Question

In an experiment to determine the focal length of a converging lens, the object distance and the image distance recorded were 20 cm and 30 cm respectively. What is the focal length of the converging lens?
A) 10 cm B) 12 cm C) 15 cm D) 18cm

Answer 1

Here is the answer for your question.....

Answer 2

Given:

• The object distance = 20 cm
• The image distance = 30 cm

To Find:

• The focal length of the converging lens.

Solution:

We know a formula which is to object image, real image, and focal length, and is given by,

1/-u + 1/-v = 1/-f → {equation 1}

Where "u" is the object image, "v' is the real image and "f" is the focal length.

On substituting the values in equation 1 we get,

⇒ 1/-20+1/-30=1/-f  {eliminating negative sign}

⇒ 1/f = 1/20 + 1/30  {taking LCM, LCM = 600}

In the above step we took LCM of 20 and 30 which is 600 and multiplied the LCM individually to each fraction to add them further.

⇒ 1/f = (30+20)/600  {adding the terms in bracket}

⇒ 1/f = 50/600 = 1/12  {dividing the terms and inversing the fractional value}

⇒ f = 12 cm

∴ The focal length of the converging lens = 12 cm