# Chapter 12 : Radiation¶

## Example 12.1 pageno : 445¶

In [2]:
# Variables
t1 = 300;			#temperature of the surroundings in K
t2 = 900;			#temperature of the hot body p in K
t3 = 500;			#temperature of the hot body q in K
a = 5.67*10**-8;			#stefan boltzmann consmath.tant in W/m**2.K**4

# Calculations
q1 = a*(t2**4-t1**4);			#heat lost from hot body p in w/m**2
q2 = a*(t3**4-t1**4);			#heat lost from hot body q in w/m**2
q = q1/q2;			#ratio of heat lost from two subsmath.tances

# Result
print 'ratio of heat lost from two substances is %3.1f/1'%(q)

ratio of heat lost from two substances is 11.9/1


## Example 12.2 pageno : 445¶

In [4]:
# Variables
t1 = 573;			#temperature of the hot side in K
t2 = 273;			#temperature of the coll side in K
m = 82;			#mass of the black body in gm
cp = 0.1;			#specific heat of the black body kj/kg.K
dt = 0.35;			#ice melting at a rate of temperature in deg.C/sec
a = 8;			#area of black body in sq.cm

# Calculations
s = m*cp*dt/(a*(t1**4-t2**4));			#boltzmann constant in cal/sq.cm/sec/deg**4

# Result
print 'boltzmann consmath.tant is %.2e cal/sq.cm/sec/deg**4'%(s)

boltzmann consmath.tant is 3.51e-12 cal/sq.cm/sec/deg**4


## Example 12.3 pageno : 445¶

In [5]:
# Variables
r1 = 60.;			#distance of first black body in cm
r2 = 30.;			#distance of second black body in cm
t1 = 873.;			#temperature of first black body in K
t2 = 573.;			#temperature of the second black body in K

# Calculations
i = (t2**4/t1**4)*(r1**2/r2**2);			#ratio of intensity of radition

# Result
print 'ratio of intensity of radition is %3.2f'%(i)

ratio of intensity of radition is 0.74


## Example 12.4 pageno : 445¶

In [7]:
# Variables
t1 = 1373;			#temperature of the sphere in K
t2 = 283;			#temperature of the black body in K
r = 4.17*10**5;			#rate of heat radiate in ergs/sq.cm/sec
a = 4*3.14*(6**2);			#surface area of the sphere in sq.cm

tr = r*a*(t1**4/t2**4)*(2.39005736*10**(-8));			#total heat radiated in cal/sec

# Result
print 'total heat radiated is %3.1f cal/sec'%(tr)

total heat radiated is 2496.6 cal/sec


## Example 12.5 pageno : 446¶

In [8]:
# Variables
h = 2*3.14*100;			#heat received by the lens per min in  cal
m = 25.;			#mass of the ice in gm
l = 80;			#latent heat of ice in cal/gm

# Calculations
t = m*l/h;			#time for which the sun rays falls in min

# Result
print 'time for which the sun rays falls is %3.3f min'%(t)

time for which the sun rays falls is 3.185 min


## Example 12.6 page no : 446¶

In [10]:
# Variables
d = 0.35;			#diameter of the mirror in m
t = 5;			#time in min
T = 16;			#temperature of water found to be in deg.C
m = 60;			#mass of water in gm
mc = 30;			#mass of calorimeter in gm
cp = 0.1;			#specific heat of copper in cal/gm/deg.C

# Calculations
q = (m+cp*mc)*T*4/(5*3.14*d**2);			#amount of heat received by earth in cal

# Result
print 'amount of heat received by earth is %3.f cal'%(q)

amount of heat received by earth is 2096 cal


## Example 12.7 pageno : 446¶

In [16]:
# Variables
r1 = 5.;			#radius of first sphere in cm
r2 = 10.;			#radius of second sphere in cm
t1 = 700.;			#temperature of the first sphere in K
t2 = 500.;			#temperature of the second sphere in K
t = 300.;			#temperature of the enclousure in K

# Calculations1
dc = (r2/r1)*(t1**4-t**4)/(t2**4-t**4);			#ratio of c1/c2
r = r1**3*dc/r2**3;			#rate of heat loss

# Result
print 'rate of loss of heat is %3.3f'%(r)

rate of loss of heat is 1.066


## Example 12.8 pageno : 447¶

In [19]:
# Variables
t1 = 600.;			#temperature of the black body in K
t0 = 300.;			#temperature of the surroundings in K
d = 6.;			#deflections in galvanometer
d1 = 400.;			#deflection in divisions

# Calculations
dt = (d1/d)*(t1**4-t0**4);			#change of temperature
t2 = (dt+t0**4)**(1./4);			#end temperature in K

# Result
print 'end temperature of the temperature is %3.2f K'%(t2)
print "Note : answer in book in incorrect. Please calculate manually."

end temperature of the temperature is 1687.45 K
Note : answer in book in incorrect. Please calculate manually.


## Example 12.9 pageno : 447¶

In [21]:
# Variables
n = 17000;			#luminosity of star compared to sun
t = 6000;			#temperature of the sun in K

# Calculations
t1 = (n*t**4)**(1./4);			#temperature of the star in K

# Result
print 'the temperature of the star is %3.f K'%(round(t1,-1))

the temperature of the star is 68510 K