Every object has a natural frequency of vibration. If kinetic energy is applied to an object at a rate that matches its natural frequency, resonance occurs and the object vibrates. In this experiment a small current, produced by a signal generator, causes the sonometer wire to move up and down due to interaction with the magnetic field of a U-shaped magnet. When the rate of movement due to the current matches the fundamental frequency of the wire, resonance occurs causing noticeable vibration. If the tension on the wire is increased (length kept constant), the resonant frequency of the wire also increases.
On graph paper, draw a graph of frequency against the square root of the tension(x-axis). Start both axes at zero.
A straight line graph through the origin shows that frequency is proportional to square root of tension.