PS4-2 (SEP 7) In the late 1800’s it was widely believed that all light behaved like waves. However, scientists observed that exposing a sample of metal to a beam of light could knock electrons off the sample. This observation is explained by what is now known as the photoelectric effect which explains that when packets of light energy called photons collide with atoms in a material, electrons are emitted. Scientists first theorized that electrons were absorbing light energy and jumped out of the material with the same amount of energy they absorbed. To their surprise they found that when they shined a brighter light on the substance, the electrons didn’t leave with any more energy! Instead, all the electrons left with the same amount of energy as before but there were just more electrons emitted. Does the photoelectric effect support the wave model of light or the particle model of light? Defend your answer with information from the text.

Search coils and credit cards. one practical way to measure magnetic field strength uses a small, closely wound coil called a search coil. the coil is initially held with its plane perpendicular to a magnetic field. the coil is then either quickly rotated a quarter-turn about a diameter or quickly pulled out of the field. (a) derive the equation relating the total charge q that flows through a search coil to the magnetic-field magnitude b. the search coil has n turns, each with area a, and the flux through the coil is decreased from its initial maximum value to zero in a time ∆t. the resistance of the coil is r, and the total charge is q = i∆t, where i is the average current induced by the change in flux. (b) in a credit card reader, the magnetic strip on the back of a credit card is rapidly “swiped” past a coil within the reader. explain, using the same ideas that underlie the operation of a search coil, how the reader can decode the information stored in the pattern of magnetization on the strip. (c) is it necessary that the credit card be “swiped” through the reader at exactly the right speed? why or why not?