Home 2nd Year Physics Notes Class 12 Physics Chapter 19 Notes – Dawn of Modern Physics

Class 12 Physics Chapter 19 Notes – Dawn of Modern Physics


In this post, I am sharing the Class 12 Physics Chapter 19 Notes PDF for the students of Intermediate Part 2. This chapter’s name is Dawn of Modern Physics. Students can download the Class 12 Physics Chapter 19 Notes PDF on their laptops or mobile. These Physics Notes are for all the boards working under the Punjab Board like Gujranwala Board, Lahore Board, Faisalabad Board, Multan Board, Rawalpindi Board, Sargodha Board, DG Kahn Board, and Sahiwal Board. Here are the complete FSC 2nd Year Physics Notes PDF chapters.

FSC Part 2 Physics Chapter 19 Notes – Dawn of Modern Physics

Class 12 Physics Notes


In the beginning of 20th century, many experimental and theoretical problems relating to physics could not be solved on the basis of Newtonain classical physics. For example the behaviour of matter on the atomic level. The phenimenon of black body radiation, the photoelectric effect and atomic level. The phenomenon of black body readiation, the photoelectric effect and constancy of speed of light could not be expelained in terms of laws of classical physics. To explain these observations new concepts were needed. The study of these concepts is know as modern physics.

What is relative motion?

The change in position of a body with respect to another body is called relative motion. If a ball is thrown up, the up direction is only for that particular place. It will be down position for a person on opposite of 1st observer. This concept of direction is relative. Similarly, rest or motion of object is not passenger while, they are in motion with the respect to observe are stationary on earth. All motions are relative to a person or instrument observing it.

Special Theory of Relativity

In classical mechanics, the velocities of moving objects are negligible as compared to velocity of light. However, relativities mechanics mechanics deals with velocities of moving objects comparable to speed of light. The part of relativistic mechanics which deals with uniform relativestic velocities is called special therory of relativety. On the other hand, the part of relativistic mechanics which deals with accelerated relativistic velocities is called the general theory of relativety.

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