Beyond what distance,the ray optics is sufficiently valid when the aperture is 6 mm wide and the wavelength is $6000 \mathop {\rm{A}}\limits^{\rm{o}}$ ?
50 m
40 m
60 m
10 m
A plano-convex lens fits exactly into a plano-concave lens.Their plane surfaces are parallel to each other.If lenses are made of different materials of refractive indices $\mu_1$ and $\mu_2$ and $R$ is the radius of curvature of the curved surface of the lenses,then the focal length of the combination is
$\frac{R}{\left(\mu_1-\mu_2\right)}$
$\frac{2 R}{\left(\mu_1-\mu_2\right)}$
$\frac{R}{2\left(\mu_1+\mu_2\right)}$
$\frac{R}{2\left(\mu_1-\mu_2\right)}$
Consider a fuse wire of length $l$ and radius $r$ .The time of heating $(t)$ for passing the maximum current will depend on
$t \propto r^2 l$
$t \propto r^3 l^2$
$t \propto r^4 l^0$
$t \propto r^2 l^3$
Density and volume of a body are given as $(20 \pm 4) \mathrm{gm} / \mathrm{cm}^3$ and $(10 \pm 1) \mathrm{cm}^3$ respectively. The absolute error in measurement of mass is
20 gm
30 gm
45 gm
60 gm
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