Tag Archives: Atomic Structure

Chemistry

When light of wavelength 248 nm falls on a metal ….

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When light of wavelength 248 nm falls on a metal of threshold energy 3.0 eV, the de-Broglie wavelength of emitted electron is _ _ _ _ $A^\circ $. (Round off to the nearest integer)

[Use $\sqrt 3 = 1.73$, $h=6.63 \times 10^{-34} Js$, $m_e = 9.1 \times 10^{-31} Kg $, $c = 3.0 \times 10^8 ms^{-1}$, $1 eV = 1.6 \times 10^{-19} J$] Continue reading When light of wavelength 248 nm falls on a metal …. →

JEE Main, Physics

JEE Main 2018 Lyman Pfund Series Problem

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If the series limit frequency of the Lyman series is \nu_L , then the series limit frequency of the Pfund series is:

(1) 25\nu_L
(2) 16\nu_L
(3) \frac{\nu _L}{16}
(4) \frac{\nu_L}{25}

[Based on JEE Main 2018]

Solutions

(A) Text Format Solution

We have, \frac {1}{\lambda} \propto \frac {1}{n_1 ^2}-\frac {1}{n_2 ^2}

Or \nu \propto \frac {1}{n_1 ^2}-\frac {1}{n_2 ^2}

In case of series limit, n_2 \to \infty and therefore \nu \propto \frac {1}{n_1 ^2}

For Lyman Series, \nu_L \propto \frac {1}{1^2}

For Pfund Series, \nu_P \propto \frac {1}{5^2}

\therefore \nu_P=\frac {\nu_L}{25}

Hence, Option (4).

(B) Image Format Solution

If the series limit frequency of the Lyman series is nu_L, then the series limit frequency of the Pfund series is:

(C) .pdf Format Solution

JEE-Main-2018-Lyman-Pfund-Series-Problem.pdf