wants to have an erect image of an object using a converging mirror of focal length 40 cm.

  1. Specify the range of distance where the object can be placed in front of the mirror. Justify.
  2. Draw a ray diagram to show image formation in this case.
  3. State one use of the mirror based on the above kind of image formation.

If an object is placed at the focus of a concave mirror, where is the image formed?

  1. Complete the diagram to show how a concave mirror forms the image of the object.
  2. What is the nature of the image?

List four properties of the image formed by the concave mirror when the object is placed between F & P.

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