A resonance column apparatus consists of a vertical glass tube partially filled with water, the lower end of the tube being closed by the water surface. A tuning fork of frequency 512 Hz is held above the open end. Resonance is first obtained when the length of the air column is 18 cm and again when it is 56 cm.
(i) Determine the wavelength of the sound in air.
(ii) Hence calculate the speed of sound in air under the laboratory conditions.