Question

Capacitance of a capacitor made by a thin metal foil is $2\mu F$. If the foil is folded with paper of thickness 0.15 mm, dielectric constant of paper is 2.5 and width of paper is 400 mm, the length of the foil will be :

• A. 0.34 m
• B. 1.33 m
• C. 13.4 m
• D. 33.9 m

Answer 1

The correct option is D 33.9 m

Here, let the length be $l$

width is, $b=400mm=0.4m$

thickness, $t=0.15mm=15\times {10}^{-5}m$

As capacitance for parallel plate capacitor is,

$C=K{ϵ}_{0}A/d=K{ϵ}_0(l\times b)/t$

$⟹l=Ct/K{ϵ}_{0}b=2\times {10}^{-6}\times 15\times {10}^{-5}/(2.5\times 8.85\times {10}^{-12}\times 0.4)=33.91m$

Option D is correct.