Question

An object is placed 60cm from concave lens.the image is formed at a distance 20cm from the optical center.find the focal length of the lens.is the lens converging or diverging​

Answer 1

Answer:

f = -30

Since the focal length is negative. It is a diverging lens.

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Answer 2

Answer :

›»› The focal length of the lens is -30 cm and it is diverging lens.

Given :

• Object distance = -60 cm
• Image distance = -20 cm

To Calculate :

• Focal length = ?

How to Calculate?

❒ Here in this question we have to calculate the focal length of the lens is the lens converging or diverging. So we will use the lens formula which says 1/v - 1/u = 1/f

Here,

• v is the Image distance in cm.
• u is the Object distance in cm.
• f is the Focal length in cm.

So let's Calculate Focal length...

Calculation :

→ u = -60 cm (It is to the left of lens)

→ v = -30 cm (It is to the left of lens)

→ f = ?

From lens formula

$\tt{: \implies \dfrac{1}{v} - \dfrac{1}{u} = \dfrac{1}{f} }$

⠀

$\tt{: \implies \dfrac{ - 1}{20} - \dfrac{ - 1}{60} = \dfrac{1}{f} }$

⠀

$\tt{: \implies \dfrac{ - 3 + 1}{60} = \dfrac{1}{f} }$

⠀

$\tt{: \implies \cancel{\dfrac{ - 2}{60}} = \dfrac{1}{f} }$

⠀

$\tt{: \implies -\dfrac{1}{ 30} = \dfrac{1}{f} }$

⠀

$\frak{: \implies \underline{ \boxed{ \pink{ \frak{f = -30 \: cm}}}}}$

⠀

║Hence, the focal length of the lens is -30 cm and it is diverging lens.║