1. Annihilation is a process in which two anti-particles comes into contact and

Question

1. Annihilation is a process in which two anti-particles comes into contact and gets converted into two photons. In one such experiment you used an electron and positron, each having 10 MeV energy. After annihilation, they produced a pair of photons. What is the wavelength of each photon?

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2. You want to excite an electron in a hydrogen atom from n = 2 energy level to n = 5 level. What should be the wavelength of light you should be shinning on the atom according to Bohr's theory?

0.124pm 0.118pm 0.248pm 0.062pm

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2. You want to excite an electron in a hydrogen atom from n = 2 energy level to n = 5 level. What should be the wavelength of light you should be shinning on the atom according to Bohr's theory?

652 nm 397 nm 486 nm 404 nm 434 nm

Explanation / Answer

1)

let the wavelength produced is wavelength

energy of each photon = 10 MeV

h * c/wavelength = 10 * 10^6 * e

6.626 *10^-34 * 3 *10^8/wavelength = 10 *10^6 * 1.602 *10^-19

wavelength = 1.241 *10^-13 m

wavelength = 0.124 pm

the wavelength of each photon is a) 0.124 pm

2)

let the wavelength needed is wavelength

energy change = -13.6 *(1/n1^2 - 1/n2^2)

h * c/wavelength = -13.6 * e * (1/n1^2 - 1/n2^2)

6.626 *10^-34 * 3 *10^8/wavelength = 13.6 * 1.602 *10^-19 * (1/2^2 - 1/5^2)

solving

wavelength = 4.345 *10^-7 m

wavelength = 434.5 nm

the wavelength of light to be used is 434 nm

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