The correct answer is A. Radio frequency.
A tuned amplifier is an amplifier that is designed to amplify a specific frequency or range of frequencies. It does this by using a tuned circuit, which is a circuit that resonates at a specific frequency. The tuned circuit is used to select the desired frequency or range of frequencies, and the amplifier then amplifies the selected frequencies.
Tuned amplifiers are used in a variety of applications, including radio receivers, transmitters, and amplifiers. They are also used in some types of test equipment.
A tuned amplifier is not used in low frequency applications because the tuned circuit would be too large and bulky. A tuned amplifier is also not used in audio frequency applications because the tuned circuit would be too sensitive to noise.
Here is a brief explanation of each option:
- Option A: Radio frequency. A tuned amplifier is used in radio frequency applications because it can amplify a specific frequency or range of frequencies.
- Option B: Low frequency. A tuned amplifier is not used in low frequency applications because the tuned circuit would be too large and bulky.
- Option C: Audio frequency. A tuned amplifier is not used in audio frequency applications because the tuned circuit would be too sensitive to noise.
- Option D: None of the above. This option is incorrect because a tuned amplifier is used in radio frequency applications.