Chapter 3:Power and Energy

Problem no:3.3,Page no:24

In [1]:
#cal of Highest voltage drop

#initialization

P=10                       #Power in W

I=0.04                     #Current in A

#calculation

V=P/I

print "V=",int(V),"V"

V= 250 V

Problem no:3.5,Page no:24

In [2]:
#cal of power dissipated as heat

#initialization

R=50                  #Resistance on Ohm

I=2                   #Current in A

#calculation

P=(I**2)*R            #Power Equation

print "P=",P,"W"

P= 200 W

Problem no:3.6,Page no:24

In [3]:
from __future__ import division

#Cal of Resistance

#Initialization

P=3000                    #Power in W

V=240                     #Voltage in V

#calculation

R=(V**2)/P                #Another form of power equation

print "R=",R,"Ohm"

R= 19.2 Ohm

Problem no:3.7,Page no:25

In [4]:
#cal of area of circle

#initialization

r=6                  #Radius in inches

pi=3.14              #Pi constant Value

#calculation

A=pi*r**2            #Area of Circle Euation in square inches

print "A=",int(A),"in^2"

A= 113 in^2

Problem no:3.8,Page no:25

In [5]:
import math

#Cal of Volume of a spherical tank

#Initialization

r=10                        #Radius in m

pi=3.14                     #Pi value constant


#Calculation

V=math.ceil((4*pi*r**3)/3)  #Equation of volume of sphere

print "V=",int(V),"m^3"

V= 4187 m^3

Problem no:3.11,Page no:26

In [6]:
#Cal of Operating voltage

#Initialization

R=18                  #resistance in ohm

P=2                   #Power in W

import math

#calculation

V=math.sqrt(P*R)

print "V=",int(V),"V"

V= 6 V

Problem no:3.12,Page no:26

In [7]:
from __future__ import division

import math

#cal of Maximum current

#initialization

R=50                      #Resistance in Ohm

P=10                      #Power in W

#calculation

I=math.sqrt(P/R)

print "I=",round(I,3),"A"

I= 0.447 A

Problem no:3.13,Page no:27

In [8]:
#cal of radius of wire

#initialization

A=5                      #Area in mm^2

pi=3.14                  #pi constant value

import math

#calculation

r=math.sqrt(A/pi)

print "r=",round(r,2),"mm"

r= 1.26 mm

Problem no:3.15,Page no:28

In [9]:
from __future__ import division

#cal of Energy

#initialization

V=240                      #Voltage in V

I=15                       #Current in A

t=45                       #Time in minutes



#Calculation

P=(I*V)/1000               #Power in kW

t=t/60                     #convert time to hours

W=P*t                      #Work done in kWh

print "W=",round(W,1),"kWh"

W= 2.7 kWh

Problem no:3.16,Page no:28

In [10]:
import math

#cal of Cost per week

#Initialization

P=75                         #Power in W

#Calculation

t=7*24                       #Number of hours in a week

P=75/1000                    #Power in kWh

W=P*t                        #Energy used per week

C=12.6*0.09                  #Cost at $0.09 per kWh

print "Cost per week W =","$",round(C,2)

Cost per week W = $ 1.13