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CBSE Class 10 Answered

<div>&nbsp;</div> <div> <h3 class="f18" style="padding: 0px; margin: 0px; border: 0px; outline: 0px; vertical-align: baseline; font-family: Lato, Arial, Helvetica, sans-serif; color: #53555b; font-size: 17px !important; font-stretch: normal !important; background-image: initial; background-attachment: initial; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;"> <p style="padding: 0px; margin: 0px; border: 0px; outline: 0px; vertical-align: baseline; background: transparent;"><span style="padding: 0px; margin: 0px; border: 0px; outline: 0px; vertical-align: baseline; background: transparent;">An object is placed 10 cm from a diverging lens which forms an image 6.5 cm from the lens. What is the focal length of the lens?<br style="padding: 0px; margin: 0px;" /></span></p> </h3> </div>
Asked by RAHUL rd | 22 Nov, 2014, 10:33: PM
Expert Answer
Given that:
The object distance,u = -10cm
The image distance ,v= -6.5 cm
Let f be the focal length of the lens.
According to lens formula we know that:

begin mathsize 14px style 1 over straight f equals 1 over straight v minus 1 over straight u 1 over straight f equals fraction numerator 1 over denominator minus 6.5 end fraction minus fraction numerator 1 over denominator minus 10 end fraction 1 over straight f equals fraction numerator minus 10 minus minus 6.5 over denominator minus 6.5 cross times minus 10 end fraction equals fraction numerator minus 3.5 over denominator 65 end fraction straight f space equals minus 18.6 space cm end style

Given that it is a diverging lens ,i.e. concave lens.The focal length of a concave lens is - ve.
So the focal length of the lens =-18.6 cm
Answered by Jyothi Nair | 22 Nov, 2014, 11:59: PM
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