Liang is working with an electrical circuit. she replaces a straight electrical wire with a coiled wire. a. increase the strength of the magnetic field when current flows through the circuit b. decrease the strength of the magnetic field when current flows through the circuit c. increase the current that flows through the wire when the circuit is active d. decrease the current that flows through the wire when the circuit is active

The correct answer is D. Decrease the current that flows through the wire when the circuit is active.

Explanation:

The question did not specify if the current flowing through the circuit is AC or DC. However, we are going to consider the electric circuit in two-state assuming the electric wire is insulated;

First state- when the electric wire is straight

Second state-when the electric wire is coiled.

For DC Current

The DC flowing through the electric wire remains the same whether the electric wire is straight or coiled. The magnetic field generated by the DC when the wire is coiled has little effect on the flow of DC since the magnetic flux produced is constant and not changing. You will need a changing magnetic flux to induce a voltage in the coil by way of electromagnetic induction.

For AC Current

The AC flowing through the coiled wire decreases when compared to that flowing through the straight wire, this is because the coiled wire now acts as an inductor. An inductor usually allows the flow of DC while preventing the flow of AC. When AC is about to flow through the coil, the magnetic field generated by the current cuts across the other windings (other turns of the coil) causing as an induced voltage by way of electromagnetic induction. The induced voltage will tend to oppose the flow of the AC.

Another way of explaining it is that of reactance. The reactance of a coil is frequency-dependent as the frequency increases the reactance of a coil increase.

X = 2πfL

Where f = Frequency and L =Inductance and X = reactance of the coil

Z = R + X  

Where Z = Impedance, R = Resistance and X = Reactance

The impedance of a coil is made up of resistance and reactance. The frequency of DC is zero (f=0) so its reactance is zero (X =0) so it can flow easily through the coil the same cannot be said for an AC. The reactance of an AC is not zero but rather the reactance increases with an increase in frequency. As the reactance increases the impedance also increase thereby resisting the free flow of AC through the inductor.

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