Question

An object is placed at a distance of 20cm from a convex lens
of focal length 15cm. A real and inverted image is formed at a distance
of 35cm on the other side of the lens. Find its magnification.

options

a...+1.75cm
b...+0.57 cm
c....-1.75cm
d...-0.57m​

Answer 1

Given:

• Object Distance ,u = -20 cm

• Focal Length ,f = 15 cm

• Image distance ,v = 35 cm

To Find:-

• Magnification ,m

Solution:-

As we know that magnification is defined as the ratio of height of image to the ratio of height of object.

❒ m = v/u

where,

m denotes magnification

v denotes image distance

u denotes object distance

Substitute the value we get

→ m = 35/(-20)

→ m = -35/20

→ m = -1.75

Therefore, magnification of the lens is -1.75 .

Hence, the required answer is (c) -1.75 .

Answer 2

Answer:

Given :-

• An object is placed at a distance of 20 cm from a convex lens of focal length of 15 cm.
• A real and inverted image is formed at a distance of 35 cm on the other side of the lens.

To Find :-

• What is the magnification.

Formula Used :-

We know that,

$\boxed{\bold{\large{m\: =\: \dfrac{v}{u}}}}$

where,

• m = Magnification
• v = Distance of the image
• u = Object distance

Solution :-

Given :

• Object distance = - 20 cm
• Distance of the image = 35 cm

According to the question by using the formula we get,

⇒ $m\: =\: \dfrac{35}{- 20}$

➠ $m\: =\: -\: 1.75$

$\therefore$ The magnification of the lens is - 1.75. Hence, the correct options is option no (c) - 1.75.