Whats wrong with my for loop?

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Im trying to take in a range on frequencys from a to b from the user and convert that range to wavelength and energy. I want to increment it in 10^2. Ive got the input but I cant get my for loop to work. It keeps saying my energy is 0

What I have tried:

Python

from scipy.constants import Planck

c=299792458

for i in range(a,b,10**5):
    energy=Planck*i
    wavelength=c/i
    
      
    print('{0:>18}'.format(i),'|'\
          '{0:>18.7f}'.format(wavelength), '|', \
          '{0:>18.7f}'.format(energy))

I've also tried this

Python

from scipy.constants import Planck

def energy(x,dx):
    return(Planck*x)
    
def wavelength(x,dx):
    return(c/x)

c=299792458
dx=10**5

for i in range(a,b,dx):
    x=i
    c_wave=wavelength(x,dx)
    c_energy=energy(x,dx)
    
    print('{0:>18}'.format(i),'|'\
          '{0:>18.7f}'.format(c_wave), '|', \
          '{0:>18.7f}'.format(c_energy))

I havent included the getting a and b parts in this but there is a section for the user to input a and b

Posted 15-Mar-20 5:48am

CiaraMc96

Updated 15-Mar-20 22:05pm

Richard MacCutchan

v3

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Richard MacCutchan · Answer 1 · 2020-03-15T06:26:00

Solution 1

I think you have your range values round the wrong way. The correct way is

Python

range(start, end, step)

In your example your step value is 100,000, so it is likely that it will only do a single calculation.

Posted 15-Mar-20 6:26am

Richard MacCutchan

Comments

CiaraMc96 15-Mar-20 14:34pm

The steps meant to be 10^2, I just read it wrong. I got it working to print all the lines for energy but they all still say 0. The range seems to be workinf because it prints all the values between a and b with the step in between and calculates the correct wavelength for each value

Richard MacCutchan 15-Mar-20 18:24pm

Then you need to check each calculation to see what values are being returned. Add some print statements so you can see all the values at each step.

CPallini · Answer 2 · 2020-03-15T22:06:00

The 'problem' is the Plank's constant.
It (and the energy of the single photon) is very, very small (about 6 * 10^-34).
With the format you specified the code shows only zeroes.
This works for me

Python

import scipy.constants as const

for f in range(1,10**5, 10**2):
    energy=const.Planck*f
    wavelength=const.c/f
    print('{0:>18}'.format(f),'|'\
          '{0:>18.7f}'.format(wavelength), '|', \
          '{:>.2E}'.format(energy))

Output (excerpt of the)

('                 1', '| 299792458.0000000', '|', '6.63E-34')
('               101', '|   2968242.1584158', '|', '6.69E-32')
('               201', '|   1491504.7661692', '|', '1.33E-31')
('               301', '|    995988.2325581', '|', '1.99E-31')
('               401', '|    747612.1147132', '|', '2.66E-31')
('               501', '|    598388.1397206', '|', '3.32E-31')
('               601', '|    498822.7254576', '|', '3.98E-31')
('               701', '|    427663.9914408', '|', '4.64E-31')
('               801', '|    374272.7315855', '|', '5.31E-31')
...