Question

The length of a vertical stick at the surface of the lake appears 12cm to a fish under water. If refractive index of water is 4/3 then actual length of stick above water is

• A. $16cm$
• B. $9cm$
• C. $12cm$
• D. $3cm$

Answer 1

The correct option is B $9cm$

$ApparentDepthorHeight=\frac{ActualDepthorheight}{Refractiveindexofmedium1w.r.t2}\text{Height in the given case is going from}\text{air to water}\text{Medium 1 - air}\text{Medium 2 - water}Apparentlength=\frac{\text{actual length}}{n_{aw}}{n}_{aw}=\frac{n_a}{n_w}=\frac{1}{n_w}Apparentlength=\frac{Actuallength}{n_{aw}}ApparentLength=\frac{\text{Actual length}}{\frac{1}{n_w}}\text{Apparent length}=actuallength\times n_{w}12=l\times \frac{4}{3}l=\frac{12\times 3}{4}l=9cm$