Electric currents in the body A person accidentally touches a 120-V electric line with one hand

Electric currents in the body A person accidentally touches...

Electric currents in the body A person accidentally touches a $120-\mathrm{V}$ electric line with one hand while touching a ground wire with the other hand. Determine the current through the body when the hands are dry $(100,000-\Omega$ resistance) and when wet $(5000-\Omega$ resistance). If the current exceeds about $10 \mathrm{mA}$, muscular contractions may prevent the person from releasing the wires- a dangerous situation. Is the person in danger with dry hands? With wet hands? Explain.

Electric currents in the body A person accidentally touches a $120-\mathrm{V}$ electric line with one hand
while touching a ground wire with the other hand. Determine the current through the body when the hands are dry $(100,000-\Omega$ resistance) and when wet $(5000-\Omega$ resistance). If the current exceeds about $10 \mathrm{mA}$, muscular contractions may prevent the person from releasing the wires- a dangerous situation. Is the person in danger with dry hands? With wet hands? Explain.

Key Concepts

Threshold Current for Muscular Contraction

There is a critical threshold of electrical current, typically around 10 mA, at which involuntary muscular contractions occur. When current above this threshold passes through the body, it can cause severe and potentially dangerous reactions, such as the inability to let go of an electrified object. This threshold is vital in determining whether a given electrical exposure is unsafe.

Human Body and Electrical Shock

The human body can conduct electricity, and the amount of current that flows through it depends on the voltage applied and the body’s resistance. Different levels of current can affect the body in various ways, from a mild sensation to severe harm, including muscular contractions and cardiac disturbances. This concept is important in evaluating the risk associated with electrical exposure.

Electrical Resistance

Electrical resistance is a measure of how much an object opposes the flow of electric current. The human body has a certain resistance that varies based on conditions such as skin moisture; dry skin has a higher resistance compared to wet skin. Understanding the concept of resistance is essential in assessing how much current will flow through the body when exposed to an electrical source.

Ohm's Law

Ohm's Law is a fundamental principle in electrical engineering that states the relationship between voltage (V), current (I), and resistance (R) in a circuit, given by I = V/R. It is crucial for calculating the current that flows through a conductor when a specific voltage is applied across a resistance. In the context of this question, it is used to determine the current passing through the body by dividing the applied voltage by the body’s resistance.

Transcript

00:03 Just a side note, we're assuming that this is a 120 volt dc system, but if it was a 120 volt ac system, then impedance is applicable not resistance.

00:16 But since this is a chapter on dc circuits, we'll assume we're dealing with a 120 volt dc line and let's say something that's used for industrial purposes, perhaps 120 volt ac rectified to 120 volt.

00:33 D .c.

00:35 Could be for systems like trolleys in some countries.

00:39 So assume somebody grabs both lines, positive and negative, it's a dipole ground, and dry hands.

00:50 It's measured at 100 ,000 oms of resistance when the current travels through the body and 5 ,000 oms through the body with wet hands.

01:02 So if we just divide the total voltage input into the resistance, we can calculate the current distribution through the body.

01:12 So the dry hands would distribute 1 .2 milanps through the individual's body and 24 milliamps through the body when wet, wet hands 24 milliamps, dry hands 1 .2 milliamps.

01:30 So the wet hands are actually more actually a danger due to the fact that greater than 10 milliams, the body skeletal muscle system will perhaps most likely not have the ability to relax the skeletal muscles due to the electrical limitations of the nervous system.

01:56 So we do know that actin in myosin are what caused the muscles in the body to contract and relax.

02:07 This is an electrolytic reaction, and the scientific standard indicates that equal to or greater than 10 milan amps.

02:18 If someone grabs such a line, the hands would not be able to relax or let go.

02:25 And so this is a huge risk for not so much electrocution, but severe burns, including burning the flesh off the hands with something like this happening...

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