Hydrogen atoms in the ground state are excited by monochromatic radiation of photon energy 12.1eV. According to Bohr's theory, the spectral lines emitted by hydrogen will be
A
two
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B
three
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C
four
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D
one
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Solution
The correct option is B three When an electron is excited from an energy level ni to an energy level nf then the energy gap ΔE is given by ΔE=13.6Z2(1n2i−1n2f) Energy provided is 12.1eV and Z=1 for hydrogen. Also ni=1 for ground state electrons. Hence 12.1=13.6(1−1n2f) which gives nf=3 Now no. of emissions lines is given by n(n−1)2 Here n=3. Hence no. of spectral lines emitted = 3×22=3