Electricity and Magnetism Workshop: Introduction Inquiry-based instruction

1. Electricity and Magnetism Workshop: Introduction Inquiry-based instruction My motivations: Faculty in engineering teach a set of facts and teach students to solve certain problems. This is perfect for job placement, but does not prepare students for lifelong learning. Lifelong learning can be driven by necessity, but its more fun when it is based on inquiry. We WANT to learn more. I seek to learn from you through dialog. My method: I will approach early science from a historical context because early scientists ‘inquired.’

2. Electricity and Magnetism Workshop: Introduction What do we know now about E & M? • Are electricity and magnetism invisible? • Unlike most fields of physics that deal with light and matter, we can not see electrical charges themselves. • We cannot tell by observation that high voltage lines are charged. • We cannot tell ahead of time that touching a metal doorknob will shock us. • But the effects of electricity are all around us. We can feel them. • We know now that • Atoms are composed of positively charged nuclei with orbiting electrons. • Electricity and magnetism are related. • Light can be considered both a wave and a particle (the photon). • All energy (including electrical energy) is quantized. It is important to know that current is defined as the flow of positive charges, although it was later found that in metals, it is the negative charges (the electrons) that move. Electrons traveling in circuits always flow from the negative terminal of the power source to the positive terminal. Think about it like this: since electrons have a negative charge they will flow towards a positive charge. Opposites attract.

3. Electricity and Magnetism Workshop: Introduction The electrical construction of the atom What do we know now? - All matter is constructed of electrical charges. - The atom is constructed of negatively charged electrons orbiting a positively charged nucleus. • The idea of the atom was first devised by Democritus in 530 B.C. • In 1808, an English school teacher and scientist named John Dalton proposed the modern atomic theory. Modern atomic theory simply states the following: • Every element is made of atoms • All atoms of any element are the same • Atoms of different elements are different in size and in chemical and physical properties. • Atoms of different elements can combine to form compounds • In chemical reactions, atoms are not made, destroyed, or changed (this was before nuclear power) because there is Conservation of mass.

4. Electricity and Magnetism Workshop: Introduction The electrical construction of the atom In 1898, Joseph John Thomson postulated that the atom was constructed of a positively charged nucleus with electrons around it. In 1910-1911, Rutherford performed his ‘famous’ gold foil experiment. Ernest Rutherford 1871-1937 Apparatus : What are alpha particles? : http://www.chemsoc.org/timeline/pages/1911.html http://www.epa.gov/radiation/understand/alpha.htm

5. Electricity and Magnetism Workshop: IntroductionRutherford’s Experiment Firstly, alpha particles are a type of ionizing radiation ejected by the nuclei of certain unstable atoms. They have two protons and two neutrons giving them a charge of 2+ (identical to the nucleus of the helium atom). It is a relatively heavy, high-energy particle with a velocity in air that is roughly one-twentieth the speed of light. It is virtually impenetrable which makes it ideal for this experiment because we want these particles to be deflected by the components of the atoms making up the gold foil. Rutherford hypothesized that a beam of alpha particles would pass through thin sections of foil mainly undeflected and some would be slightly scattered by electrons. Studying the scattering patterns would tell something about the distribution of electrons in atoms. This was not the case. He observed instead that the majority of the alpha particles passed through the foil undeflected, some were slightly deflected, a few underwent serious deflections, and others bounced back in the direction from which they came. Rutherford explained this saying the atom’s mass was not uniformly distributed as he previously thought and that most of the atom’s mass and all of its positive charge were instead centered in a very small region, the nucleus. The rest of the atom was empty space with units of negative charge outside the nucleus.

6. Electricity and Magnetism Workshop: Introduction The electrical construction of the atom Rutherford found that the effective radius of the gold nucleus is Rn = 1.5 × 10-14 m While the radius of the gold atom is Ra = 1.5 × 10-10 m Thus, the mass of the nucleus occupies 1 part in 1012 by volume! Do you suppose this is where the expression “I can see right through you!” comes from? http://micro.magnet.fsu.edu/electromag/java/rutherford/index.html