A student attaches one end of a Slinky to the top of a table. She holds the other end in her hand, stretches it to a length ℓ, and then moves it back and forth to send a wave down the Slinky.

The student attaches one end of a slinky to the top of a table.

The student holds the other end of the slinky.

The slinky stretches the length of .

The speed of the wave along the Slinky depends upon the mass of the Slinky and the tension caused by stretching it.

Since this has not changed, the wave speed remains constant.

The wave speed can also be written as the product of the wavelength and frequency.

Therefore, as the frequency is increased, the wavelength must decrease.

The option (a) is correct.