What should be the minimum length of the antenna capable of emitting audio signal of wavelength λ?

1. λ
2. λ/2
3. λ/4
4. λ/8

To radiate a signal with good efficiency, the antenna height must be comparable to the wavelength of the signal (≈λ). For efficiency, we take the antenna length to be at least one fourth of the wavelength of the signal, i.e. λ/4.

The correct option is C.