Suppose one food irradiation plant uses a 137 Cs source while another uses an equal activity of 60 Co . Assuming equal fractions of the rays from the sources are absorbed, why is more time needed to get the same dose using the 137 Cs source?
Chapter 6 Core concept Electric and magnetic fields interact and can produce forces 1. Electric charge (q) unit: coulomb (c)- see slide 2 The kind of charge- positive-proton Negative-electron Unit of charge= coulomb o Equivalent to charge of 6.24x10^18 o Metric unit of charge Electron charge o Fundamental charge o Smallest seen in nature o Quantity of charge and the number of electrons An electron charge can be produced by: friction, contact, induction/polarization Slide 3: Charges in matter Inseparable property of certain particles Electrons: negative electric charge Protons: positive electric charge Charge interaction Electric force “like charges repel; unlike charges attract” Ions: non- zero net charge from loss/gain of electrons Slide 11: Coulumb’s law Relationship giving force between two charges Similar to Newton’s law of gravitation K versus G implies gravity weaker Equation 6.2 Charge interaction: like charges repel, unlike attracts [6.1] Quality of charge= (# of electrons) (electron charge) q=ne e= 1.6x10^-19 C Example: 1c = n(1.6x10^-19 C) 1.6x10^-19c 1.6x10^-19c n= 1 1.6x10^-19 n=6.24x10^18 I-clicker questions 1. In an experiment in the late 1800’s, J.J. Thomson discovered that all matter contained negatively charged particles.