Circuits, motors and power show up on the Mechanical exam in plain, plug-in form. Learn the handful of relationships and collect the points.
Choose any section below to get a free practice problem. Work it with the FE Reference Handbook open, tap your answer, then check the solution.
Ohm’s law, V = IR, plus two rules covers DC circuits: resistors in series add, and resistors in parallel combine as 1/R = Σ1/Ri.
24 V is applied across a 2 kΩ and a 6 kΩ resistor in series. What is the voltage across the 6 kΩ resistor?
Voltage divider: 24(6/8) = 18 V.
Common trap: (C) is the voltage across the 2 kΩ resistor.
Electrical and Computer EngineeringOhm’s lawKirchhoffThat was 1 of 3 problems in this section. The full course has the lesson, a worked example and every problem. Try all of it free for 3 days →
Capacitors store energy in an electric field (½CV2) and resist sudden changes in voltage.
How much energy does a 100 μF capacitor store at 50 V?
W = ½CV2 = ½(100 × 10−6)(2500) = 0.125 J.
Common trap: (D) forgets the ½.
CapacitorsInductorsRC and RL TransientsThat was 1 of 3 problems in this section. The full course has the lesson, a worked example and every problem. Try all of it free for 3 days →
In AC circuits, resistance becomes impedance Z = R + jX.
What is the reactance of a 50 mH inductor at 60 Hz?
XL = 2πfL = 2π(60)(0.05) = 18.8 Ω.
Common trap: (C) forgets the 2π.
AC Circuitsimpedancepower factorresonanceThat was 1 of 3 problems in this section. The full course has the lesson, a worked example and every problem. Try all of it free for 3 days →
Three-phase power is P = √3 VLIL cos θ using line values.
A three-phase load draws 20 A at 480 V line-to-line with a 0.85 power factor. What is the real power?
P = √3(480)(20)(0.85) = 14.1 kW.
Common trap: (A) omits the √3.
Three-Phasesynchronous speedslipThat was 1 of 3 problems in this section. The full course has the lesson, a worked example and every problem. Try all of it free for 3 days →
Coulomb’s law gives the force between two charges, F = kq1q2/r2 with k = 8.99 × 109 N·m2/C2.
What is the electric field 0.3 m from a 1 μC point charge?
E = kq/r2 = (8.99 × 109)(10−6)/0.09 = 1.0 × 105 N/C.
Common trap: (A) divides by r instead of r2.
ElectrostaticsCoulombMagnetic FieldsThat was 1 of 3 problems in this section. The full course has the lesson, a worked example and every problem. Try all of it free for 3 days →
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