Q68.Sodium and copper have work functions 2.3eV and 4.5eV respectively. Then the ratio of the wave lengths is nearest to JEE Main 2002 JEE Main Previous Year Paper (1) 1 : 2 (2) 4 : 1 (3) 2 : 1 (4) 1 : 4

Q69.Formation of covalent bonds in compounds exhibits (1) wave nature of electron (2) particle nature of electron (3) both wave and particle nature of electron (4) none of these

Q80.Uncertainity in position of a minute particle of mass 25 g in space is 10−5 m. What is the uncertainity in its velocity (in ms−1)? ( h = 6.6 × 10−34Js) (1) 2.1 × 10−34 (2) 0.5 × 10−34 (3) 2.1 × 10−28 (4) 0.5 × 10−23 Q81. β - particle is emitted in radioactivity by (1) conversion of proton to neutron (2) from outermost orbit (3) conversion of neutron to proton (4) β-particle is not emitted

Q27.The earth radiates in the infra-red region of the spectrum. The spectrum is correctly given by (1) Rayleigh Jeans law (2) Planck's law of radiation (3) Stefan's law of radiation (4) Wien's law