Assuming that 10.0% of a 100-W light bulbs energy output is in the visible range (typical for incandescent bulbs) with an average wavelength of 580 nm, and that the photons spread out uniformly and are not absorbed by the atmosphere, how far away would you be if 500 photons per second enter the 3.00-mm diameter pupil of your eye? (This number easily stimulates the retina.)
Lecture 1: There are 4 fundamental forces in Nature: 1. Gravitational 2. Weak 3. Strong 4. Electromagnetic Electromagnetism is the underlying force behind most observable phenomena Electricity (Lightning, electric current) Magnetism ( Electric Motors, MRI) Radiation (X-rays, Light) Chemistry Electric Charge Electric charges create electric fields Electric fields lead to forces on electric charges Moving electric charges called current create magnetic fields There are two types of charges: Positive and Negative Like charges repel and opposite charges attract Charge is conserved (cannot be created or destroyed) Charge is quantized in units of electron charge e= 1.6 x 10^1Coulombs Solids often have nuclei arranged in a fixed, periodic pattern Electrons can be bound or free When bound it is called an insulator (wood, glass, rubber) When free it is called a conductor ( metal) Qnet= (Np-Ne)e Lecture 2: Newton’s Third Law says: F 1 on 2= -F 2 on 1 Coulomb’s Law gives the force between point charges: It lies along the line connecting the charges Proportional to the magnitude of each charge Inversely proportional to the separation squared 2 F 1 on 2= K*[(q1*q2)/r ] Where K is a constant equal to 8.99 x 10 Nm Principle of Superposition You must consider one pair at a time to figure out the force on a point
