When an electric charge is supported at rest in a static gravitational field, its electric field is not supported with the charge, and it falls freely in the gravitationa field. Drawing the electric field lines continuously in time, we find that they always emerge from the charge, but the electric field is curved and there is a stress force between the freely falling (curved)field and the static charge. The charge radiates
Theories and Experiments The goal of physics is to develop theories based on experiments A theory is a \guess,\expressed mathematically, about how system works The theory makes predictions about how a system should work Experiments check the theories' predictions Every theory is a work in progress
1993年量子力学考研试题 设n)是粒子数算符N=的本征函数,相应之本征值为 n20),算符a和满足对易关系aa-a=1。证明:an)(其中 n≥1)和an)也是N的本征函数其相应的本征值分别为-)和+) 解:用粒子数算符N作用到an)上,即 Nan=aaan=laa a n-a GN n)-an)=(n-1 an 上式表明an)是N的本征态,相应的本征值为(n-1)
1 Faraday's law of electromagnetic induction 1. Experiments ① A magnet and ② two loops of wire,a loop of wire battery and a switch A current is observed in the loop as long as the magnetic flux through the loop is changing with time
