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Quizzes > Electronics & Gadgets

60 Hz let go threshold and cardiac current quiz

Quick, free physics quiz on AC cardiac thresholds. Instant results.

Editorial: Review CompletedCreated By: Only MilanUpdated Aug 28, 2025
Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art layers depict low current electrical circuits lightning bolt safety protocol icons on dark blue quiz backdrop.

This quiz helps you understand 60 Hz current perception and the let-go threshold, so you can spot which milliamp shock levels need extra care when working around AC. For related practice, try the dysrhythmia quiz and compare effects at other frequencies in the high frequency current quiz.

What is the approximate AC current threshold at 60 Hz that most people can first perceive as a tingling sensation?
5 mA
0.1 mA
10 mA
1 mA
At around 1 mA of 60 Hz AC current flowing through the body, most individuals feel a faint tingling. Currents below this level are typically imperceptible. This threshold is widely used in safety standards..
What is the 'let-go' threshold for AC current, above which a person may be unable to release an energized object?
20 mA
2 mA
5 mA
10 mA
The 'let-go' threshold for 60 Hz AC is about 10 mA, where muscle contractions prevent voluntary release. Below this current, people can usually let go. This is an important safety boundary in electrical protection..
Which protective device is designed to trip when it detects a leakage current exceeding approximately 5 mA?
Transformer
Circuit Breaker
Fuse
Ground Fault Circuit Interrupter (GFCI)
GFCIs (also known as RCDs) monitor imbalance between hot and neutral conductors. If leakage exceeds roughly 5 mA, indicating current flowing through an unintended path, they trip. This helps prevent shock hazards..
At approximately what AC current level does ventricular fibrillation become likely in an adult?
100 mA
50 mA
500 mA
5 mA
Ventricular fibrillation threshold for 60 Hz AC in adults is near 100 mA. Below this, muscular and respiratory effects occur. Above, the heart is more prone to VF..
True or False: A 1 mA DC current is more dangerous than a 1 mA 60 Hz AC current for inducing ventricular fibrillation.
False
True
AC at 60 Hz is more effective at inducing ventricular fibrillation than DC at the same current amplitude. DC requires higher currents to cause fibrillation. Thus 1 mA DC is less dangerous in this context..
Which physiological effect is associated with approximately 30 mA of 60 Hz AC current through the chest?
Respiratory paralysis
No effect
Skin burn only
Perception only
Around 30 mA can paralyze the respiratory muscles temporarily, leading to breathing difficulty. This falls between the muscular contraction and VF threshold. Protection against this level is critical..
Which of the following has the lowest electrical resistance, facilitating higher current flow into the body?
Wet skin
Fat tissue
Bone
Dry skin
Wet skin has a much lower resistance than dry skin, bone, or fat, allowing more current to pass. This greatly increases shock risk if the skin is wet. Safety standards assume wet-skin conditions for worst-case analysis..
Which frequency is considered most hazardous for inducing ventricular fibrillation in humans?
1 kHz AC
DC (0 Hz)
400 Hz AC
50 - 60 Hz AC
Frequencies around 50 - 60 Hz are most efficient at inducing ventricular fibrillation. Higher and lower frequencies require larger currents to achieve the same effect. This is why household current is particularly dangerous..
What is the primary purpose of wearing rubber insulating gloves when working on electrical equipment?
Comfort during work
Prevent moisture on hands
Increase skin resistance and block current flow
Improve grip
Rubber insulating gloves provide high resistance, preventing current from passing through the body. They protect against electric shock when working on energized circuits. They must meet ASTM or IEC voltage ratings..
Above what current level does thermal burn injury become a predominant effect?
1 A
100 mA
10 A
20 mA
Currents on the order of 1 ampere or more cause significant heating of tissues, leading to thermal burns. Lower currents primarily cause neuromuscular effects. Circuit protection devices aim to interrupt before such high currents persist..
What is the commonly accepted safe limit for continuous AC current exposure under occupational settings?
1 mA
5 mA
30 mA
15 mA
Occupational safety guidelines limit continuous exposure to 5 mA for 60 Hz AC to avoid harmful effects. This considers perception and minor muscular effects. Exposures above this require extra precautions..
Which regulatory agency sets workplace electrical safety standards in the United States?
EPA
FDA
NIH
OSHA
The Occupational Safety and Health Administration (OSHA) establishes and enforces workplace electrical safety regulations. Their standards cover safe current exposure, equipment grounding, and protective devices. Compliance is mandatory for U.S. employers..
A current of 0.5 mA at 60 Hz AC is typically described as what sensation?
Let-go phenomenon
Painful shock
Perceptible tingling
No sensation
At 0.5 mA of 60 Hz AC, many individuals notice a mild tingling sensation. This falls below the let-go threshold. It signifies minor sensory nerve stimulation..
What does the term 'microshock' refer to in medical electrical safety?
Microampere currents directly to the heart via an invasive electrode
Currents under 1 mA anywhere on the body
Small sparks from defibrillators
Microampere currents through surface skin
Microshock refers to extremely small currents (often as low as 10 ?A) delivered directly into the heart through invasive devices like catheters. Such currents can induce ventricular fibrillation despite being imperceptible externally. This concept drives strict insulation requirements in critical care..
True or False: The electrical resistance of the human body decreases when the skin is wet.
False
True
Moist or wet skin dramatically lowers body resistance, allowing greater current flow. Wet conditions are considered worst-case in electrical safety. This reduces the threshold for harmful effects..
Which patient group is at greatest risk of microshock effects?
Patients with intracardiac catheters
Pediatric outpatients
Healthy adults without implants
Elderly without cardiac devices
Patients with intracardiac catheters are at highest microshock risk because small currents can directly reach heart tissue. Even microampere-level faults can induce fibrillation. Strict leakage controls are mandated in such environments..
According to IEC 60990, the 50% chance of ventricular fibrillation (Vf) for a 60 Hz sinusoidal AC current occurs at approximately what level?
300 mA
50 mA
100 mA
150 mA
IEC 60990 defines the Vf50 for 60 Hz AC at around 142 mA, often rounded to 150 mA. This is the current at which half of exposed subjects would experience ventricular fibrillation. Standards use it for safe-limit calculations..
Which IEC standard specifically addresses microshock safety in cardiac care equipment?
IEC 60990
IEC 60601-1
IEC 60601-2-2
IEC 62353
IEC 60601-2-2 covers particular requirements for cardiac defibrillators and safeguards against microshock. It sets limits on leakage currents in invasive devices. This helps prevent fibrillation from small faults..
Between monophasic and biphasic defibrillation waveforms, which has a lower ventricular fibrillation threshold at the same peak amplitude?
Biphasic
Monophasic
Depends on the device brand
They are identical
Biphasic waveforms require lower peak currents to achieve defibrillation compared to monophasic. The reversal of polarity increases efficiency and reduces energy requirements. Modern devices use biphasic shocks for safety..
Which frequency of AC current is associated with a higher threshold for ventricular fibrillation compared to 60 Hz?
60 Hz
400 Hz
50 Hz
1 kHz
At 400 Hz, the current required to induce VF is significantly higher than at 60 Hz. The electrical coupling to cardiac tissue decreases with frequency above the power-line range. This is why aircraft systems at 400 Hz are somewhat less arrhythmogenic..
What is the approximate internal impedance of the human thorax at 60 Hz AC, as used in safety calculations?
500 ?
1,000 ?
10,000 ?
100 ?
A typical human thoracic impedance at 60 Hz is around 500 ?. This considers the resistance through chest tissues. Safety models use this to estimate current for VF threshold..
In electrical safety, what does a 'touch voltage' refer to?
Voltage between two feet on the ground
Voltage across two machine parts
Voltage between hand and earth reference
Voltage measured by a multimeter
Touch voltage is the potential difference between a conductive object and ground when touched. It can drive fault current through the body. Standards limit touch voltage to reduce shock risk..
What type of residual current device (RCD) can detect both AC and pulsating DC leakage currents?
Type S
Type A
Type AC
Type B
Type A RCDs detect standard AC and pulsating DC leakages, common when variable-frequency drives are used. Type AC only detects pure AC leakage. Type B detects smooth DC too, making it more advanced..
What is the maximum trip time for a 30 mA RCD at 5 times rated leakage current, per IEC standards?
10 ms
40 ms
100 ms
25 ms
IEC mandates that a 30 mA RCD must trip within 40 ms when subjected to five times its rated leakage current (150 mA). This rapid action minimizes the duration of potentially fatal currents. It protects against electric shock..
According to NFPA 70E, what is the minimum approach distance to exposed 600 V parts without protective equipment?
0.8 m
0.3 m
1.07 m
0.1 m
NFPA 70E establishes an 1.07 m (42 inches) limited approach boundary for 600 V systems without PPE. Entering this zone requires specific protective measures. It reduces arc-flash and shock hazards..
What is the term for the voltage between two points on the ground surface separated by a step distance?
Step voltage
Phase voltage
Touch voltage
Line voltage
Step voltage is the potential difference between two feet spaced apart on the ground surface. It can drive current through the legs during ground faults. Engineers design grounding grids to minimize step voltages..
Which form of current has the highest relative threshold for triggering ventricular fibrillation?
DC
400 Hz AC
50 Hz AC
60 Hz AC
DC current requires larger amplitudes and durations to cause VF compared to AC. The heart is less susceptible to steady DC conduction. AC waveforms, especially at 50-60 Hz, are much more arrhythmogenic..
In measurement of leakage current for medical devices, what method uses a phantom patient circuit?
Insulation resistance test
Two-wattmeter method
Phantom patient test
Direct earth measurement
The phantom patient test simulates a patient connection and measures leakage through the device to the patient. It uses a defined resistive network. This is crucial for microshock and macroshock safety..
What is the significance of the 'WEIDMANN curve' in electrical safety?
Muscle contraction threshold curve
Skin burn threshold curve
Ventricular fibrillation probability vs. current and duration
Arc flash energy curve
The Weidmann curve maps the probability of ventricular fibrillation against current amplitude and exposure time. It is foundational for establishing safe-current limits. Safety standards reference it for risk assessments..
What is the typical duration - current relationship for a 1% chance of ventricular fibrillation at 60 Hz, according to experimental data?
10 mA for 10 seconds
100 mA for 0.1 second
50 mA for 1 second
500 mA for 0.01 second
Studies indicate that around 100 mA for 100 ms yields a 1% probability of VF at 60 Hz. Shorter durations require higher currents. This curve informs circuit protection timing..
Which physiological model best describes the cardiac response to small alternating currents?
Hodgkin - Huxley model
Cable theory
FitzHugh - Nagumo model
Strength - duration curve
The strength - duration curve relates current amplitude to pulse duration for excitation. It applies to cardiac tissue in fibrillation thresholds. It helps predict effects of various waveforms..
What is the effect of adding a series resistor to a DC defibrillation circuit on VF threshold?
Increases current exponentially
No effect
Raises VF threshold
Lowers VF threshold
A series resistor reduces peak current for a given voltage, raising the VF induction threshold. This protects tissue and improves energy control. Manufacturer design uses series resistors in DC circuits for safety..
Which of these factors does NOT significantly affect the ventricular fibrillation threshold?
External ambient noise
Exposure duration
Electrode placement
Current waveform shape
Ambient sound or electromagnetic noise has negligible effect on cardiac fibrillation threshold. The waveform, duration, and electrode placement are primary determinants. Safety testing controls for noise..
In high-frequency electrosurgery devices, which current pathway is optimized to minimize cardiac interference?
Bipolar mode within tissue
Ground pad only
Monopolar mode returning through patient
Radio antenna coupling
Bipolar electrosurgery confines current between two adjacent electrodes, limiting cardiac spread. Monopolar mode can route currents through the patient, increasing risk. Bipolar reduces unintended EMI..
What advanced waveform modification is used to reduce defibrillation energy while maintaining efficacy?
Monophasic truncated sine
High-voltage DC
Unipolar constant current
Biphasic with tilt control
Biphasic waveforms with adjustable tilt (ratio of phases) optimize energy delivery and reduce required energy. Tilt control shapes the waveform to patient impedance. This lowers tissue damage and pain..
Which mathematical law relates the threshold current for excitation to pulse duration in cardiac tissue?
Ohm's law
Kirchhoff's law
Strength - duration law
Weibull law
The strength - duration law quantifies how pulse width and amplitude interact to excite tissue. In cardiac context, it predicts thresholds for defibrillation or stimulation. It is separate from basic circuit laws..
What does the parameter 'chronaxie' represent in electrophysiology?
Time to VF induction
Minimum current at infinite duration
Voltage at which arc flash occurs
Pulse duration at twice the rheobase current
Chronaxie is the duration where double the rheobase current is needed to stimulate tissue. It describes tissue excitability. It is used in strength - duration characterizations..
Which factor decreases the risk of microshock in catheterized patients?
Higher catheter conductivity
Increasing line voltage
Lowering skin resistance
Using ungrounded isolation transformers
Ungrounded isolation transformers remove direct connection to earth, reducing leakage paths to the patient. This protects catheterized patients by minimizing microshock current. It's standard in operating rooms..
What is the FDA's maximum allowable patient leakage current for Type BF medical devices?
100 ?A
50 ?A
10 ?A
500 ?A
FDA mandates a maximum patient leakage current of 100 ?A for BF (Body Floating) classified devices. This reduces microshock and burn hazards. Testing uses a simulated patient circuit..
Which electrode configuration yields a lower defibrillation threshold in biphasic shocks?
Anteroposterior pad placement
Left-right chest placement
Any configuration is equal
Anterolateral pad placement
Anteroposterior paddle placement often yields lower defibrillation thresholds in biphasic shocks due to current path through a larger portion of the ventricles. It improves efficacy compared to purely lateral placements..
In impedance-based defibrillation devices, how is patient impedance typically measured during a shock?
By pre-shock test pulse
Post-shock analysis only
Assuming a fixed 50 ?
Visual estimation
Defibrillators emit a small test pulse before the main shock to measure impedance. This allows energy adjustment for optimal current delivery. It ensures effective defibrillation while minimizing damage..
What is the approximate microshock current threshold for ventricular fibrillation in neonatal catheterized patients?
10 ?A
100 ?A
1 ?A
1 mA
In neonates with intracardiac catheters, around 10 ?A can induce VF due to their small heart mass and catheter proximity. Protocols enforce even tighter leakage limits in neonatal ICUs. This is critical for patient safety..
Which component is critical in a medical-grade isolation transformer to limit patient leakage?
Electrostatic shield between primary and secondary windings
Air gap in core
High-permeability core
Low-turn secondary winding
An electrostatic shield between primary and secondary windings intercepts capacitive leakage currents. It greatly reduces patient leakage currents. This design is mandated for medical isolators..
How does the presence of myocardial ischemia affect the ventricular fibrillation threshold?
Raises the threshold
Lowers the threshold
No change
Varies unpredictably
Ischemic myocardium is more excitable and has reduced threshold for VF induction. Damaged tissue conducts currents differently, making fibrillation easier. Clinical studies support lower VF thresholds in ischemic hearts..
What is the role of the Exponentially Decaying Biphasic waveform tilt in modern defibrillators?
Reduces device size
Mainly cosmetic
Compensates for runoff to match delivered current to patient impedance
Achieves constant energy regardless of impedance
Tilt control shapes the biphasic pulse so that the delivered current adapts to patient impedance. This compensates for exponential voltage decay across the capacitor. It ensures consistent defibrillation efficacy..
In high-voltage cardioversion, what mechanism primarily prevents inadvertent microshock to the operator?
Two-step discharge with polarization reversal
Operator interlock with PPE detection
Grounded primary winding only
Built-in leakage current monitoring with auto-disconnect
Cardioverters continuously monitor leakage and will auto-disconnect or inhibit discharge if leakage exceeds safe limits. This protects operators from microshock risks. Advanced devices integrate this feedback..
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Study Outcomes

  1. Understand current thresholds for cardiac arrest -

    Learn the minimum electrical current levels that can disrupt heart rhythm and lead to cardiac arrest, enhancing your awareness of low current hazards.

  2. Analyze factors influencing electrical injury severity -

    Examine how voltage, current path, duration, and individual physiology affect the risk of cardiac arrest from electrical exposure.

  3. Apply safety protocols to minimize risk -

    Discover industry-standard electrical safety protocols and best practices to prevent accidents when working with live circuits.

  4. Evaluate real-world scenarios involving electrical hazards -

    Assess case studies to identify potential dangers and determine appropriate responses during electrical emergencies.

  5. Recall key principles of electrical safety quiz concepts -

    Solidify your knowledge of the science of electricity quiz topics, including grounding, insulation, and safe equipment handling.

  6. Implement prevention strategies in practical settings -

    Develop actionable steps for maintaining a safe work environment, from using protective gear to establishing emergency procedures.

Cheat Sheet

  1. Ventricular Fibrillation Threshold -

    Even currents as low as 30 mA AC can induce ventricular fibrillation, making this the critical threshold for electrical current cardiac arrest (IEC 60479-1). Studies from the University of California highlight that 50 Hz currents above this level significantly increase risk within 0.2 seconds. Remember "30 and you're in trouble" to recall the rough boundary between harmless and lethal current.

  2. Ohm's Law and Body Resistance -

    Using I = V/R, you can estimate current flow through the body; for example, a 120 V source across 1000 Ω wet skin yields 120 mA - well above the fatal zone. University lab reports note that body impedance varies from 1000 Ω (wet) to 100 000 Ω (dry), reinforcing the importance of accounting for conditions. This physics - medicine crossover is a staple in any science of electricity quiz.

  3. Current Pathway and Heart Exposure -

    The path of electrical current dramatically affects heart involvement: hand-to-hand and hand-to-foot routes cross the thorax, elevating cardiac risk by up to threefold (NIOSH data). Conversely, fingertip-to-fingertip currents often remain superficial, reducing dangerous deep”tissue contact. In electrical safety protocols, always visualize the current's route to gauge low current hazards.

  4. Duration and Frequency Factors -

    IEC research shows that longer exposure (over 500 ms) at even 20 mA can trigger fibrillation, while brief impulses under 100 ms are less likely to be lethal. Additionally, alternating currents at 50 - 60 Hz are more hazardous for causing VF than direct currents of similar amplitude. When tackling the electrical safety quiz, recall that both duration and frequency magnify risk.

  5. Safe Practices and Protective Devices -

    The integration of GFCIs, insulated tools, and proper PPE cuts current levels reaching the body by over 90% according to OSHA guidelines. Lockout”tagout procedures and regular equipment inspections are fundamental in mitigating low current hazards in electrical environments. Embed these measures into your daily routine to prevent electrical current cardiac arrest incidents.

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