Past IIT JEE Questions - IIT JEE 2008 P1 Q41-43

21

42)

Only the energy corresponding to transition for n = 4 to n = 3 falls in visible region.

So Î»=hc2.64eV=4.8 *10^-7

Hence option C

21

43)

Hint

KE is directly proportional to Z²

30

41) Excitation energy of H atom = -3.4eV + 13.6eV [n₂ - n₁]

= 9.2eV

Energy of He^* in excited state = -13.6 * z²n²

= -13.6* 4/4 = -13.6eV

Energy of He^* after transfer of excitation energy = -13.6eV + 9.2eV

= -3.4eV

-3.4eV = -13.6 * 4n²

n² = 54.43.4 = 16

n = 4

IIT JEE 2008 P1 Q41-43