Ham Radio General Class Practice Test

What is the turns ratio of a transformer used to match an audio amplifier having a 600-ohm output impedance to a speaker having a 4-ohm impedance?

1. 12.2 to 1

2. 24.4 to 1

3. 150 to 1

4. 300 to 1

The correct answer is: 12.2 to 1

The turns ratio of a transformer can be calculated using the formula that relates the impedance on both sides of the transformer, which is as follows: \[ \text{Turns Ratio} = \sqrt{\frac{Z_{primary}}{Z_{secondary}}} \] In this case, the primary side of the transformer is connected to the audio amplifier, which has a 600-ohm output impedance. The secondary side is connected to the speaker, which has a 4-ohm impedance. Using the values: \[ \text{Turns Ratio} = \sqrt{\frac{600 \, \text{ohms}}{4 \, \text{ohms}}} \] Calculating that gives: \[ \text{Turns Ratio} = \sqrt{150} \approx 12.25 \] This turns ratio of approximately 12.2 to 1 indicates that for every 12.2 turns of wire on the primary side, there will be one turn on the secondary side. This configuration is appropriate for matching the impedances of the audio amplifier and speaker, ensuring that maximum power transfer occurs from the amplifier to the speaker. Other options do not reflect the correct calculations for the impedance transformation and thus result in inaccurate turns