Circuits and Magnetism

An electrical technician connects a $12\text{ V}$ DC battery across the primary winding of an iron-core transformer through a switch. After the switch is closed and a steady current is established in the primary winding, what voltage behavior is observed across the secondary winding?

A technician sets up an experiment with two electrically isolated wire coils wrapped around a shared soft-iron core. Coil 1 is connected in series with a $12\text{ V}$ DC power supply and a mechanical switch. Coil 2 is connected directly to a sensitive center-zero galvanometer. The switch is closed and kept closed until current stabilizes, after which the switch is abruptly opened. What behavior will the galvanometer display during the period of steady current and at the exact instant the switch is opened?

A DC power supply is connected across a series circuit containing two resistive components. Fill in the blanks with the correct numerical values to complete the circuit analysis.

A transformer can continuously induce a voltage in its secondary winding when powered by a steady, unchanging direct current (DC) source.

Inserting a soft iron core into the center of an energized coil of wire increases the overall strength of the magnetic field compared to an air-core coil with the same current and number of turns.

A direct-current power distribution box supplies power to two parallel branches. The first branch has a resistance of $20\ \Omega$, and the second branch has a resistance of $5\ \Omega$. What is the total equivalent resistance of the network?

When the direct current flowing through an inductor decreases, the self-induced electromotive force (counter-EMF) acts in the same direction as the original current to oppose the reduction in current flow.

A direct current (DC) circuit consists of a $48\text{ V}$ power supply connected in series with three resistors: $R_1 = 12\ \Omega$, $R_2 = 24\ \Omega$, and $R_3 = 24\ \Omega$. In its baseline operating state, the total circuit resistance is $R_T = 60\ \Omega$ and the circuit loop current is $I = 0.8\text{ A}$.

Match each circuit alteration on the left to its corresponding electrical outcome on the right.

A direct-current marine radio circuit contains two resistors connected in parallel: a $10\ \Omega$ resistor and a $40\ \Omega$ resistor. What is the total equivalent resistance of this parallel circuit, in ohms?

Which of the following occurs when a direct current flows through an insulated wire coiled around a soft-iron core?

When the direct current flowing through an energized inductor coil is suddenly interrupted by opening a switch, a high-voltage spark often arcs across the switch contacts. Which electromagnetic effect causes this sudden voltage surge?

A naval vessel alarm panel is powered by a $72\text{ V}$ DC supply connected in series with three resistive loads: an alert strobe ($R_1 = 8\ \Omega$), an auxiliary buzzer ($R_2 = 10\ \Omega$), and a line-balancing resistor ($R_3 = 6\ \Omega$). What is the voltage drop across the auxiliary buzzer ($R_2$)?

An industrial security monitoring loop is powered by a $36\text{ V}$ DC power supply connected in series with a current-limiting resistor $R_1 = 150\ \Omega$, an optical sensor module $R_2$, and a line termination resistor $R_3 = 250\ \Omega$. When the circuit is active, a voltmeter measures a $12\text{ V}$ drop across the optical sensor module $R_2$. What is the electrical resistance of the optical sensor module $R_2$?

An aircraft instrument panel contains three identical $12\ \Omega$ indicator lights connected in parallel across a direct-current power bus. What is the total equivalent resistance of this parallel circuit?

During the calibration of a naval radar control system, engineers measure a continuous current of $1.5\text{ A}$ flowing through a series safety loop. The loop is energized by a $60\text{ V}$ direct current source and contains three elements: a $15\ \Omega$ current-limiting resistor ($R_1$), a calibration rheostat ($R_2$), and a primary sensor coil ($R_3$). If the primary sensor coil dissipates exactly $36\text{ W}$ of power, what is the required resistance of the calibration rheostat ($R_2$)?

Match each electromagnetic device on the left with its correct operating principle or primary functional description on the right.

An electronics technician is analyzing the operational principles of a DC series circuit. Match each series circuit characteristic on the left with its correct electrical rule or behavioral description on the right.

A $24\text{ V}$ DC power supply energizes a circuit consisting of a $100\,\Omega$ series resistor ($R_1$) connected in series with a parallel network composed of two $200\,\Omega$ branch loads. Under normal operating conditions, the circuit draws $120\text{ mA}$, dropping $12\text{ V}$ across $R_1$ and $12\text{ V}$ across the parallel network. During a troubleshooting check, a technician records a total circuit current of $80\text{ mA}$, a voltage drop of $8\text{ V}$ across $R_1$, and a voltage drop of $16\text{ V}$ across the parallel network. Which fault condition in the circuit explains these diagnostic readings?

A specialized weather station telemetry circuit is powered by a $96\text{ V}$ direct current (DC) power source connected in series with four resistive components: a surge-limiting resistor $R_1 = 18\ \Omega$, a status indicator $R_2 = 27\ \Omega$, a variable humidity sensor $R_3$, and a reference resistor $R_4 = 15\ \Omega$. A technician measures the voltage drop across the status indicator ($R_2$) to be $21.6\text{ V}$. What is the resistance of the humidity sensor $R_3$ in ohms ($\Omega$)?

An electronics technician is analyzing a circuit where a heavy-duty relay coil is controlled by a mechanical switch connected to a 24V DC power supply. Every time the switch is opened to turn off the relay, a visible spark arcs across the switch contacts, eventually causing them to fail. What electromagnetic principle primarily causes this arcing, and how does the coil's magnetic field behave to produce it?