The frequency of a stretched uniform wire of length $L$ under tension is in resonance with the fundamental frequency of a closed pipe of same length. If the tension in the wire is increased by 8 N , it is in resonance with the first overtone of the same closed pipe. The initial tension in the wire is

In the following circuit shown in figure, three diodes are connected each with forward resistance $40 \Omega$ and infinite backward resistance. The current through $100 \Omega$ resistance is

Three concentric charged metallic spherical sheets $A, B$ and $C$ have radii $a, b, c$ potentials $V_A$, $\mathrm{V}_{\mathrm{B}}, \mathrm{V}_{\mathrm{C}}$ and charge densities $+\sigma,-\sigma$ and $+\sigma$ respectively. The value of potential $\mathrm{V}_{\mathrm{A}}$ is ( $\varepsilon_0=$ permittivity of free space)

On a photosensitive material, when frequency of incident radiation is increased by $20 \%$, maximum kinetic energy of emitted photoelectrons increases from 0.4 eV to 0.7 eV . The work function of the material is