B

Step 1: Understand the concept of eddy currents. Eddy currents are loops of electric current that are induced within conductors by a changing magnetic field. These currents create energy losses in the form of heat due to the resistance of the material.
Step 2: Eddy currents can be minimized by using a laminated core. Laminating the core material reduces the size of the loops of eddy currents, as each layer is insulated from the others, thereby increasing the resistance to the flow of these currents.
Step 3: Analyze the options:
- Option A: Increasing the number of turns in the secondary coil does not reduce eddy currents; it affects the voltage and current but not the core losses.
- Option B: Correct. By using a laminated core, we reduce eddy currents.
- Option C: A step-down transformer relates to the voltage transformation ratio and does not specifically address eddy currents.
- Option D: Using a weak alternating current at high potential does not effectively address the issue of eddy currents either.
Conclusion: Therefore, the best option is B, as laminated cores are a well-known technique for reducing eddy current losses in transformers.