## F.Sc ICS Notes: Physics XII: Chapter 19 Dawn of Modern Physics Numerical Problems

**Numerical Problem 19.1:****A particle called the pion lives on the average only about 2.6 * 10(-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?**

__What is the mass of a 70kg man in a space rocket traveling at 0.8c from us as measured from Earth?__

**Numerical Problem 19.2:**__Find the energy of photon in__

**Numerical Problem 19.3:**
(a) Radiowave of wavelength 100m

(b) Green light of wavelength 550nm

(c) X-ray with wavelength 0.2nm.

__Yellow light 577nm wavelength is incident on a cesium surface. The stopping voltage is found to be 0.25 V. Find__

**Numerical Problem 19.4:**
(a) the maximum K.E. of the photoelectrons

(b) the work function of cesium.

__X-rays of wavelength 22pm are scattered from a carbon target. The scattered radiation being viewed at 85 degree to the incident beam. What is Compton shift?__

**Numerical Problem 19.5:**__A 90 KeV X-ray photon is fired at a carbon target and Compton scattering occurs. Find the wavelength of the incident photon and the wavelength of the scattered photon for scattering angle of (a) 30 (b) 60.__

**Numerical Problem 19.6:**__What is the maximum wavelength of the two photons produced when a positron annihilates an electron? The rest mass energy of each is 0.51 MeV.__

**Numerical Problem 19.7:**__Calculate the wavelength of__

**Numerical Problem 19.8:**
(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.

__What is the de Broglie wavelength of an electron whose kinetic energy is 120 eV?__

**Numerical Problem 19.9:**__An electron is placed in a box about the size of an atom that is about 1 * 10(-10)m. What is the velocity of the electron?__

**Numerical Problem 19.10:**
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