Question

in a transformer, the iron cores magnetic field changes direction at the same as the current in the coil. this induces an current of the same frequency, but usually not the same, in the secondary coil.

Explanation:

Step1: Analyze the first blank

In a transformer, the magnetic field in the iron core is induced by the current in the primary coil. Since the current in the primary coil is alternating (AC), the magnetic field direction changes at the same frequency as the primary - coil current.

Step2: Analyze the second blank

The coil that provides the input current (the current that creates the changing magnetic field) is the primary coil.

Step3: Analyze the third blank

According to Faraday's law of electromagnetic induction, a changing magnetic field induces an alternating current (AC) in the secondary coil.

Step4: Analyze the fourth blank

In a transformer, the voltage (and thus the current, assuming a resistive load) in the secondary coil is related to the number of turns in the primary and secondary coils by the formula \(\frac{V_s}{V_p}=\frac{N_s}{N_p}\). So, the current magnitude (which is related to voltage and load resistance) in the secondary coil is usually not the same as that in the primary coil, while the frequency remains the same (because the rate of change of the magnetic field, which determines the induced - emf frequency, is set by the primary - coil current frequency).

Answer:

frequency; primary; alternating; magnitude