IMSA TRAFFIC SIGNAL TECHNICIAN VERIFIED ANSWERS AND
QUESTIONS - MOST RECENT EDITION 2026/2027
Q: What is Ohm's Law? ANSWER V = I x R (Voltage equals Current
multiplied by Resistance).
Q: What is the formula for electrical power? ANSWER P = V x I (Power
equals Voltage multiplied by Current).
Q: In a series circuit, what remains constant? ANSWER Current.
Q: In a parallel circuit, what remains constant? ANSWER Voltage.
Q: How do you calculate total resistance in a series circuit? ANSWER
Add all individual resistances together (Rt = R1 + R2 + R3...).
Q: What is the purpose of a transformer in a traffic signal cabinet?
ANSWER To step down high voltage (120/240V) to low voltage (120V or
less) for the controller and components.
Q: What does a capacitor do in an AC circuit? ANSWER It stores
electrical energy and can cause a phase shift between voltage and
current.
Q: What is a diode used for? ANSWER To allow current to flow in only
one direction (rectification).
Q: What is the function of a transistor? ANSWER To amplify a weak
signal or act as an electronic switch.
Q: What is inductance? ANSWER The property of a conductor or coil
that opposes any change in current flow.
Q: What is reactance? ANSWER The opposition to current flow offered
by capacitors (capacitive reactance) and inductors (inductive reactance)
in AC circuits.
Q: What is impedance? ANSWER The total opposition to current flow in
an AC circuit, combining resistance and reactance.
Q: If a 120V circuit has a total resistance of 12 ohms, what is the
current? ANSWER 10 Amps (I = V/R).
,Q: What happens to total resistance if you add another resistor in
parallel? ANSWER Total resistance decreases.
Q: What is a short circuit? ANSWER An unintended low-resistance path
that allows excessive current to flow, potentially causing damage or
fire.
Q: What is an open circuit? ANSWER A break in the circuit path that
stops current flow.
Q: What is the unit of capacitance? ANSWER Farad.
Q: What is the unit of inductance? ANSWER Henry.
Q: What does AC stand for? ANSWER Alternating Current.
Q: What does DC stand for? ANSWER Direct Current.
Q: What is the standard frequency of AC power in the US? ANSWER 60
Hertz (Hz).
Q: What is a ground fault? ANSWER An unintentional electrical
connection between a current-carrying conductor and ground.
Q: What device protects a circuit from overcurrent? ANSWER A fuse or
circuit breaker.
Q: What is a relay? ANSWER An electromechanical switch that uses a
low-power signal to control a high-power circuit.
Q: What are the normally open (NO) and normally closed (NC) contacts
on a relay? ANSWER NO contacts are open when the relay is de-
energized; NC contacts are closed when de-energized.
Q: What is a Zener diode used for? ANSWER Voltage regulation.
Q: What is an LED? ANSWER Light Emitting Diode.
Q: Why are LEDs preferred over incandescent bulbs in traffic signals?
ANSWER They use less power, last longer, and are more visible.
Q: What is a voltmeter used to measure? ANSWER Voltage (potential
difference).
Q: What is an ammeter used to measure? ANSWER Current
(Amperage).
, Q: What is an ohmmeter used to measure? ANSWER Resistance
(Ohms).
Q: How should a voltmeter be connected in a circuit? ANSWER In
parallel.
Q: How must an ammeter be connected in a circuit? ANSWER In series.
Q: What is a multimeter? ANSWER A device that combines voltmeter,
ammeter, and ohmmeter functions.
Q: What is a semiconductor? ANSWER A material (like silicon) that has
electrical conductivity between a conductor and an insulator.
Q: What is an SCR (Silicon Controlled Rectifier)? ANSWER A solid-state
device used for switching and controlling high-current AC loads.
Q: What is the purpose of a varistor (MOV)? ANSWER To suppress
voltage spikes and protect circuits from surges.
Q: What is true power measured in? ANSWER Watts.
Q: What is apparent power measured in? ANSWER Volt-Amps (VA).
Q: What is reactive power measured in? ANSWER Volt-Amps Reactive
(VAR).
Q: What is the power factor? ANSWER The ratio of true power to
apparent power (Watts / VA).
Q: What type of wire is best for high-frequency applications? ANSWER
Coaxial cable.
Q: What is skin effect? ANSWER The tendency of AC current to flow
near the surface of a conductor at high frequencies.
Q: What is a three-phase power system? ANSWER A system with three
AC voltages offset by 120 degrees.
Q: What is the voltage between phases in a 120/208V three-phase
system? ANSWER 208 Volts.
Q: What is a bridge rectifier? ANSWER A circuit of four diodes used to
convert AC to DC.
Q: What is an opto-isolator? ANSWER A device that uses light to
transfer electrical signals between isolated circuits.
QUESTIONS - MOST RECENT EDITION 2026/2027
Q: What is Ohm's Law? ANSWER V = I x R (Voltage equals Current
multiplied by Resistance).
Q: What is the formula for electrical power? ANSWER P = V x I (Power
equals Voltage multiplied by Current).
Q: In a series circuit, what remains constant? ANSWER Current.
Q: In a parallel circuit, what remains constant? ANSWER Voltage.
Q: How do you calculate total resistance in a series circuit? ANSWER
Add all individual resistances together (Rt = R1 + R2 + R3...).
Q: What is the purpose of a transformer in a traffic signal cabinet?
ANSWER To step down high voltage (120/240V) to low voltage (120V or
less) for the controller and components.
Q: What does a capacitor do in an AC circuit? ANSWER It stores
electrical energy and can cause a phase shift between voltage and
current.
Q: What is a diode used for? ANSWER To allow current to flow in only
one direction (rectification).
Q: What is the function of a transistor? ANSWER To amplify a weak
signal or act as an electronic switch.
Q: What is inductance? ANSWER The property of a conductor or coil
that opposes any change in current flow.
Q: What is reactance? ANSWER The opposition to current flow offered
by capacitors (capacitive reactance) and inductors (inductive reactance)
in AC circuits.
Q: What is impedance? ANSWER The total opposition to current flow in
an AC circuit, combining resistance and reactance.
Q: If a 120V circuit has a total resistance of 12 ohms, what is the
current? ANSWER 10 Amps (I = V/R).
,Q: What happens to total resistance if you add another resistor in
parallel? ANSWER Total resistance decreases.
Q: What is a short circuit? ANSWER An unintended low-resistance path
that allows excessive current to flow, potentially causing damage or
fire.
Q: What is an open circuit? ANSWER A break in the circuit path that
stops current flow.
Q: What is the unit of capacitance? ANSWER Farad.
Q: What is the unit of inductance? ANSWER Henry.
Q: What does AC stand for? ANSWER Alternating Current.
Q: What does DC stand for? ANSWER Direct Current.
Q: What is the standard frequency of AC power in the US? ANSWER 60
Hertz (Hz).
Q: What is a ground fault? ANSWER An unintentional electrical
connection between a current-carrying conductor and ground.
Q: What device protects a circuit from overcurrent? ANSWER A fuse or
circuit breaker.
Q: What is a relay? ANSWER An electromechanical switch that uses a
low-power signal to control a high-power circuit.
Q: What are the normally open (NO) and normally closed (NC) contacts
on a relay? ANSWER NO contacts are open when the relay is de-
energized; NC contacts are closed when de-energized.
Q: What is a Zener diode used for? ANSWER Voltage regulation.
Q: What is an LED? ANSWER Light Emitting Diode.
Q: Why are LEDs preferred over incandescent bulbs in traffic signals?
ANSWER They use less power, last longer, and are more visible.
Q: What is a voltmeter used to measure? ANSWER Voltage (potential
difference).
Q: What is an ammeter used to measure? ANSWER Current
(Amperage).
, Q: What is an ohmmeter used to measure? ANSWER Resistance
(Ohms).
Q: How should a voltmeter be connected in a circuit? ANSWER In
parallel.
Q: How must an ammeter be connected in a circuit? ANSWER In series.
Q: What is a multimeter? ANSWER A device that combines voltmeter,
ammeter, and ohmmeter functions.
Q: What is a semiconductor? ANSWER A material (like silicon) that has
electrical conductivity between a conductor and an insulator.
Q: What is an SCR (Silicon Controlled Rectifier)? ANSWER A solid-state
device used for switching and controlling high-current AC loads.
Q: What is the purpose of a varistor (MOV)? ANSWER To suppress
voltage spikes and protect circuits from surges.
Q: What is true power measured in? ANSWER Watts.
Q: What is apparent power measured in? ANSWER Volt-Amps (VA).
Q: What is reactive power measured in? ANSWER Volt-Amps Reactive
(VAR).
Q: What is the power factor? ANSWER The ratio of true power to
apparent power (Watts / VA).
Q: What type of wire is best for high-frequency applications? ANSWER
Coaxial cable.
Q: What is skin effect? ANSWER The tendency of AC current to flow
near the surface of a conductor at high frequencies.
Q: What is a three-phase power system? ANSWER A system with three
AC voltages offset by 120 degrees.
Q: What is the voltage between phases in a 120/208V three-phase
system? ANSWER 208 Volts.
Q: What is a bridge rectifier? ANSWER A circuit of four diodes used to
convert AC to DC.
Q: What is an opto-isolator? ANSWER A device that uses light to
transfer electrical signals between isolated circuits.
