Total internal reflection of light is possible when light enters from

The area (in square units) of the region enclosed by the two circles $x^2+y^2=1$ and $(x-1)^2+y^2=1$ is

Which one of the following is a slime mould?

The figure shows the variation of photocurrent with anode potential for a photo-sensitive surface for three different radiations. Let $I_a, I_b$ and $I_c$ be the intensities and $f_a, f_b$ and $f_c$ be the frequencies for the curves $a, b$ and $c$ respectively.

When a capacitor is connected in series to an $LR$ circuit,the alternating current flowing in the circuit

For the alkali metals,which of the following increases with increasing atomic number?