# Chapter 4: Work Power and Energy¶

### Example 4.1: Page 61¶

In [1]:
from __future__ import division
import math

#given  data  :
I=11;#  current  in  A
V1=55;#  voltage  in  V
V2=220;#  voltage  in  V

#calculations
V=V2-V1;
R=V/I;
P=I**2*R;

#Results
print  "(a)resistance,R  = ", R," ohm"
print  "(b)power  lost,P = ",P," W"

(a)resistance,R  =  15.0  ohm
(b)power  lost,P =  1815.0  W


### Example 4.2: Page 61¶

In [2]:
from __future__ import division
import math

#given  data  :
V=300;#  voltage  in  volts
W=360;#  power  lost  in  one  coil  in  watt
I=6;  #  current  in  A

#calculations:
R1=V/I;
R=V**2/W;
a=(1/R1)-(1/R);
r2=1/a;

#Results
print  "resistance  of  360W  coil1,R= ",R,"ohm and \n resistance  of  second  coil2,r2=",r2,"ohm"

resistance  of  360W  coil1,R=  250.0 ohm and
resistance  of  second  coil2,r2= 62.5 ohm


### Example 4.3: Page 61¶

In [3]:
from __future__ import division
import math

#given  data  :
W1=100#  in  watt
E=110#  in  volts
W2=60#  in  watt

#calculations:
I1=W1/E#  current  taken  by  100  w  lamp
I2=W2/E#  current  taken  by  60W  lamp
I=I1-I2;
R=E/I;

#Results
print  "resistance,R =", R," ohm"

resistance,R = 302.5  ohm


### Example 4.4: Page 62¶

In [4]:
from __future__ import division
import math

#given  data  :
w=100;#  in  watt
V=220;#  voltage  in  volts

#calculations:
R1=V**2/w;
Rp=R1/2;#  total  resistance  of  the  circuit
Ip=V/Rp;
Wp=Ip**2*Rp;
R2=V**2/w;
Rs=R1+R2;#  total  resistance  of  the  circuit
Is=V/Rs;
Ws=Is**2*Rs;

#Results
print  "(a)power  in  case  of  parallel,W =  ",Wp,"watts"
print  "(b)power  in  case  of  series, W  =  ",Ws," Watts"

(a)power  in  case  of  parallel,W =   200.0 watts
(b)power  in  case  of  series, W  =   50.0  Watts


### Example 4.5: Page 63¶

In [3]:
from __future__ import division
import math

#given  data  :
V = 220; #voltage
l=300;#  number  of  lamps
w1=60;#  in  watt
w2=40;#  in  watt
f=100;#  number  of  fan

# Calculations:
W1=w1*l;#  wattage  required  for  300  lamps,  60  watt  each
W2=w2*f#  wattage  required  for  100  fans,  40  watt  each
W=(W1+W2)*10**-3;
I=(W*1000)/V;

#Results
print "(a)total  load,W  =  ",W," kW"
print "(b)current,I =  ",I,"A"

(a)total  load,W  =   22.0  kW
(b)current,I =   100.0 A


### Example 4.6: Page 63¶

In [4]:
from __future__ import division
import math

#given and Calculations:
nl=12#no.  of  lamps
wl=100#wattage  of  lamps
hl=6  #each  lamps  work  6  hours  a  days
nf=6  #no.  of  fans
wf=60#wattage  of  fans
hf=5  #each  fans  work  5  hours  a  days
nc=2  #no.  of  electric  cookers
wc=1500#wattage  of  electric  cookers
hc=4  #each  electric  cookers  work  4  hours  a  days
ng=2  #no.  of  gysers
wg=1000#wattage  of  each  gyser
hg=3  #each  gyser  works  3  hours  a  day
Ccg=40#IN  PAISA
Ccg1=35#IN  PAISA

# Calculations:
w12=wl*nl*hl#wattage  of  12  lamps  in  Wh
w6=wf*nf*hf#wattage  of  12  fans  in  Wh
w2=wc*nc*hc#wattage  of  2  electric  cookers  in  Wh
w21=wg*hg*ng#total  wattage  of  gysers  in  Wh
tcg=(w12+w6)*10**-3#TOTAL  WATTAGE  OF  LAMPS  AND  FANS
Ecg=  (tcg*Ccg*30)/100#TOTAL  ENERGY  CHARGES  @40  PAISA  PER  UNIT
tcg1=(w2+w21)*10**-3#TOTAL  WATTAGE  OF  COOKERS  AND  GYSERS
Ecg1=  (tcg1*Ccg1*30)/100#TOTAL  ENERGY  CHARGES  @35  PAISA  PER  UNIT
tc=Ecg+Ecg1#  IN  RUPPES

#Results
print  "total  cost  of  electric  charge  @40  paisa  per  unit  in  rupees",Ecg
print  "total  cost  of  electric  charge  @35  paisa  per  unit  in  rupees",Ecg1
print  "total  charge  for  ligh  and  power  in  rupees",tc

total  cost  of  electric  charge  @40  paisa  per  unit  in  rupees 108.0
total  cost  of  electric  charge  @35  paisa  per  unit  in  rupees 189.0
total  charge  for  ligh  and  power  in  rupees 297.0


### Example 4.7: Page 63¶

In [5]:
from __future__ import division
import math

#given and Calculations
V = 250;#volts
r = 0.03; #in ohms
I = 20; #in Amps
nl=400#no.  of  lamps
wl=100#wattage  of  lamps
nf=100#no.  of  fans
wf=40#wattage  of  fans
nc=200#no.  of  wall  scokets
wc=60#wattage  of  wall  scckets
h=5    #  hours

# Calculations:
w400=wl*nl#wattage  of  400  lamps  in  W
w6=wf*nf#wattage  of  100  fans  in  W
w2=wc*nc#wattage  of  200  wall  sockets  in  Wh
tc=  (w400+w6+w2)/1000#total  consumption  in  kW
Mo=  ((50*80*746)/(100*1000))#MOTOR  AT  80%  LOAD  IN  Kw
It = tl*1000/V
Vc=It*r#voltage  drop  in  the  cable
Vs=Vc+V#voltage  at  the  sending  end  of  the  feeder  in  volts
Pw=It**2*r#power  wasted  in  kW
te=Ml*2 + ll#TOTAL  ENERGY  COSNUMED  PER  DAY
Nu=te*6#NO.  OF  UNITS
Ec=(Nu*30)/100#  ENERGY  CHARGE  @30  PAISA  PER  UNIT
eCM=Ec+2+34.80#TOTAL  CHARGE  AFTER  TAX  AND  RENT  IN  RUPEES.
TEP=hlh+Moh#total  energy  per  day
tepl=TEP*6#total  energy  in  6  days
tepc=(tepl*35)/100#  energy  charges  @35  paisa  per  unit  in  rupees
tepcl=tepc+50+78.96#total  charges  in  rupess

GTb = eCM + tepcl

#Results
print  "(a)total  consumption  of  factory is ", tl,"kW"
print  "(b)total  current  taken  buy  the  factory",It," Amp"
print  "(c)voltage  at  the  sending  end  of  the  feeder  is",round(Vs,1),"Volts"
print  "(d)power  wasted  is",round(Pw/1000,2),"kW"
print  "(e)total  lightning  charges-  including  meter  rent  and  electricy  tax  is,(Rs)=",round(eCM,2)
print  "total  power  charges  including  meter  rent  and  electricy  tax  is,(Rs)=",round(tepcl,2)
print  "grand  total  of  bills  is,(Rs)=",round(GTb,2)

(a)total  consumption  of  factory is  140.84 kW
(b)total  current  taken  buy  the  factory 563.36  Amp
(c)voltage  at  the  sending  end  of  the  feeder  is 266.9 Volts
(d)power  wasted  is 9.52 kW
(e)total  lightning  charges-  including  meter  rent  and  electricy  tax  is,(Rs)= 558.8
total  power  charges  including  meter  rent  and  electricy  tax  is,(Rs)= 1050.27
grand  total  of  bills  is,(Rs)= 1609.07


### Example 4.8: Page 64¶

In [8]:
from __future__ import division
import math

#given  data  :
V=250;#  voltage  in  volts
L=5*746;#  1  hp=746  watt
eta=80#  eficiency  of  motor  in  %

# Calculations:
Input=(L*100)/80;
I=Input/V;

#Results
print  "cureent,I(A)  =  ", I

cureent,I(A)  =   18.65


### Example 4.9: Page 64¶

In [9]:
from __future__ import division
import math

#given:
p=30  #horse  power  of  motor
r=24  #  rupees  per  kWh
ec=35#paisa  per  unit
t=8    #  in  hours
d=25  #  total  days
ne=96#efficiency  of  motor  in  percentage

#calculations:
mo=(n*p)/100#output  of  motor  at  80%  of  load
mi=(mo*100*746)/(ne)#input  of  motor  in  watts
ecm=mi*10**-3*t*d#energy  consumed  in  a  month
ecu=(ecm*35)/100#energy  charges
mid=(30*100*746)/(ne*1000)#input  of  motor  in  kW  at  demanded
ecud=(mid*24)#  demanded  connection  in  rupees
ta=ecu+ecud#total  bill  in  rupees

#Results
print  "total  bill  in  rupees  is",ta

total  bill  in  rupees  is 1865.0


### Example 4.10: Page 65¶

In [10]:
from __future__ import division
import math

#given:
V=400#three  phase  voltage
lp=50#no.  of  light  points
lw=60#wattage  of  light  points
fp=20#no.  of  fan  points
fw=100#wattage  of  fan  points
wpp=10#no.  of  wall  plug  points
wppw=60#wattage  of  wall  plug  points
bp=5  #no.  of  bell  points
bpw=40#wattage  of  bell  points
ppp=8#power  plug  points
pppw=500#wattage  of  power  plug  points

#calculations:
lpw=lp*lw#wattage  of  50  lamps
fpw=fp*fw#wattage  of  20  fans
wpppw=wpp*wppw#wattage  of  wall  plug  points
bpww=bp*bpw#wattage  of  bell  points
tl=lpw+fpw+wpppw+bpww#total  wattage
ppppw=ppp*pppw#wattage  of  power  plug  points
tw=tl+ppppw#total  wattage

#Results
print  "total  wattage  of  lightning  load  is  in  watts = ", tl
print  "total  load  current  in  amperes = ",ttl

total  wattage  of  lightning  load  is  in  watts =  5800
total  load  current  in  amperes =  24.5


### Example 4.11: Page 66¶

In [6]:
from __future__ import division
import math

#given  data  and calculations:
h=30;#  in  m
Fl=10#  friction  loss  in  %
eta=90;#  eficiency  of  pump
w=1000;#  water  weight  in  kg
flow_rate=243;#  in  per  hour

# Calculations:
Hl=(Fl/100)*h;
total_H=h+Hl;
W_done=(flow_rate*w*total_H)/60;#  in  kg-m/min
output=W_done/4500;#output  of  pump  in  hp
In=(output*100)/eta;
O=In;

#Results
print  "output  of  the  motor,O(hp)  =  ",O

output  of  the  motor,O(hp)  =   33.0


### Example 4.12: Page 66¶

In [12]:
from __future__ import division
import math

#given data:
h=135#height  in  meters
c=0.5#cge  weight  in  tonnes
b=3    #balance  weight  in  tonnes
td=90#time  in  seconds
onet=1000#  in  kg
onehp=746#watt

#calculations:
wl=l+c-b#weight  lifted  during  upward  journey  in  tonnes
wld=b-c#weight  lifted  during  downward  journey  in  tonnes
wdu=(wl*10**3*h*60)/td#work  done  by  the  lift  per  minute  during  upward  journey
wdd=(wld*10**3*h*60)/td#work  done  by  the  lift  per  minute  during  downward  journey
mou=wdu/4500#  in  hp
miu=(mou*100*746)/(n*1000)#  input  of  motor  in  kW
mod=wdd/4500#  in  hp
mid=(mod*100*746)/(n*1000)#  input  of  motor  in  kW
tc=miu+mid#total  energy  consumption  in  kW
Eh=tc*10#total  energy  consuption  per  hour
rate=40#rate  in  paisa
ce=Eh*(rate/100)#cost  of  energy  in  rupees

#Results
print  "(a1)BHP  of  the  motor  in  upward  journey  in  hp",mou
print  "(a2)BHP  of  the  motor  in  downward  journey  in  hp",mod
print  "(b)cost  of  energy  in  rupees  is" ,ce

(a1)BHP  of  the  motor  in  upward  journey  in  hp 100.0
(a2)BHP  of  the  motor  in  downward  journey  in  hp 50.0
(b)cost  of  energy  in  rupees  is 559.5