For a 10% voltage boost, how should the secondary coils of a transformer be connected?

When aiming for a 10% voltage boost in a transformer, connecting the secondary coils in series is the effective method. When coils are connected in series, the voltages from each coil add together, which allows for a cumulative voltage increase. This configuration is particularly useful in applications where higher output voltage is required than what is provided by a single coil.

In contrast, connecting the coils in parallel would not achieve a voltage boost; instead, it would maintain the same output voltage as one coil while increasing the current capacity. A loop connection would not effectively increase voltage and is not a standard method for achieving voltage boosts in transformer applications. Connecting coils in reverse typically would not be relevant to voltage boosting; it usually refers to a phasing issue which merely affects the output phase without managing voltage levels.

Therefore, for achieving a specific voltage increase such as a 10% boost, series connections among the secondary coils are necessary and effective.