Which of the following is not a factor in determining a transformer’s efficiency?

A transformer's efficiency is primarily influenced by how well it converts input electrical energy into output electrical energy, minimizing losses. The factors that affect efficiency primarily include load current, temperature, and voltage ratios.

Load current is significant because as the load increases, the copper losses (I²R losses) also increase. These losses can impact the overall efficiency of the transformer. Higher load currents generally lead to greater energy losses, thereby affecting efficiency.

Temperature affects a transformer’s efficiency due to its impact on resistance. As a transformer heats up, the resistance of its windings increases, which can lead to higher losses. Therefore, understanding how efficiency changes with temperature is crucial for managing transformer performance under varying operational conditions.

Voltage ratios play a role in efficiency as they are critical for the proper operation of transformers. The ability of a transformer to effectively manage these ratios impacts the amount of power it can transfer without incurring excessive losses.

Physical size may influence a transformer's design and application but does not directly impact its efficiency calculations. Factors like material properties and design configurations—rather than the physical dimensions alone—are more pertinent to efficiency. Hence, identifying physical size as a non-factor in efficiency determination aligns well with the fundamental principles of transformer operation.