If $\left(4^{\sec ^2 \alpha}\right) x^2+2 x+\left(\beta^2-\beta+\frac{1}{2}\right)=0$ has real roots,then the value/values of $\left(\cos \alpha+\cos ^{-1} \beta\right)$ is/are
$1+\frac{\pi}{3}$ ,if $n$ is even.
$-1-\frac{\pi}{3}$ ,if $n$ is odd.
$-1+\frac{\pi}{3}$ ,if $n$ is odd.
$-1+\frac{\pi}{3}$ ,if $n$ is even.
A body of density'$\rho$'is dropped slowly on the surface of a lake of depth $d$ .If the density of the lake water be'$\rho^{\prime \prime}\left(\rho^{\prime}<\rho\right)$ then the time taken by the body to reach the bottom of the lake is ‘
$\left[\frac{2 d \rho}{g\left(\rho-\rho^{\prime}\right)}\right]^{\frac{1}{2}}$
$\left[\frac{2 g d}{\rho\left(\rho-\rho^{\prime}\right)}\right]^{\frac{1}{2}}$
$\left[\frac{2 d \rho^{\prime}}{\rho g\left(\rho-\rho^{\prime}\right)}\right]^{\frac{1}{2}}$
$\left[\frac{g\left(\rho-\rho^{\prime}\right)}{2 d \rho}\right]^{\frac{1}{2}}$
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
$\frac{R}{\left(\mu_1-\mu_2\right)}$
$\frac{2 R}{\left(\mu_1-\mu_2\right)}$
$\frac{R}{2\left(\mu_1+\mu_2\right)}$
$\frac{R}{2\left(\mu_1-\mu_2\right)}$
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