Page 1 :
yon, (a) speed of the electron in Bohr’s iets, al 2nke? 0 es, Di Tne n, speed of es oa in Bohr's first (n= 1) orbit ig, a = hi, _ 23.14 x9 x10? «(1.6 x 10°92, ie 6.63 x 10>, , = 2,186 x10° ms, , ) Orbital period of electron in Bohr’s first orbit is, 2nh, , q, , _ 2x 3.14 x 0.53 x 10-1?, 2 2.186 x 108, = 152 x101®s, T= "7,, T, = (2)? %1.52x10-", = 12.16 x 107! =1.22 x10" 5, T, = (3)? x1.52x10°%, = 41.04 x107!® = 4.10 x10 5., , 12.8. The radius of the innermost electron orbit of a, hydrogen atom is 5.3 x 10-1! m What are the radii of the n=2, and n = 3 orbits ? [CBSE D 14C], , Ans. Here, 4 = 5.3 x 10°! m, mh, = 2? x5.3x10! = 212 x10 m, r= 3? x 5.3 x10! =4.77x10 m., 12.9. A 12.75 eV electron beam is used to bombard gaseous, , hydrogen at room temperature. What series of wavelengths will, beemitted ?, , Ans. Here AE =12.75eV, Energy of an electron in nth orbit of hydrogen atom is, , s, , As, , As, , In ground state, n = 1, = - 136 J -agieey, 1, , Energy of an electron in the excited state after, 8 a photon of 12.75 eV energy becomes, E, =- 13.6 + 12.75 =- 0.85eV, , a ee, , 12.29, eclts, , ee eo, , 13.6, ~0a5 "18 oF neg, , a., The possible emission lines are shown in Fig. 12.23,, , 3 ~ O85 eV, ~-15leV, , ~34eV, , ae - 13.6eV, , Fig. 12.23, , Emitted wavelength,, he _ 6.6x10™ x3x10° _ 19.8x10%, E-E, E-E,, , h 19.8x 1076, 43 = cin ata make ace an, (- 0.85 + 1.51) x 1.6 x10, , , , , , , , , , , , , , = 28.409 x 10°’ m = 28409 A, , = 19.8 x10°° _ 198x, 42 "(= 0.85 + 3.4) x 1.610", = 4.8529 x 10°’ m = 4852.9 A 4, 19.8x10"° 198x, , >——_——————*, Ma (0.85 + 13.6) x 1.6 x 10”, , = 0.9706 x 1077 m = 970.6 A, 19.8 x10, —= easiest, Aaa = (Cai 3A) x1.6%10", , = 6.5476 x107m, , a 19.8x