Final answer:
To calculate the output voltage of a transformer, divide the input voltage by the ratio of the number of turns in the primary coil to the number of turns in the secondary coil, known as the transformer equation.
Step-by-step explanation:
To calculate the output voltage of a transformer, you must divide the input voltage by the transformer's turns ratio, specifically the ratio of the number of turns in the primary coil to the number of turns in the secondary coil. This relationship is known as the transformer equation, which states that the ratio of the secondary voltage to the primary voltage is equal to the ratio of the number of turns in the secondary coil to the number of turns in the primary coil. This means, for example, if a transformer steps down the voltage from 1200V to 120V and has 1000 turns in the primary coil, then it would need 100 turns in the secondary coil to give that reduced voltage. Some transformers can increase the voltage (step-up transformer), while others decrease it (step-down transformer). Regardless of this, the electrical power output is nearly equal to the power input given a high efficiency, often exceeding 99%. Hence, if we ignore resistance, the power equations would be Pp = IpVp = IsVs = Ps, where P stands for power, I for current, V for voltage, p for primary coil, and s for secondary coil.