Final answer:
Antennas must be a specific length that correlates with the frequency of the electromagnetic waves they are designed to receive or emit, typically as a specific multiple of the wavelength (¼, ½, etc.) for efficient operation.
Step-by-step explanation:
The length of an antenna is critical for its function. The correct answer is b) No, antennas must be a specific length based on the frequency of the electromagnetic waves they are meant to receive or transmit. The most efficient length for a transmitting antenna is often ½ (lambda over two), half the wavelength of the electromagnetic wave it is designed to emit. For a receiving antenna, while a wide variety of lengths can work, designing it to be a specific multiple of the wavelength (such as ¼ or ½) allows for more efficient pickup of the signal.
For example, if a broadcast antenna is ideal at one-fourth its wavelength, and the antenna is 50.0 meters high, it suggests that it broadcasts most efficiently at a frequency where the wavelength is 200 meters, which falls within the AM frequency band. In practice, the dimensions of an antenna must often correspond to specific multiples of the wavelength associated with the frequency for resonant effects, which is essential for both efficient radiation of energy (in transmitting antennas) and sensitivity to incoming signals (in receiving antennas).