What is the maximum angle of incidence $\theta_i$ in the figure for which the ray would satisfy the condition for total internal reflection at the boundary of media of refractive indices $n_1$ and $n_2$, where $n_1>n_2$ ?

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$$ \text { What is the equivalent resistance between the points } A \text { and } B \text { in the figure? } $$

Consider a solid rod of mass $m$ and uniform density resting against a vertical wall and horizontal floor as shown in the figure. The coefficients of friction of the rod with the wall and with the floor are given to be $\mu_1$ and $\mu_2$ respectively. Gravity is acting downwards with acceleration due to gravity $g$. What should be the value of the inclination angle $\alpha$ so that the rod stays in equilibrium?

The charge distribution inside a sphere of radius $R=2 a / b$ is given by the volume charge density $\rho=a r^2-b r^3$, where $a$ and $b$ are constants and $r$ is the radial distance from the center of the sphere. At what distance from the center of the sphere, will the electric field go to zero?