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## Electricity

### Electricity

Maybe I am just not getting something or missing something out, I just can't seem to figure out how the answer is d)? Any help/explanation will be much appreciated! Thanks!!

Unit Four
Questions 16-19
The human body may operate as a conductor it completes an electrical circuit. When this occurs
the person may experience an electric shock. The severity of the shock increases as both the
magnitudes of the current and the contact time increase. Different types of tissues have different
conductivities: current passing through electrically excitable tissue like muscle and nerves inflicts
the most pain and damage.
A current between 1 and 10 mA may be perceived as painful, although it is usually harmless to a
healthy individual. However, once current in excess of 10 mA passes through muscle tissue, the
damage inflicted may be more severe, especially if the electrocution is caused by the person
grasping a live wire, which they may not be able to release.
Surprisingly, currents passing through cardiac tissue pose less of a threat if the magnitude of the
current exceeds 1000 mA than if the magnitude were 70 mA. A lower current disrupts the
electrical coupling of the heart, causing irregular contraction, or ventricular fibrillation. A current
over 1 A passing through cardiac tissue is so large that it causes the heart to stop completely;
once the current is removed, the heart usually regains its normal rhythm.
Ohm’s law implies the resistance of the body influences the severity of damage resulting from a
shock. Human tissue has relatively low electrical resistivity since there is an abundance of
dissolved ions in the cells. However, the waterproof outer layer of skin on the body has a high
resistance when dry; approximately 104 Ω. This resistance significantly decreases when the skin
is moistened. The total electrical resistance of the body can be approximated by using the
electrical resistance of the skin.

16 A labourer (with dry skin) accidentally comes into contact with a live wire and
experiences a current of 1 A. The resistance of the wire is 9 Ω. Remembering that
power is the product of current and voltage, how much total energy is dissipated after
45 seconds?
A 15 J.
B 675 J.
C 10 kJ.
D 451 kJ.
cakelover

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### Re: Electricity

Please specify where the question is from. Thanks.
goldstanda3269

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Joined: Wed Aug 25, 2010 10:59 pm