Question

When an object is placed at distance of 15 cm from a concave mirror its image is formed at 10 cm in front of the mirror calculate the focal length of the mirror draw a ray diagram.

please give me ray diagram. I will make u brainliest ​

Answer 1

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• Object distance (u) = -15 cm
• Image distance (v) = -10 cm
• Focal length (f) = ? cm

$\bold{{\underline{\red{Formulas}\pink{\:to\:be}\green{\:used}\purple{:-}}}}$

• $\bold{\frac{1}{Image\:distance\:(\frac{1}{v} )}\: +\: \frac{1}{Object\:distance\:(\frac{1}{u} )} \:=\:\frac{1}{Focal\:length\:(\frac{1}{f} )} }$

${\bold{{\underline{\red{Q}\pink{uest}\green{ion}\purple{:-}}}}}$

• To find the focal length of concave mirror ?

${\bold{{\underline{\red{S}\pink{olut}\green{ion}\purple{:-}}}}}$

   ${\bold{{\underline{\red{To}\pink{\:find}\green{\:focal\:length}\purple{:-}}}}}$

• $\bold{\frac{1}{Image\:distance\:(\frac{1}{v} )}\: +\: \frac{1}{Object\:distance\:(\frac{1}{u} )} \:=\:\frac{1}{Focal\:length\:(\frac{1}{f} )} }$

• $\bold{\frac{1}{-10}\: +\: \frac{1}{-15} \:=\:\frac{1}{Focal\:length\:(\frac{1}{f} )}}$

• $\bold{\frac{2\:+\:3}{-30} \:=\:\frac{1}{Focal\:length\:(\frac{1}{f} )}}$

• $\bold{\frac{5}{-30} \:=\:\frac{1}{Focal\:length\:(\frac{1}{f} )}}$

• Focal length = - 6 cm

Answer 2

$\bigstar$ Given :

• An object is placed at distance of 15 cm from a concave mirror and its image is formed at 10 cm in front of the mirror

$\bigstar$ To Find :

Focal length of the mirror

$\bigstar$ Formula Used :

• $\bold{\bf{\red{\frac{1}{f}=\frac{1}{u}+\frac{1}{v} }}}$

where

• f = Focal length of the mirror
• u = Object distance
• v = Image distance

$\bigstar$ Solution :

Object distance , u =  15 cm

Image distance , v =  10 cm

Focal length , f = ? cm

Just sub. these values in the formula

$\implies \bold{\frac{1}{f}=\frac{1}{u} +\frac{1}{v} }\\\\\implies \bold{\frac{1}{f}=\frac{1}{15} +\frac{1}{10} }\\\\\implies \bold{\frac{1}{f}=\frac{(10+15)}{150} }\\\\\implies \bold{\frac{1}{f}=\frac{25}{150} }\\\\\implies \bold{f=6\;cm}$

So , focal length of the concave lens is 6 cm.

Note :

There are different types of sign rules here.

But my sir told simply one thing.

1. For concave mirror we can take both object and image distance as positive and also focal length is positive. Same thing happens to convex lens.
2. Foe convex mirror we can take focal length as negative and object and image distance as positive. Same thing happens to concave lens.

We can use any type of sign rules. But it must be perfect. You can't be unclear about it.