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STD 11 - 2. structure of atom — NEET STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceNEETSTD 11 - 2. structure of atom4 Marks
MCQ
$A$ metal have work function $4\, eV$ is exposed to photon of $\lambda = 1240\,\mathop A\limits^o $. If $a$ accelerating potential of $7.6\, volt$ is applied, then the electron with maximum kinetic energy will have speed equal to -
  • ✓
    $2.18 × 10^6\, m/s$
  • B
    $3 × 10^8 \,m/s$
  • C
    $9.61 × 10^5\, m/s$
  • D
    $8.72 × 10^6\, m/s$
✓

Answer

Correct option: A.
$2.18 × 10^6\, m/s$
a
$E = \left[ {\frac{{12400}}{{1240}}} \right]\,eV = 10\,eV$

$W = 4\, eV$

$KE_{max} = 6\, eV = KE_{initial}$

On applying accelerating potential of $7.6\,V$

$\Delta KE = charge × potential = 7.6\, eV$

$KE_f -KE_g = 7.6\, eV$

$KE_{final} = 7.6\, eV + 6\, eV = 13.6\, eV$

which is $KE$ of electron in $(n = 1)$ in hydrogen atom

$V = 2.188 \times 10^6\, m/s$

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