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Image By Convex Lens

A convex lens can form real or virtual images depending on where the object is placed.

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Student-friendly explanation

If the object is beyond the focus, the lens usually forms a real image on the other side. If the object is between the focus and the lens, the image is virtual, erect, and enlarged on the same side. This chapter concept is often tested through ray diagrams and image-formation tables.

How to write this in exams

  1. 1

    Start with the exact idea

    A convex lens can form real or virtual images depending on where the object is placed.

  2. 2

    Then show how to use it

    1. Locate the object relative to F and 2F. 2. Use the standard rays. 3. Predict image position, nature, and size. 4. Check whether the image is real or virtual.

  3. 3

    Add one concrete example

    An object placed beyond 2F gives a real inverted diminished image between F and 2F.

  4. 4

    Avoid this incomplete answer

    Saying a virtual image forms on the opposite side of the lens. For a convex lens, a virtual image forms on the same side as the object.

Definition

A convex lens can form real or virtual images depending on where the object is placed.

Example

An object placed beyond 2F gives a real inverted diminished image between F and 2F.

Rule to remember

A ray parallel to the principal axis passes through the focus, and a ray through the optical centre goes undeviated.

Memory hook

Beyond focus, image on the other side; within focus, image on the same side.

Examples and method

Worked example

If an object is beyond 2F, the image forms between F and 2F on the other side, and it is real, inverted, and smaller than the object.

Method to apply

1. Locate the object relative to F and 2F. 2. Use the standard rays. 3. Predict image position, nature, and size. 4. Check whether the image is real or virtual.

Diagram support

Draw the principal axis, optical centre, focal points F and 2F, then trace the two standard rays from the object.

How CBSE asks it

Questions ask you to predict image nature from object position or to draw the ray diagram for a convex lens.

Avoid common mistakes

Common confusion

Students often think every convex lens image is real. A convex lens can also form a virtual image when the object is within the focal length.

Common wrong answer

Saying a virtual image forms on the opposite side of the lens. For a convex lens, a virtual image forms on the same side as the object.

Exam tip

Remember the standard image table for convex lenses; it saves time in both theory and ray-diagram questions.

Quick check

When an object is placed between the focus and a convex lens, what kind of image is formed?

A virtual, erect, and enlarged image is formed on the same side of the lens as the object.

Study the image by convex lens diagram carefully

Use the labelled diagram to keep image by convex lens clear in short answers and revision.

What this diagram makes clear

This diagram keeps the labels and direction of image by convex lens in the right order.

Where this helps in exams

Use this for labelled diagram work and short exam answers on image by convex lens.

Revision cue

Revise image by convex lens through the labels before writing the answer.

Answer writing and exam use

1-mark answer

A convex lens can form real or virtual images depending on where the object is placed.

2-mark answer

A convex lens can form real or virtual images depending on where the object is placed. A ray parallel to the principal axis passes through the focus, and a ray through the optical centre goes undeviated. An object placed beyond 2F gives a real inverted diminished image between F and 2F.

3-mark answer

If the object is beyond the focus, the lens usually forms a real image on the other side. If the object is between the focus and the lens, the image is virtual, erect, and enlarged on the same side. This chapter concept is often tested through ray diagrams and image-formation tables. A ray parallel to the principal axis passes through the focus, and a ray through the optical centre goes undeviated. If an object is beyond 2F, the image forms between F and 2F on the other side, and it is real, inverted, and smaller than the object. Questions ask you to predict image nature from object position or to draw the ray diagram for a convex lens. Saying a virtual image forms on the opposite side of the lens. For a convex lens, a virtual image forms on the same side as the object.
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