A postage stamp kept below a rectangular glass block of refractive index $1.5$ when viewed from vertically above it, appears to be raised by $7.0 m m$ . Calculate the thickness of the glass block.

1.2 c m

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4.2 c m

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2.1 c m

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3 c m

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Solution

The correct option is C $2.1 c m$
Refractive Index $= \frac{r e a l d e p t h}{a p p a r e n t d e p t h}$

If thickness of glass block is $x$ ; real depth= $x$ and apparent depth = $x - 7$

$\Rightarrow 1.5 = \frac{x}{x - 7}$

$\Rightarrow 1.5 (x - 7) = x$

$\Rightarrow 1.5 x - 10.5 = x$

$\Rightarrow 0.5 x = 10.5$

$\Rightarrow x = \frac{10.5}{0.5} = 21 m m$

Therefore, thickness of glass block $x$ is 21 mm or 2.1 cm.

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A postage stamp kept below a rectangular glass block of refractive index 1.5 when viewed from vertically above it, appears to be raised by 7.0 mm. Calculate the thickness of the glass block.

The correct option is C 2.1 cmRefractive Index =real depthapparent depthIf thickness of glass block is x; real depth=x and apparent depth = x−7⇒1.5=xx−7⇒1.5(x−7)=x⇒1.5x−10.5=x⇒0.5x=10.5⇒x=10.50.5=21mmTherefore, thickness of glass block x is 21 mm or 2.1 cm.

A postage stamp kept below a rectangular glass block of refractive index $1.5$ when viewed from vertically above it, appears to be raised by $7.0 m m$ . Calculate the thickness of the glass block.