A Pipe open at one end has length $0.8$ m. At the open end of the tube a string $0.5$ m long is vibrating in its first overtone and resonates with fundamental frequency of pipe. If tension in the string is $50$ N, the mass of string is (Neglect end correction) (Speed of sound $= 320$ m/s)

A sonometer wire resonates with $4$ antinodes between the two bridges for a given tuning fork when $1$ kg mass is suspended from the wire. Using same fork, when mass M is suspended, the wire resonates producing $2$ antinodes between the two bridges. (Distance between the bridges as before) The value of M is

The fundamental frequency of sonometer wire is $50$ Hz for some length and tension. If the length is increased by $25\%$ by keeping the tension same, then the frequency change of second harmonic is

The number of lines of force originating from a point charge of $2 \times 8.85 \times 10^{-9}$ C in a medium of dielectric constant $10$ is ($\epsilon_0 = 8.85 \times 10^{-12}$ SI unit)