Page 102 - CITS - WCS - Mechanical

WORKSHOP SCIENCE - CITS

• Entertainment.

• Healthcare.
• Engineering.
• Transport and Communication.
• Outdoors.
• Household.

• Commercial.
• Office.
It is used for heating, lighting, cooling, refrigeration, household appliance, transportation, electronic appliances,
industrial machinery, etc. The usage of electricity is not limited to a certain point it has unlimited uses in the
modern era of today.
Difference between ac and dc

In alternating current (AC), the voltage periodically changes from positive to negative and from negative to positive,
and the direction of the current also periodically changes accordingly. DC is stands for direct current means it has
a fixed amplitude and no frequency. It has polarity of + and -. Current produced by generators or Turbine are AC
currents and the current we get from our HOME power sockets are AC current. Mostly Electrical appliances like
FAN, Bulb, AC, Motors are works on AC current.
Primary DC is generated by batteries and electrochemical of photovoltaic cells. Power loss during transmission
is more in direct current as compared to alternating current. In direct current, the voltage is always constant, and
the electricity flows in a certain direction. AC electricity is more dangerous to work with due to these reasons:
The human body has a higher impedance to DC currents than AC; humans can withstand higher voltages of
DC electricity than AC. AC is less expensive and easy to generate than DC. AC can be transmitted across long
distances without much energy loss, unlike DC.
Safety devices
An electric fuse is a safety device, which is used to limit the current in an electric circuit. The use of fuse safeguards
the circuit and appliances connected in that circuit from being damaged. An alloy of lead and tin is used as a
material of fuse because it has low melting point and high resistivity. The ground-fault circuit interrupter, or GFCI,
is designed to shut-off electric power if a ground fault is detected, protecting the user from a potential electrical
shock. The GFCI is particularly useful near sinks and wet locations.
5 tips for electrical safety

1 Avoid contact with power lines.
2 Ground electrical equipment.
3 Take care with power tools.
4 Wear protective clothing.
5 Stay on top of housekeeping
MCBs and MCCBs are circuit breakers with varying current ratings, suited for different load capacities. RCB,
RCD, RCCB, and RCBO, on the other hand, focus on protecting against residual currents and electric shock.
MCB (Miniature Circuit Breaker) is for basic protection device to limit the current and fault in a circuit whereas
ELCB (Earth Leakage Circuit Breaker) is advanced one which responds only when the circuit leaks current to
earth. RCCBs are designed to detect and trip when a current imbalance is detected, which can indicate an electric
shock.
Rubber insulting gloves are the preferred choice as they are generally designed to protect against electrical
hazards.

Difference between conductors and semiconductors and Resistors
• Conductors are materials that readily allow the flow of electric current. They typically have low resistance
and high conductivity. The properties of conductors can be attributed to the following factor. Conductors have
loosely bound valence electrons that are free to move within the material. This electron mobility enables
efficient electric current flow.

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CITS : WCS - Mechanical - Exercise 9