Tube $$A$$ has bolt ends open while tube $$B$$ has one end closed, otherwise they are identical. The ratio of fundamental frequency of tube $$A$$ and $$B$$ is

If a current is passed through a spring then the spring will

A tuning fork arrangement (pair) produces $$4$$ beats/sec with one fork of frequency $$288$$ $$cps.$$ A little wax is placed on the unknown fork and it then produces $$2$$ beats/sec. The frequency of the unknown fork is

If a charge $$q$$ is placed at the center of the line joining two equal charges $$Q$$ such that the system is in equilibrium then the value of $$q$$ is