Page 163 - WCS - Electrical

WORKSHOP CALCULATION & SCIENCE - CITS

x 1 foot

In M.K.S. system unit of work = 1 joule = 1 Newton x 1
metre
Derived units
C.G.S. system 1 Gm Wt x 1 cm = 981 ergs.
F.P.S. system 1 ft LB = 981 foot poundal

M.K.S. system 1 kgf metre = 981 joule.
Power
- Power is the rate at which work is done or energy is transferred.
It is the work done in unit time.

work
total

done
- Mathematically, Power=Time/Work P = total work done
Power

total

time
Power P = total work done Power P = total time

total
done
work

=
Power P= P Power total time time
total
Nm

p =
p = Nm
Sec

P= Nm Sec
p =
Sec Nm
p =
Sec
1
joule

The S.I units of power = 1Nm/sec = = joule
1
Sec
1 joule = Sec
=
1
Sec joule
=
F.s
w
Sec w = F.s = Fxv
=
Which is = 1 watt.power in watts=
w = F.s = F.s = t t= t t = Fxv
Fxv
=
w
t
t
Fxv
=
=
=
Which is equal to 1 watt. Power in watts = w/t=F.s/t = F x V
B.H.P
t
t
=
100%
×
=
I.H.P 100%×
- Power is measured in watts (W) and represents the amount of energy transferred per unit time.
B.H.P B.H.P
I.H.P
= × 100%
B.H.P
I.H.P
- It is also related to force and velocity: Power=Force x Velocity.
100%
×
=
1
I.H.P
1
The absolute unit of power is watt. One watt is that power which is required to perform 1 joule of work in 1 second.
2
1
1 watt = 1 joule/second = 10 7ergs /second
2
2 1
1 kilowatt =1000 watts.
2
The practical unit of power is Horse Power (H.P.). One horse power (H.P.) is the amount of work, a standard horse
can do in one second. This value in metric system is 75 kg metres per second and in British system is 550 foot
pounds/ second.
1 H.P. (Metric) = 75 kg metres per second = 735.5 watts
1 H.P. (British) = 550 foot pounds/second = 746 watts
Horse Power of Engines
The following terms are generally used in case of engines:
Indicated Horse Power (I.H.P.)
The actual power generated in the engine cylinder is called as the Indicated Horse Power (I.H.P.)
Brake Horse Power (B.H.P.)
It has been observed that all the power generated by the engine cylinder is not available for useful work. This
happens because a part of it is always utilized in overcoming the internal friction of the moving parts of the engine.
The net output of the engine is termed as Brake Horse Power (B.H.P.)
150
CITS : WCS - Electrical - Exercise 14