In an electrical transformer, what is the purpose of the primary coil?

• A. To transform AC into DC.
• B. To receive the input voltage and create a magnetic field.
• C. To increase the output voltage.
• D. To control the load current.

Answer: (B)

The primary coil in an electrical transformer serves the essential function of receiving the input voltage and creating a magnetic field. When alternating current (AC) flows through the primary coil, it generates a magnetic field that surrounds the coil. This changing magnetic field is crucial for transformer operation as it links with the secondary coil, inducing a voltage in it according to Faraday's law of electromagnetic induction. The induced voltage in the secondary coil is dependent on the turns ratio between the primary and secondary coils, which ultimately determines whether the transformer steps up or steps down the voltage.

The primary coil does not serve the purpose of converting AC into DC, as transformers only work with AC due to the necessity of changing magnetic fields for operation. Although transformers can step up or step down voltage, that function is not directly performed by the primary coil alone; it depends on the relationship between the primary and secondary coils. The primary coil also does not control load current; that function is typically managed by other components in the electrical system. Thus, the correct understanding of the primary coil's role focuses on its ability to receive input voltage and establish the magnetic field that facilitates the voltage transfer to the secondary coil.