Ohm's law, series and parallel circuits, power, reactance, impedance and three-phase basics.
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- Ohm's law states the relationship between voltage, current, and resistance. What is the formula?
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V = IR (or I = V/R, or R = V/I)- If a 12V source is applied across a 4 ohm resistor, what is the current?
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3 amperes (I = V/R = 12/4)- A circuit draws 5 amperes at 120 volts. What is the total resistance?
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24 ohms (R = V/I = 120/5)- Conductance is the reciprocal of resistance. If R = 5 ohms, what is the conductance?
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0.2 siemens (G = 1/R)- In a series circuit with three resistors (10 ohms, 15 ohms, 20 ohms), what is the total resistance?
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45 ohms (resistances add in series: 10 + 15 + 20)- In a series circuit, how does current behave throughout the circuit?
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Current is the same at all points (same current flows through each resistor)- In a series DC circuit with a 24V source and 6 ohms total resistance, what is the current?
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4 amperes- In a series circuit, voltage drops across a 5 ohm resistor when 2 amperes flows through it. What is that voltage drop?
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10 volts (V = IR = 2 × 5)- In a parallel circuit, how does voltage behave across each branch?
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Voltage is the same across all branches (equal to the source voltage)- In a parallel circuit with branches of 10 ohms and 20 ohms connected to a 120V source, what is the current in the 10 ohm branch?
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12 amperes (I = V/R = 120/10)- Two resistors (4 ohms and 12 ohms) are connected in parallel. What is the equivalent resistance?
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3 ohms (1/RT = 1/4 + 1/12 = 4/12, RT = 3)- In a parallel circuit, total current divides among the branches. If 30A total current flows through two equal branches, how much goes through each?
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15 amperes through each branch- What are the three formulas for calculating electrical power?
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P = VI (volts times current), P = I²R (current squared times resistance), P = V²/R (voltage squared divided by resistance)- A heater draws 10 amperes at 240 volts. How much power does it consume?
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2400 watts (P = VI = 240 × 10)- In AC circuits, real power is the power actually consumed. What unit is it measured in?
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Watts (W)
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