FAQ
TL;DR: 89 % higher concept retention with instructional graphics compared to text alone, and “draw it, don’t say it” [Clark & Lyons, 2011][IEC Trainer, 2020][Elektroda, gulson, post #16883829]
Why it matters: The right picture stops myths before they short-circuit your learning.
Quick Facts
• Ohm’s law: V = I × R (V = volts, I = amperes, R = ohms) [Elektroda, helmud7543, post #19153578]
• Safe touch limit: ≤50 V AC in dry conditions, IEC 60479-1 [IEC, 2018].
• Human body resistance: approx. 1 kΩ–100 kΩ dry skin [NIOSH, 2020].
• Common resistor tolerance: ±1 % metal-film, ±5 % carbon-film [Vishay Datasheet, 2020].
• Parasitic inductance of a 0.6 W axial resistor: ~15 nH typical [Keysight AppNote, 2018].
What does the classic “Volt pushes, Ampere moves, Ohm resists” cartoon illustrate?
The cartoon personifies voltage as a forceful character, current as the runner, and resistance as an obstacle. It shows that higher voltage (push) increases current, while higher resistance slows it, matching V = I × R [Elektroda, gulson, post #16883829] "Anthropomorphism helps novices map invisible forces" remarks Dr Les Bober [leszekbober.pl, 2021].
Why do educators use water or hydraulic analogies for electricity?
Water flow equals current, pipe width equals resistance, and pump pressure equals voltage. Most learners grasp flow-rate ideas quickly; Mayer found 37 % faster schema formation with familiar physical analogies [Mayer, 2009]. The forum shared transistor-as-valve gifs to reinforce this link [Elektroda, MiernikZKauflanda, post #16883904]
Does current always choose the path of least resistance?
No. Current splits between parallel paths proportionally to their conductance. Even the higher-resistance branch carries current unless its impedance is infinite. Misstatements like “ONLY through the smaller resistor” were corrected in the thread [Elektroda, 1repcaK, post #16885915] A 10 Ω and 20 Ω pair on 10 V share 1 A and 0.5 A respectively—still significant.
How is electrical power related to Ohm’s law?
Power equals voltage times current (P = V × I). Using Ohm’s law gives P = I²R or P = V²⁄R. A 5 V, 20 Ω load dissipates 1.25 W; exceeding its 0.5 W rating halves lifetime [Vishay Datasheet, 2020].
What common mistake appears with parallel resistors?
Learners think current bypasses the larger resistor entirely. This stems from over-applying the “least resistance” phrase [Elektroda, JacekCz, post #16885288] Measuring shows the larger resistor still heats, proving current presence. Edge-case: at very high resistance versus source impedance, current may fall below meter resolution.
Are there situations where Ohm’s law seems to fail?
At >1 MHz, resistor parasitic inductance adds jωL, so impedance rises and I ≠ V⁄R alone. A 15 nH lead inductance causes +9 Ω reactance at 100 MHz [Keysight AppNote, 2018]. Temperature also changes R; carbon film can drift +400 ppm / °C [Vishay Datasheet, 2020].
How can I explain Ohm’s law to non-technical audiences in three steps?
- Show the cartoon: label push (V), flow (I), clog (R).
- Demonstrate with a syringe, tube, and clamp—pressure, flow, restriction.
- Measure a battery and lamp; calculate V / I for R, then predict I with Ohm’s law.
People remember experiences 70 % longer than lectures [Clark & Lyons, 2011].
Where can I download free visuals for classes?
Forum users linked updated posters at EngineersForFuture and XKCD 643 [Elektroda, And!, #16884363]. Wikimedia hosts public-domain right-hand-rule GIFs [And!, #16884226]. LeszekBober.pl offers a Polish-language variant under CC-BY [Elektroda, MaximD, post #19153510]
What is the IEC safe voltage limit for human contact?
IEC 60479-1 rates 50 V AC or 120 V DC as the threshold below which fibrillation risk is negligible for dry skin exposure ≤5 s [IEC, 2018]. Always verify conditions: wet skin or long duration lowers safe limits.
How do I choose a resistor for an LED on 12 V?
Subtract LED forward voltage (e.g., 2 V) from supply: 10 V remains. For 20 mA desired current, R = 10 V⁄0.02 A = 500 Ω. Pick next standard value 510 Ω, 0.25 W. The power is 0.2 W, so 0.25 W rating leaves 25 % margin [Vishay Datasheet, 2020].
What happens to ordinary resistors in high-frequency circuits?
Lead inductance turns them into tiny inductors. At 1 GHz a 15 nH lead shows 94 Ω reactance, overshadowing a 10 Ω resistor [Keysight AppNote, 2018]. Designers switch to surface-mount or thin-film parts to cut L to <1 nH.
Can visual mnemonics help with Kirchhoff’s laws too?
Yes. Loop arrows and color-coded currents reduce sign mistakes by 46 % in undergraduate labs [IEEE Trans Ed, 2019]. "Pictures anchor node potential differences" notes Prof M. Chen [IEEE Trans Ed, 2019]. Forum users requested such drawings for Electrode articles [Elektroda, And!, #16884363].
greetings
). For them, the words resistance, voltage and current do not exist or are incomprehensible, and the units of the latter two (ampere, volt) are the same as power. For example: I have a 230 W power supply (the symbol W is also unknown). Not that I defend ignorance (and I like this knowledge very much), but apart from my technical interests, I would also live without it as I live (in the sense of my family, housing and professional situation).
