Using a convex lens a clear image of a candle
flame is produced on a screen. How many
other clear images can be received on this
screen if only the lens is to be shifted?
(A) A large number
(B) Only one more
(C) Two more
(D) None
Explain with solution.
Dear Student,
When the object is placed at infinity :
1. The image will form at the principal focus (F).
2. The image will be real and inverted.
3. The image will be very small in size.
When the object is placed beyond 2F :
1. The image will form between F and 2F.
2. The image will be real and inverted.
3. The image will be smaller in size.
When the object is placed at 2F :
1. The image will form at 2F.
2. The image will be real and inverted.
3. The image will be equal in the size of object.
When the object is placed between F and 2F :
1. The image will form beyond 2F.
2. The image will be real and inverted.
3. The image will be magnified.
When the object is placed at F :
1. The image will form at infinity.
2. The image will be real and inverted.
3. The image will be highly magnified.
When the object is placed between the pole (P) and F :
1. The image will form on the same side of object.
2. The image will be virtual and erect.
3. The image will be magnified.
When the object is placed at infinity :
1. The image will form at the principal focus (F).
2. The image will be real and inverted.
3. The image will be very small in size.
When the object is placed beyond 2F :
1. The image will form between F and 2F.
2. The image will be real and inverted.
3. The image will be smaller in size.
When the object is placed at 2F :
1. The image will form at 2F.
2. The image will be real and inverted.
3. The image will be equal in the size of object.
When the object is placed between F and 2F :
1. The image will form beyond 2F.
2. The image will be real and inverted.
3. The image will be magnified.
When the object is placed at F :
1. The image will form at infinity.
2. The image will be real and inverted.
3. The image will be highly magnified.
When the object is placed between the pole (P) and F :
1. The image will form on the same side of object.
2. The image will be virtual and erect.
3. The image will be magnified.
According to above discussion the convex lens produces magnified and clear image of an object in 3 cases,
• when object is at between pole and focus
• when object us placed between F and 2F
• when the object is placed at 2F
The lens also produces the magnified image when the object is at focus (F), but in this case image is highly magnified which make the image less clearer.
Hence, the convex lens can produce two more clear images of candle(excluding the image formation of candle before the shifting of the lens) if the lens is shifted (option C).
Regards