Page 164 - WCS - Electrical

work

total
done

P =
Power
total time
p = Nm WORKSHOP CALCULATION & SCIENCE - CITS
Sec

Brake Horse Power = Indicated Horse Power - Losses
1 joule
B.H.P= I.H.P. - Losses = Sec
Mechanical Efficiency
F.s
w
The ratio of Brake Horse Power to Indicated Horse Power is generally termed as mechanical efficiency. Mechanical
=
=
Fxv
=
t
efficiency is generally expressed in percentage.
t
B.H.P
Mechanical Efficiency = 100%×=
I.H.P
Energy
1
- Energy is the capacity to do work or produce heat.
2
- It exists in various forms, including kinetic energy (energy of motion), potential energy (energy of position),
thermal energy, chemical energy, and others.
- The total energy of a system remains constant in the absence of external forces (Law of Conservation of
Energy).
It is equal to power x time.
Hence the unit of energy is the same as the unit of work in all systems.
Uses of Energy

Energy of any form may be transferred to mechanical energy to do a mechanical work. For example, in heat
engines, heat energy is converted into mechanical energy in moving the pistons and mechanical work is done
in driving vehicles, pumps etc. In such a way, electrical energy supplied to a lathe is transformed to mechanical
energy in rotating the spindle and mechanical work is done in turning a job.
Law of conservation of energy

The energy can neither be created nor destroyed.
Total energy possessed by a body remains the same.
This principle allows us to analyze energy transformations in various systems, such as mechanical, electrical, and
thermal systems.

Types of Energy
Depending upon the position of the body or body in motion, mechanical energy possessed by the body may be
potential energy or kinetic energy respectively.

Potential Energy and kinetic Energy
Potential energy is the energy, a body possesses because of its position.
Potential energy = m.g.h. joules
= m.h kg metres
where

m = Mass of body in kilograms
g = Acceleration due to gravity = 9.8 metres/second 2
h = Height in metres
Kinetic energy is the energy a body possesses because of its motion.
Kinetic energy = 1/”2” mv 2

where
m = Mass of body in kilograms
v = Velocity of the body in metres/seconc

151

CITS : WCS - Electrical - Exercise 14