Answer:
4.63 p.m.
Explanation:
The problem given here can be solved by the Compton effect which is expressed as
![\lambda^{'}-\lambda=\frac{h}{m_e c}(1-cos\theta)](https://tex.z-dn.net/?f=%5Clambda%5E%7B%27%7D-%5Clambda%3D%5Cfrac%7Bh%7D%7Bm_e%20c%7D%281-cos%5Ctheta%29)
here,
is the initial photon wavelength,
is the scattered photon wavelength, h is he Planck's constant,
is the free electron mass, c is the velocity of light,
is the angle of scattering.
Given that, the scattering angle is, ![\theta=157^{\circ}](https://tex.z-dn.net/?f=%5Ctheta%3D157%5E%7B%5Ccirc%7D)
Putting the respective values, we get
![\lambda^{'}-\lambda=\frac{6.626\times 10^{-34} }{9.11\times 10^{-31}\times 3\times 10^{8} } (1-cos157^\circ ) m\\\lambda^{'}-\lambda=2.42\times 10^{-12} (1-cos157^\circ ) m\\\lambda^{'}-\lambda=2.42(1-cos157^\circ ) p.m.](https://tex.z-dn.net/?f=%5Clambda%5E%7B%27%7D-%5Clambda%3D%5Cfrac%7B6.626%5Ctimes%2010%5E%7B-34%7D%20%7D%7B9.11%5Ctimes%2010%5E%7B-31%7D%5Ctimes%203%5Ctimes%2010%5E%7B8%7D%20%20%7D%20%281-cos157%5E%5Ccirc%20%29%20m%5C%5C%5Clambda%5E%7B%27%7D-%5Clambda%3D2.42%5Ctimes%2010%5E%7B-12%7D%20%281-cos157%5E%5Ccirc%20%29%20m%5C%5C%5Clambda%5E%7B%27%7D-%5Clambda%3D2.42%281-cos157%5E%5Ccirc%20%29%20p.m.)
Therfore,
![\lambda^{'}-\lambda=4.64 p.m.](https://tex.z-dn.net/?f=%5Clambda%5E%7B%27%7D-%5Clambda%3D4.64%20p.m.)
Here, the photon's incident wavelength is ![\lamda=7.33pm](https://tex.z-dn.net/?f=%5Clamda%3D7.33pm)
So,
![\lambda^{'}=7.33+4.64=11.97 p.m](https://tex.z-dn.net/?f=%5Clambda%5E%7B%27%7D%3D7.33%2B4.64%3D11.97%20p.m)
From the conservation of momentum,
![\vec{P_\lambda}=\vec{P_{\lambda^{'}}}+\vec{P_e}](https://tex.z-dn.net/?f=%5Cvec%7BP_%5Clambda%7D%3D%5Cvec%7BP_%7B%5Clambda%5E%7B%27%7D%7D%7D%2B%5Cvec%7BP_e%7D)
here,
is the initial photon momentum,
is the final photon momentum and
is the scattered electron momentum.
Expanding the vector sum, we get
![P^2_{e}=P^2_{\lambda}+P^2_{\lambda^{'}}-2P_\lambda P_{\lambda^{'}}cos\theta](https://tex.z-dn.net/?f=P%5E2_%7Be%7D%3DP%5E2_%7B%5Clambda%7D%2BP%5E2_%7B%5Clambda%5E%7B%27%7D%7D-2P_%5Clambda%20P_%7B%5Clambda%5E%7B%27%7D%7Dcos%5Ctheta)
Now expressing the momentum in terms of De-Broglie wavelength
and putting it in the above equation we get,
![\lambda_{e}=\frac{\lambda \lambda^{'}}{\sqrt{\lambda^{2}+\lambda^{2}_{'}-2\lambda \lambda^{'} cos\theta}}](https://tex.z-dn.net/?f=%5Clambda_%7Be%7D%3D%5Cfrac%7B%5Clambda%20%5Clambda%5E%7B%27%7D%7D%7B%5Csqrt%7B%5Clambda%5E%7B2%7D%2B%5Clambda%5E%7B2%7D_%7B%27%7D-2%5Clambda%20%5Clambda%5E%7B%27%7D%20cos%5Ctheta%7D%7D)
Therfore,
![\lambda_{e}=\frac{7.33\times 11.97}{\sqrt{7.33^{2}+11.97^{2}-2\times 7.33\times 11.97\times cos157^\circ }} p.m.\\\lambda_{e}=\frac{87.7401}{18.935} = 4.63 p.m.](https://tex.z-dn.net/?f=%5Clambda_%7Be%7D%3D%5Cfrac%7B7.33%5Ctimes%2011.97%7D%7B%5Csqrt%7B7.33%5E%7B2%7D%2B11.97%5E%7B2%7D-2%5Ctimes%207.33%5Ctimes%2011.97%5Ctimes%20cos157%5E%5Ccirc%20%7D%7D%20p.m.%5C%5C%5Clambda_%7Be%7D%3D%5Cfrac%7B87.7401%7D%7B18.935%7D%20%3D%204.63%20p.m.)
This is the de Broglie wavelength of the electron after scattering.