1
WB JEE 2026
MCQ (Single Correct Answer)
+1
-0.25
Change Language

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 ‘

A

$\left[\frac{2 d \rho}{g\left(\rho-\rho^{\prime}\right)}\right]^{\frac{1}{2}}$

B

$\left[\frac{2 g d}{\rho\left(\rho-\rho^{\prime}\right)}\right]^{\frac{1}{2}}$

C

$\left[\frac{2 d \rho^{\prime}}{\rho g\left(\rho-\rho^{\prime}\right)}\right]^{\frac{1}{2}}$

D

$\left[\frac{g\left(\rho-\rho^{\prime}\right)}{2 d \rho}\right]^{\frac{1}{2}}$

2
WB JEE 2026
MCQ (Single Correct Answer)
+1
-0.25
Change Language

Beyond what distance,the ray optics is sufficiently valid when the aperture is 6 mm wide and the wavelength is $6000 \mathop {\rm{A}}\limits^{\rm{o}}$ ?

A

50 m

B

40 m

C

60 m

D

10 m

3
WB JEE 2026
MCQ (Single Correct Answer)
+1
-0.25
Change Language

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

A

$\frac{R}{\left(\mu_1-\mu_2\right)}$

B

$\frac{2 R}{\left(\mu_1-\mu_2\right)}$

C

$\frac{R}{2\left(\mu_1+\mu_2\right)}$

D

$\frac{R}{2\left(\mu_1-\mu_2\right)}$

4
WB JEE 2026
MCQ (Single Correct Answer)
+1
-0.25
Change Language

Consider a fuse wire of length $l$ and radius $r$ .The time of heating $(t)$ for passing the maximum current will depend on

A

$t \propto r^2 l$

B

$t \propto r^3 l^2$

C

$t \propto r^4 l^0$

D

$t \propto r^2 l^3$