EST common mistakes
EST · Understand the traps and how to avoid them.
Applying Ohm's law or power formulas by plugging in values without first converting prefixes (k, m, µ, M) to base units, then selecting an answer in the wrong magnitude.
Candidates recognize the formula but treat '4.7 kΩ' as '4.7' and '20 mA' as '20', so the arithmetic is right but the result is off by powers of ten; the distractors are built around exactly these slips.
What to do instead
Before computing, rewrite every given value in base units on scratch paper (4.7 kΩ = 4700 Ω, 20 mA = 0.020 A), then compute, then convert the answer back to the unit the choices use.
Treating series and parallel rules as interchangeable, e.g. adding parallel resistors directly or assuming current is the same everywhere in a parallel network.
The formulas are memorized as isolated facts rather than as consequences of 'same current in series / same voltage in parallel', so mixed networks get simplified incorrectly.
What to do instead
For every network, first mark which nodes share a voltage and which elements share a current, then apply the reciprocal rule only to parallel branches and verify with a quick sanity check (parallel equivalent must be smaller than the smallest branch).
Confusing the reading a meter would display with the quantity being measured, e.g. expecting an ammeter in parallel to read circuit current or assuming a voltmeter has zero resistance.
Candidates learn 'meters measure X' without learning the internal resistance and connection requirements, so they predict the ideal behavior even when the question describes a misconnected meter.
What to do instead
Memorize the pairing: voltmeter in parallel with very high resistance, ammeter in series with very low resistance, ohmmeter across a de-energized isolated component; when a question describes a wrong connection, reason about the loading effect rather than the ideal reading.
Reading an oscilloscope trace without accounting for probe attenuation and time/div or volts/div settings, reporting the screen height instead of the actual voltage.
The trace 'looks like' the answer, so candidates skip the scale multiplication step, and 10x probes make the factor-of-ten error especially common.
What to do instead
Always state the conversion explicitly: peak-to-peak voltage = vertical divisions × volts/div × probe factor; period = horizontal divisions × time/div; then convert period to frequency. Write the multiplication out rather than eyeballing.
Mixing decibel ratios, treating a 3 dB change as a doubling of power and a 6 dB change as a doubling of voltage interchangeably, or adding dB gains linearly.
The dB is a logarithmic ratio and candidates carry over linear intuition; the 3 dB/6 dB distinction (power vs. voltage/amplitude) is a frequent trap.
What to do instead
Anchor on the definitions: dB = 10 log(P2/P1) = 20 log(V2/V1). Memorize that +3 dB doubles power, +6 dB doubles voltage, +10 dB is ten times power; combine cascaded stages by adding dB values, not multiplying them.
Selecting a transmission line or antenna answer based only on frequency while ignoring impedance matching, cable loss, or connector type.
Candidates focus on the headline number (frequency or length) and overlook that the practical answer depends on matching and loss at that frequency.
What to do instead
For any RF cabling or antenna question, check three things in order: characteristic impedance match (e.g. 50 Ω source, line, load), loss per unit length at the operating frequency, and connector suitability; eliminate choices that violate matching before comparing the rest.
Confusing fiber connector types and polish styles (SC vs. LC vs. ST; UPC vs. APC) or mating incompatible polish styles, and misidentifying single-mode vs. multimode by connector rather than by core size.
Connector shape is visually memorable while polish and core size are abstract, so candidates pattern-match on the wrong feature.
What to do instead
Learn the pairs as a table: LC = small form factor latch, SC = square push-pull, ST = bayonet; UPC = flat/angled-free, APC = angled green; single-mode ≈ 9 µm core, multimode 50/62.5 µm. Classify by core size and polish, never by connector body.
Diagnosing a fault by swapping parts before performing a structured measurement sequence (power check, then signal tracing from source to load).
Under time pressure, replacing suspected components feels faster than measuring, and a lucky fix reinforces the habit without teaching the fault location.
What to do instead
Use a fixed sequence: verify supply voltage at the source, then at each node toward the load, comparing against expected values; isolate by splitting the circuit in half (half-split method) rather than guessing. Document the measurement at each step.
Overlooking high-voltage hazards or lockout/tagout steps when a question describes servicing equipment, choosing the 'fast' troubleshooting action over de-energizing and verifying.
The technically correct repair path competes with a plausible shortcut, and candidates answer as technicians rather than as safety-first responders.
What to do instead
Adopt the rule that any servicing scenario begins with de-energize, lock/tag, verify absence of voltage, and discharge stored energy; if an answer skips verification of dead condition, eliminate it regardless of how efficient it sounds.
Applying a standard or best practice from the wrong context, e.g. citing a residential wiring rule for a telecom or fiber installation, or treating a manufacturer recommendation as a code requirement.
Candidates memorize rules without their scope, so a rule that is correct in one domain is misapplied in another, and the distinction between 'code requires' and 'best practice recommends' is blurred.
What to do instead
For each rule you study, record its scope (what equipment, what environment) and its status (mandated vs. recommended). When a question names a specific environment, filter out rules whose scope does not match before choosing.