What is the energy of the electron revolving in third orbit expressed in eV ?

• 1.51 eV

• 3.4 eV

• 4.53 eV

• 4 eV

An α -particle of energy 5 MeV is scattered through 180° by gold nucleus. The distance of closest approach is of the order of

• 10^-14 cm

• 10^-10 cm

• 10^-16 cm

• 10^-12 cm

Find the de-Broglie wavelength of an electron with kinetic energy of 120 eV.

• 112 pm

• 95 pm

• 124 pm

• 102 pm

What is the wavelength of light for the least energetic photon emitted in the Lyman series of the hydrogen spectrum ? (take, hc = 1240 eV nm)

• 122 nm

• 82 nm

• 150 nm

• 102 nm

If an electron in hydrogen atom jumps from an orbit of level n = 3 to an orbit oflevel n =2, the emitted radiation has a frequency (R = Rydberg constant, c = velocity of light)

• $\frac{8\mathrm{Rc}}{9}$

• $\frac{3\mathrm{Rc}}{27}$

• $\frac{5\mathrm{Rc}}{36}$

• $\frac{\mathrm{Rc}}{25}$

The de-Broglie wavelength of an electron accelerated to a potential of 400 V is approximately

• 0.03 nm

• 0.04 nm

• 0.12 nm

• 0.06 nm

Total energy of electron in an excited state of hydrogen atom is − 3.4 eV. The kinetic and potential energy of electron in this state are

• K = − 3.4 eV, U = − 6.8 eV

• K = 3.4 eV, U − 6.8 eV

• K = − 6.8 eV, U = + 3.4 eV

• K = + 10.2 eV, U = − 13.6 eV

When electron jumps from n = 4 level to n = 1 level, the angular momentum of electron changes by

• $\frac{\mathrm{h}}{2\mathrm{\pi }}$

• $\frac{2\mathrm{h}}{2\mathrm{\pi }}$

• $\frac{3\mathrm{h}}{2\mathrm{\pi }}$

• $\frac{4\mathrm{h}}{2\mathrm{\pi }}$

89.

A particle is dropped from a height H. The de-Broglie wavelength of the particle depends on height as

• H^-1/2

• H⁰

• H^1/2

• H

The energy (in eV) required to excite an electron from n = 2 to n = 4 state in hydrogen atom is

• − 0.85 

• + 4.25

• − 3.4

• + 2.55