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PS100 RS 04 Electromagnetic

# PS100 RS 04 Electromagnetic - Chapter 4 The Electromagnetic...

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Unformatted text preview: Chapter 4 - The Electromagnetic Interaction 1 If a feather and a hammer are dropped at the same time on the Moon (in vacuum), a. b. c. d. The hammer hits the ground first The feather hits the ground first The hammer and feather hit at the same time Neither hit the ground Chapter 4 - The Electromagnetic Interaction 2 The gravitational interaction between you and the Earth is strongest a. b. c. When you are standing at sea level. When you are standing on top of Mt. Timpanogos, ~12,000 ft above sea level. When you are sitting in a space shuttle climbing into orbit at a height of 200,000 ft. Chapter 4 - The Electromagnetic Interaction 3 The Electromagnetic Interaction ► Electrification happens all the time. Chapter 4 - The Electromagnetic Interaction 4 Electricity ► Static or unmoving electricity was stored in “Leyden Jars”. Benjamin Franklin used them to show that static electricity and moving electricity, like lightening, were the same. Chapter 4 - The Electromagnetic Interaction 5 The Electric Force Law ► ► ► Gravity only pulls. And it works on objects with mass. The electromagnetic force both pulls and pushes and it works on objects with charge. But the force law is otherwise the same: F = kQq/d2 Q q Q and q represent charge. d which can be positive or negative. As with gravity (G), k is just a number. Chapter 4 - The Electromagnetic Interaction 6 The Electric Force Law ► Objects of opposite charge attract each other. ► Objects of like charge repel each other. Chapter 4 - The Electromagnetic Interaction 7 The Electrical Model of Matter ► At first electricity was thought to be a fluid, like water. ► Experiments done by J. J. Thompson showed this “fluid” to be a stream of charged particles. He broke atoms into positive and negative parts. Chapter 4 - The Electromagnetic Interaction 8 The Electrical Model of Matter ► ► Positive charged “ions” behave individualistically like atoms. Negative charges are always the same regardless of where they come from. The charge of individual electrons was first measured in the Millikan oil­drop experiment in 1909. Chapter 4 - The Electromagnetic Interaction 1.6 x 10­19 coulombs 9 Chapter 4 - The Electromagnetic Interaction 10 The Electrical Model of Matter ► Later it was found that the positive charge carrier was the proton, found inside all atoms. The negative charge carrying electrons are also found in all atoms. What is moving the most to ground the charge? a) Atoms b) Protons c) Neutrons d) Electrons e) Air Chapter 4 - The Electromagnetic Interaction 11 Insulators and Conductors ► Materials that electricity flows through are called conductors. ► Materials that electricity cannot pass through are insulators. Chapter 4 - The Electromagnetic Interaction 12 Contact Force ► Air friction, sliding friction, cutting, touching, pushing, resting on something, connected by a rope, etc. ► It only exists when things touch. Get Very Close! Chapter 4 - The Electromagnetic Interaction 13 Contact Force ► Electromagnetic repulsion between atoms causes the force of contact and sliding friction between objects. Chapter 4 - The Electromagnetic Interaction 14 Do they ever really touch? Chapter 4 - The Electromagnetic Interaction 15 Magnetism ► It has been known for thousands of years that some metals had the ability to permanently attract other similar metals. ► Such metals are called “magnetic” or “ferromagnetic”. Chapter 4 - The Electromagnetic Interaction 16 Magnetism and Field Lines ► The extent ofmagnetic influence is readily described by “field lines”. Such lines can be traced by iron filings. Chapter 4 - The Electromagnetic Interaction 17 The Electromagnetic Interaction ► Hans Christen Oersted discovered that flowing electricity creates magnetism. Chapter 4 - The Electromagnetic Interaction 18 ► ► ► ► Permanent Magnets The easiest way to create a magnet would be to get a piece of iron or other ferro­magnetic material and expose to a strong magnetic field. The strength of the resulting magnet would be directly proportional to both the strength of the original field and the period of exposure. Note that the newly magnetic metal will get weaker and weaker over time. When metal is heated to temperatures above the Curie temperature the domains go away. Chapter 4 - The Electromagnetic Interaction 19 ...
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