Question

किसी 20 सेंटीमीटर फोकस दूरी के उत्तल लेंस के संपर्क में रखे 30 सेंटीमीटर फोकस दूरी के अवतल लेंस के संयोजन से बने संयुक्त लेंस की फोकस दूरी क्या है क्या यह संयोजक अभिसारी लेंस है अथवा अवतारी​

Answer 1

Answer:

your answer is given in the above photo

Answer 2

SOLUTION

GIVEN

A concave lens of 30 cm focus distance placed in contact with a convex lens of 20 cm focus distance

TO DETERMINE

• The focus distance of the combined lens

• Whether this combination is convergent lens or divergent

EVALUATION

Here it is given that a concave lens of 30 cm focus distance placed in contact with a convex lens of 20 cm focus distance

We know that Focus distance of a convex lens is positive and of concave lens is negative

$\sf{f_1 = Focus \: distance \: of \: concave \: lens = - 30}$

$\sf{f_2= Focus \: distance \: of \: convex \: lens = + 20}$

Let f = The focus distance of the combined lens

We are aware of the formula that

$\displaystyle \sf{ \frac{1}{f} = \frac{1}{f_1 } + \frac{1}{f_2 } }$

$\displaystyle \sf{ \implies \: \frac{1}{f} = \frac{1}{ - 30 } + \frac{1}{20 } }$

$\displaystyle \sf{ \implies \: \frac{1}{f} = - \frac{1}{ 30 } + \frac{1}{20 } }$

$\displaystyle \sf{ \implies \: \frac{1}{f} = \frac{ - 2 + 3}{60} }$

$\displaystyle \sf{ \implies \: \frac{1}{f} = \frac{ 1}{60} }$

$\displaystyle \sf{ \implies \: f = 60 }$

The focus distance of the combined lens = 60 cm

Again

Power of the concave lens

$\displaystyle \sf{P_1 = - \frac{1}{0.30} = - \frac{10}{3} }$

Power of the convex lens

$\displaystyle \sf{P_2 = \frac{1}{0.20} = 5 }$

So the power of the combined lens P is given by

$\displaystyle \sf{P = P_1 +P_2 }$

$\displaystyle \sf{ \implies \: P = - \frac{10}{3} + 5 }$

$\displaystyle \sf{ \implies \: P = \frac{ - 10 + 15}{3} }$

$\displaystyle \sf{ \implies \: P = + \frac{ 5}{3} }$

Since focus distance and power of the combined lens are both positive

So combined lens is convergent

FINAL ANSWER

• The focus distance of the combined lens = 60 cm

• The combined lens is convergent

━━━━━━━━━━━━━━━━

Learn more from Brainly :-

1. find the speed of sound in air at 50 degree C and 70 dgree C (take speed of sound 332m/s)

https://brainly.in/question/40606714

2. A simple pendulum has period 4 s. The length of the string of the pendulum will be (take g = 10 m/s2 and 1T2 = 10)

https://brainly.in/question/36767516