Conceptual Actual Emended Exam Questions
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1. What does the time constant (τ) represent in an RC circuit?
ANSWER The time it takes for the voltage across the capacitor to charge
or discharge to about 63% of its final value.
2. A 1 µF capacitor is connected in series with a 100 kΩ resistor. What is the
time constant?
ANSWER τ = 100,000 × 0.000001 = 0.1 seconds
3. You are taking a night call and your troubleshooting leads you to find a
burnt out resistor. The original resistor was 215Ohms. You do not have a
215Ohm resistor on site. Which combination of resistors could you use to
get the car running again? - ANSWER 90Ohm, 75Ohm, and 50Ohm
wired in series
4. If a gearless machines drive sheave has a circumferance of 6 feet,
approximately how many RPMs would be required of the drive motor to
run 800fpm - ANSWER 133
,5. In an RC discharge circuit, what is the voltage across the capacitor after one
time constant?
ANSWER About 37% of the initial voltage.
6. If an RC circuit has a 0.47 µF capacitor and a 220 kΩ resistor, what is the
time constant?
ANSWER τ = 220,000 × 0.00000047 = 0.1034 seconds
7. What is the formula for the time constant of an RC circuit?
ANSWER τ=R×C
(τ in seconds, R in ohms, C in farads)
8. In a series RC circuit, how much voltage remains across the capacitor after 5
time constants during discharge?
ANSWER Less than 1% — the capacitor is considered fully discharged
after 5τ.
9. You are putting up a stringer of lights in a hoist way with lights spaced at 6
foot intervals. If using 100 watt light bulbs, how many feet of the houstway
can you cover before tripping the breaker on a 20A circuit? - ANSWER
144 feet
10.What happens to the charging rate of a capacitor if the resistance is
increased?
ANSWER The capacitor charges more slowly because the time constant
increases.
,11.How does a capacitor behave at the moment a DC voltage is applied in an
RC circuit?
ANSWER It initially acts like a short circuit, allowing maximum current
to flow.
12.How does a capacitor behave after a long time in a steady-state DC circuit?
ANSWER It acts like an open circuit—no current flows through it.
13.What tool would you use to visually observe the voltage changes across a
capacitor in real-time?
ANSWER An oscilloscope.
14.What is the unit of capacitance?
ANSWER Farad (F)
15.What effect does reducing the resistance in an RC charging circuit have?
ANSWER It shortens the time constant, causing the capacitor to charge
faster.
16.What electrical value is calculated by multiplying resistance (in ohms) by
capacitance (in farads)?
ANSWER The time constant (τ) of an RC circuit
17.What is the maximum amount of resistance that would be found on a 4.7K
ohm resistor with 20% tolerance? - ANSWER 3760 ohms
, 18.All electrical tools should be checked... - ANSWER regularly
19.The ____ is the same across all branches of a parallel circuit. - ANSWER
voltage
20.The ease with which magnetic lines of force distrubute themselves
throughout a material is known as ____ - ANSWER Permeability
The point at which a given piece of material contains all the lines of force it can
hold is called ____. - ANSWER Saturation
Current flows from left to right on a conductor, what is true of the magnetic lines
of force? - ANSWER The magnetic lines of force will be in the
counterclockwise direction.
____ measures current in a circuit without disconnecting wires. - ANSWER
Clamp-on meter
The moveable portion of a relay is referred to as the ____ - ANSWER
Armature
The period of a sine wave is .0083 seconds. What is the frequency? - ANSWER
120 Hz
f= 1/t