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Energy of an electron is given by

$E=-2.178 \times 10^{-18}J \left(\frac{Z^{2}}{n^{2}}\right)$

Wavelength of light requires to excite an electron in an hydrogen atom from level n=1 to n=2 will be (h= 6.62 x 10^-34 J s and c=3.0 x 10⁸ ms^-1)

A) $1.214 \times 10^{-7}m$

B) $2.816 \times 10^{-7}m$

C) $6.500 \times 10^{-7}m$

D) $8.500 \times 10^{-7}m$

Option A

$\triangle E=2.178 \times 10^{-18}\left(\frac{1}{1^{2}}-\frac{1}{2^{2}}\right)=\frac{hc}{\lambda}$

$2.178 \times 10^{-18}\left(\frac{1}{1^{2}}-\frac{1}{2^{2}}\right)$

=$\frac{6.62\times 10^{-34}\times3.0 \times 10^{8}}{\lambda}=1.21 \times 10^{-7}m$

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