Plotting is not quie correct

I am trying to plot the temeprature curves for emissivity against the wavelength using Planck's Law. The plot I am getting is pretty close, except there is no decrease in emissivity as the wavelength gets very large. I can't tell if it is the way the for loops are running or the equations I typed in. I have attachedmy current code and the graph I am trying to duplicate for clarification. Any help is greatly appreciated. Thanks!

C1 = 3.742*10^8; % First constant W-micron^4/m^2
C2 = 1.4388*10^4; %Second constant microns-K
T = 100:100:6000; %Temperature in Kelvins
lambda = 0.1:0.1:25; %wavelength in microns
lengthT = length(T);
length_L = length(lambda);
E = zeros(lengthT,length_L);
for i = 1:lengthT
    for j = 1:length_L
        term1(i,j) = C2./(lambda(j)*T(i));
    end
    E= C1./((lambda(j)^5)*exp(term1-1));
end
loglog(lambda, E)
ylim([1*10^-1,1*10^9])
xlim([0, 2.5*10^1])

[Walter Roberson]

In order to produce that kind of graph, your expression would need some term that first increased in time and then decreased in time. I am not finding any term in your code that has that property ?

Answer 1

[Torsten]

Maybe

for i = 1:lengthT
    for j = 1:length_L
        term1(i,j) = C2./(lambda(j)*T(i));
        E(i,j)= C1./((lambda(j)^5)*exp(term1(i,j)-1));
    end
    %E= C1./((lambda(j)^5)*exp(term1-1));
end

instead of

for i = 1:lengthT
    for j = 1:length_L
        term1(i,j) = C2./(lambda(j)*T(i));
    end
    E= C1./((lambda(j)^5)*exp(term1-1));
end

?

[Matthew Palermo]

I tried that earlier and got the same result

[Matthew Palermo]

The issue for some reason was splitting up the operation between E and term 1. Consolidating everything into a single step solved the issue

[Image Analyst]

@Matthew Palermo for completeness, could you post your complete, corrected code? It might help other people. 🙂

[Torsten]

@Matthew Palermo

I tried that earlier and got the same result

Strange. I get a similar result as in your graphic.

C1 = 3.742*10^8; % First constant W-micron^4/m^2
C2 = 1.4388*10^4; %Second constant microns-K
T = 100:100:6000; %Temperature in Kelvins
lambda = 0.1:0.1:25; %wavelength in microns
lengthT = length(T);
length_L = length(lambda);
E = zeros(lengthT,length_L);
for i = 1:lengthT
    for j = 1:length_L
        term1(i,j) = C2./(lambda(j)*T(i));
        E(i,j)= C1./((lambda(j)^5)*exp(term1(i,j)-1));
    end
    %E= C1./((lambda(j)^5)*exp(term1-1));
end
loglog(lambda, E)
ylim([1*10^-1,1*10^9])
xlim([0, 2.5*10^1])