05: Refraction Through A Lens : Icse-x-physics

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ICSE-X-Physics

05: Refraction through a Lens

with Solutions - page 4

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Section : C

Qstn #1
What are the three principal rays that are drawn to construct the ray diagram for the image formed by a lens? Draw diagrams to support your answer.
Ans : 1 (i) A ray of light incident at the optical centre O of the lens passes undeviated through the lens.

(ii) A ray of light incident parallel to the principal axis of the lens, after refraction passes
through the second focus F₂ (in a convex lens) or appears to come from the second focus F₂ (in a concave lens).

(iii) A ray of light passing through the first focus F₁ (in a convex lens) or directed towards the first focus F₁ (in a concave lens), emerges parallel to the principal axis after refraction.

Qstn #2
In the diagram below, XX' represents the principal axis, O the optical centre and F the focus of the lens. Complete the path of rays A and B as they emerge out of the lens.

Ans : 2

Distinguish between a real and a virtual image.

Ans : 3

Real Image	Virtual Image
A real image is formed due to actual intersection of refracted (or reflected) rays.	A virtual image is formed when the refracted (or reflected) rays meet if they are produced backwards.
A real image can be obtained one a screen.	A virtual image cannot be obtained on a screen.
A real image is inverted with respect to the object.	A virtual image is erect with respect to the object

Qstn #4
Study the diagram (Fig.) given below.

Ans : 4

#4-a
Name the lens LL'
Ans : LL' lens is convex lens.

#4-b
What are the points O and O' called?
Ans : O and O' are known as first and second focal points respectively.

#4-c
Complete the diagram to form the image of the object AB.
Ans :

#4-d
state the three characteristics of the image.
Ans : The image formed will be magnified, virtual and upright.

#4-e
Name a device in which this action of lens is used.
Ans : Such action of lens is used in a magnifying glass.

Qstn #5
Study the diagram (Fig.) below.
(i) Name the lens LL’ (ii) what are the points O, O'called? (iii) Complete the diagram to form the image of the object AB. (iv) State three characteristics of the image.
Ans : 5 (i) LL' is concave lens.
(ii) The points O and O' are called second and first focal points respectively.
(iii)

(iv) The three characteristics of the image are:
Virtual
Erect
Diminished

Qstn #6
Study the diagram shown in Fig.
Ans : 6

#6-a
Complete the diagram to show the formation of image A'B' of the object AB of same size.
Ans : Complete diagram for the formation of A'B'.

#6-b
Name the lens LL' and draw its outline.
Ans : LL' is a convex lens which is drawn as

#6-c
what are the points O and O'called?
Ans : O and O' are called as first and second focal points respectively.