Advertisements
Advertisements
Question
A pin 2 cm long is placed 12 cm away from a convex lens at right angles to the principal axis. If the focal length of the lens is 20 cm, by scale drawing find the size of the image and its magnification.
Solution
Given O = 2 cm, u = 12 cm, f = 20 cm
I = ?, M = ?
Taking the scale of measurement are : 2 cm = 1 cm on the graph.
In the drawing,
O = 1cm, u = 6cm, f = 10 cm
From the drawing,
I = 2.7 cm
⇒ actual image size I = 2.7 x 2 = 5.4 cm
Magnification m = `"I"/"O" = 5.4/2` = 2.7 cm
APPEARS IN
RELATED QUESTIONS
(a) Draw a ray diagram to show the formation of an image by a convex lens when an object is placed in front of the lens between its optical centre and principal focus.
(b) In the above ray diagram, mark the object distance (u) and the image distance (v) with their proper signs (+ve or –ve as per the new Cartesian sign convention) and state how these distances are related to the focal length (f) of the convex lens in this case.
(c) Find the power of a convex lens which forms a real and inverted image of magnification –1 of an object placed at a distance of 20 cm from its optical centre.
Which of the following lenses would you prefer to use while reading small letters found in a dictionary?
"A lens can form a magnified erect image as well as magnified inverted image of an object placed in front of it." State the nature of this lens and draw ray diagrams to justify the above statement. Mark the positions of O, F and 2F in the diagram.
A beam of light travelling in a rectangular glass slab emerges into air. Draw a ray-diagram indicating the change in its path.
A ray of light travelling in water emerges into air. Draw a ray-diagram indicating the change in its path.
Draw a labelled ray diagram to show how a ray of light passes through a parallel sided glass block:
if it hits the glass block at 90° (that is, perpendicular to the glass block)
Draw a labelled ray diagram to show how a ray of light passes through a parallel sided glass block:
if it hits the glass block at an angle other than 90° (that is, obliquely to the glass block).
Where should an object be placed in order to use a convex lens as a magnifying glass?
Show by a diagram the refraction of two light rays incident parallel to the principal axis on a convex lens by treating it as a combination of a glass slab and two triangular glass prisms.
A concave mirror and convex lens are held in water. What changes, if any, do you expect in their focal length?
