Two waves of same frequency ($n$) approaching each other with same velocity of $18$ m/s interfere. The distance between two consecutive antinodes is

The equation of a progressive wave is given by $y = 6\cos(100t - 4x)$ where $y$ is in $\mu\text{m}$, $x$ in metre and $t$ in second. The ratio of the maximum particle velocity to the velocity of wave is

A body sends a wave $150$ mm long through medium P and $0.30$ m long in medium Q. If velocity of the wave in medium P is $80\,\text{cm s}^{-1}$, the velocity of wave in medium Q is

An uniformly charged thin spherical shell of radius 'R' has uniform surface charge density '$\sigma$'. It is made of two hemispherical identical shells held together by pressing them with force 'F' as shown. F is proportional to
[$\epsilon_0$ = permittivity of free space]