Question

The coil of a choke in a circuit (a) Increase the current (b) Decrease the current (c) Does not change the current (d) Has high resistance to a circuit

Short answer

Based on the analysis, the coil of a choke in a circuit can (a) increase the current, (b) decrease the current, or (d) have high resistance to a circuit depending on the choke's specific scenario. However, option (c) does not change the current is less likely as chokes typically affect the current passing through them in some way.

Step-by-step solution

Understanding a choke (inductor)

A choke, which is an inductor, stores energy in the form of a magnetic field when current passes through it. In a circuit, a choke allows lower frequency (or direct current) to pass smoothly, while it obstructs (or chokes) higher-frequency alternating current (AC). This behavior can have different results in a circuit as mentioned below. 2.

Analyzing the effect on the current#a

If the coil of a choke in a circuit is used to (a) increase the current, it means that more direct current is supplied to the choke. Since a choke allows low frequency or direct current to pass through without much hindrance, as the direct current increases, the choke doesn't pose much resistance, and the current increases as well. 3.

Analyzing the effect on the current#b

If the coil of a choke in a circuit is used to (b) decrease the current, it means that either the direct current supplied to it is reduced or the frequency of the alternating current is increased. When the direct current is decreased, the choke allows the remaining current to pass through, subsequently decreasing the overall current in the circuit. Similarly, when the frequency of the AC increases, the choke's impedance increases, creating more resistance for the AC current, which leads to a decrease in the overall current. 4.

Analyzing the effect on the current#c

If the coil of a choke in a circuit (c) does not change the current, it would mean that the choke's presence in the circuit does not affect the current passing through it either way. This situation can happen when a choke is in resonance with an applied frequency or the AC current provided to it has no frequency component that the choke would obstruct. 5.

Analyzing the effect on the current#d

If the coil of a choke in a circuit (d) has high resistance, it would mean that the impedance offered by the choke is high for the particular frequency applied to it. When this happens, the choke obstructs the AC current, allowing a smaller current to pass through, which would be observed as a high resistance in the circuit. From the above analysis, we can conclude that (a) Increase the current, (b) Decrease the current, and (d) Has high resistance to a circuit, all describe different scenarios where a choke's behavior in a circuit is affected. But option (c) Does not change the current is less likely to happen as chokes will always have some effect on the current passing through them.

Key concepts

AC and DC currents

Electrical circuits can be powered by either Alternating Current (AC) or Direct Current (DC). Depending on the type of current, the behavior of components like an inductor can vary significantly. Direct Current refers to electrical flow that is unidirectional, meaning it doesn’t change direction over time, such as with a battery. In contrast, Alternating Current is characterized by its ability to change direction periodically, like the electricity found in household outlets.

A choke, primarily an inductor, is highly sensitive to these differences. With DC current, a choke offers minimal resistance, permitting it to pass almost unhindered. Essentially, the wired coil in an inductor doesn’t resist DC flow, making it an excellent choice for filtering out unwanted frequencies in some instances.

However, with AC the situation changes. Here, a choke can affect the current flow based on the frequency of the alternating signal. Because the choke exhibits different impedance depending on the frequency, it can restrict AC currents more significantly than DC, especially at higher frequencies.

Inductor Impedance

Impedance is the resistance that an inductor shows to the flow of electric current in a circuit. Unlike simple resistors, which have a constant resistance, an inductor's impedance depends greatly on the frequency of the current passing through it.

The relation of impedance in inductors is expressed by the formula: \[ Z = j \omega L \] where:

• Z is the impedance
• \(\omega\) is the angular frequency of the current
• L is the inductance of the coil
• j is the imaginary unit \(\sqrt{-1}\)

The higher the frequency of the AC, the greater the impedance becomes. This is due to the inductor creating a magnetic field that opposes the change in current. Essentially, as the frequency increases, more of the AC is obstructed, causing the choke to act as a bottleneck.

Magnetic Field in Inductors

At the core of how inductors work is their ability to generate a magnetic field when current flows through the coil. This magnetic field stores energy, allowing the inductor to affect the current in the circuit.

When an AC current passes through an inductor, the magnetic field is constantly changing, which creates inductance. This change is key to how inductors can filter out certain frequencies of electrical signals. Inductors capture energy during one phase of AC's cycle and release it during another, impacting the current flow.

The magnetic field's strength in an inductor depends on factors like the number of turns in the coil and the current's intensity. More loops in the coil or higher currents generate a stronger magnetic field. Inductors utilize this property for energy storage and frequency filtering, vital elements in many electronic devices.

Frequency Response of Inductors

Inductors have a unique response to frequencies in the circuits they are part of, which is crucial in their operation and application. This frequency response refers to how well an inductor can react to varying frequencies of an electromagnetic signal.

In general terms, an inductor will allow low-frequency signals to pass more smoothly, making them valuable in blocking high-frequency noise. As the frequency of a signal increases, the inductance causes higher impedance, reducing the current that can pass through.

The resonance frequency is a point of specific interest, where the inductive reactance can match other reactive components in the circuit, like capacitors. At this particular frequency, the opposing reactive power becomes balanced, resulting in maximum or minimum impedance depending on the design.

This property of frequency response is especially useful in tuning circuits, radio transmitters, and transformers, where clear signal filtering and frequency selection are necessary.