19.1 A particle called the pion lives on the average only about 2.6 ｘ10⁻⁸ s when at rest in the laboratory. It then changes to another form. How long would such a particle live when shooting through the space at 0.95c?[Ans. 8.3 x 10⁻⁸ s)




19.8 Calculate the wavelength of

(a) a 140 g ball moving at 40 m/s
(b) a proton moving at the same speed
(c) an electron moving at the same speed.

(Answer: (a) 1.18 ï½˜ 10⁻³⁴ m  (b) 9.92 nm (c) 1.82 ｘ 10⁻⁵ m)



19.9 What is the de Broglie wavelength of an electron whose kinetic energy is 120 eV?  (Answer: 1.12 ｘ10⁻¹⁰ m)



19.10 An electron is placed in a box about the size of an atom that is about 1 ｘ 10⁻¹⁰ m. What is the velocity of the electron?  (Answer: 7.29 ｘ 10⁶ m s⁻¹)