Question

calculate and compare energies of two radiations with wavelength 800 pm and 400 pm each

Answer 1

800pm = 8 A° (angstrom)
400pm = 4 A°
Energy of first radiation = 12400 ÷ 8 = 1550 eV
Energy of second radiation = 12400 ÷ 4 = 3100 eV

Answer 2

First radiation:

The first wavelength is 800pm being h and c are constants.

$E  = \frac {h c} { \lambda}$

Here pm is picometer which is equal to 10^{-12} m.

$= \frac {6.626 \times 10^{-34} J. sec \times 3 \times 10^8 m/sec}  { 800 \times 10^{-12} m}$

$=  0.0248 \times 10^{-14} J$                                                                                                

Second radiation:

The first wavelength is 400pm being h and c are constants.

$E  = \frac {h c} { \lambda}$

$= \frac {6.626 \times 10^{-34} J. sec \times 3 \times 10^8 m/ sec} { 400 \times 10^{-12} m}$

$=  0.0497 \times 10^{-14} J$

h is Planck's Constant (J) and c is the velocity of light (m/s).