Page 391 - IGC BOOK

Resistance

Just as friction opposes motion around you, there is an electrical quantity that opposes or resists
the flow of electric current. This amount of resistance in an electrical circuit relative to the
movement of electrons is measured in ohms (Ω).

OHM’S LAW

Conductors are elements that have atoms with electrons
that will pass through them easily. Example of good
conductor is copper. Certain materials do not allow current
to pass through them are called as insulators. Water is a
good conductor of electricity, hence electrical equipment in
wet condition can be more dangerous.

When there is a flow of current in a circuit it is referred as
“Live”, when the circuit is isolated it is referred as “Dead”. Ohm's Law

Static electricity refers to the electric charge of an object and the related electrostatic discharge
when two objects are brought together that are not at equilibrium. When the static electricity is
discharged to earth it is felt as shock, static electricity is unlikely to cause hurt, but it is potential to
ignite flammable dust or vapour in the atmosphere.

Hazards and Risks of Electricity

The main hazards associated with electricity

• Electric Shock
• Burns
• Fire and explosion
• Arcing
• Secondary effects

Electric Shock

When the human body come into contact with live current, the current flow through the body from
the point to contact to the earth to complete the circuit. This causes convulsion of the human body
which is called electric shock. The sensation of electric shock can be extremely painful. The passage
of electric current may cause muscular contractions, respiratory failure, fibrillation of the heart,
cardiac arrest or injury from internal burns. Any of these can be fatal.

Current flowing thorough the body Effect
0.001 Ampere (1 mA) Mild tingling sensation that can be felt
0.010 Ampere (10 mA) Start to lose muscular control
0.030 Ampere (30 mA) Breathing difficulty, muscular paralysis
0.100 Ampere (100 mA) Fatal if current lasts more than a second
0.200 Ampere (200 mA) Severe burns, both internal and external and fatal

ENSIGN | Unit IG2 – Element 11 – Electricity 2