High School Physics

Electric current & shock

Last updated on May 14th, 2022 at 02:04 pm

This post is a compilation of a set questions with answers related to electric current flow and electric shock.

What levels of current are dangerous?

  • Approximately 1 mA (0.001 A) is enough to produce a tingling sensation.
  • 10 mA is painful.
  • 12-20 mA is enough to paralyze muscles, making it impossible to let go.
  • 60-100 mA causes ventricular fibrillation of the heart. That means, the heart is beating in such a way that it cannot pump blood through the circulatory system.
  • Greater than 200 mA causes the heart to clamp down and stop beating.

How much resistance do our bodies have to electrical current?

The human body, on average, has an electrical resistance between 50,000 and 150,000 ohms.

Most of the resistance of our body is across the skin. But this resistance across the skin can drop as described below:

  • If the skin is wet the resistance drops to about 1,000 ohms.
  • If the skin is broken, then resistance across organs in the body is on the order of a few hundred ohms. In this condition, 10 volts is sufficient to cause serious, if not fatal damage.

Do electric eels really use electric fields to capture their prey?

Electric eels do really use electrical pulses to stun and even kill their prey.

These eels have special nerve endings bundled together in their tails that can produce 30 volts in small electric eels to 600 volts in larger eels. Besides using the electrical shocks for hunting, the eels produce a constant electrical field for use in navigation and self-defense.

Most people do not have to worry about encountering electric eels, however. This variety of eel is native only to the rivers of South America.

Why don’t birds or squirrels on power lines get electrocuted?

In order to get electrocuted on a bare wire, a bird would have to be in contact with objects that had two different voltages. When the animals are sitting on a single wire, then the difference in voltage along the wire over the distance between the animal’s feet is very small. Hence, the current flow is very less. In these situations, birds or squirrels on power lines don’t get electrocuted.

The animal would be in danger only if it makes contact with both a high-voltage wire and the ground or a wire connected to the ground (low voltage). This will cause a huge potential difference and there could be a large current through its body.

Does voltage shock you?

Signs around power plants and breaker boxes often state, “CAUTION: High Voltage Area.”

It is not the voltage that can hurt us; it is the electrical current that flows through our body that can produce serious and sometimes fatal consequences.

The Van de Graaff generator creates hundreds of thousands of volts but produces such a low amount of current that the sparks it emits only cause muscles to tingle.

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