Physics 100 Lecture 10. Magnetism February 26, 2018

Transcription

1 1 Physics 100 Lecture 10 Magnetism February 26, 2018

2 2 Homework Hint Ch.10 #14 e power plant W electrical Q H e transmission E W delivered electrical e water heater E Q water delivered Work backward: Find Q water, then E delivered, then W electrical, then Q H For those who love math: Q H Welectrical Edelivered etransmission Qwater ewater heater Qwater epower plant epower plant epower etrans- epower etrans- ewater plant mission plant mission heater

3 3 Class Quiz 10: To get the longest lifetime from two batteries and two bulbs you would connect the batteries in and the bulbs in. A. series... series B. parallel... series C. series... parallel D. parallel... parallel Hint: The lifetime of a battery is inversely proportional to the current drawn from it. lifetime constant I

4 4 Class Quiz 10: To get the longest lifetime from two batteries and two bulbs you would connect the batteries in and the bulbs in. A. series... series B. parallel... series C. series... parallel D. parallel... parallel Hint: The lifetime of a battery is inversely proportional to the current drawn from it. lifetime constant I The current from V the battery is I. R Small I corresponds to small V, so connect the batteries in parallel. Small I also corresponds to large R, so connect the resistors in series.

5 5 Magnetism Magnets two poles, like poles repel Earth is a giant magnet magnets are composed of magnets

6 6 Magnetic Fields The force that a magnet exerts on other magnets is described in terms of a field Fields represent forces Gravitational Electric Magnetic Magnetic fields overhead demo and applet magnetic field video

7 7 Which magnetic pole of the Earth is found in Canada? A. north B. south

8 8 Which magnetic pole of the Earth is found in Canada? A. north B. south

9 9 Electric Current and Magnetic Fields Currents produce magnetic fields demonstrations and applet The Right-Hand Rule electromagnets permanent magnets Earth's magnetic field

10 10 Right Hand Rule The magnetic field surrounding a current-carrying straight wire Point your right thumb in the direction of the current Your fingers curl around the wire in the direction of the magnetic field

11 11 A wire carries current directly northward. In which direction does its magnetic field point directly above the wire? A. north B. south C. east D. west

12 12 A wire carries current directly northward. In which direction does its magnetic field point directly above the wire? A. north B. south C. east D. west

13 13 Magnetic Fields and Electric Current Magnets exert forces on currents jumping wire electron beam aurora Aurora photographed by Markus Varik on February 19, 2018 in Tromsø, Norway. From the spaceweather.com real-time aurora gallery

14 14 More about Aurora (optional) Aurora are formed at the poles of the earth where charged particles from the sun spiral around the magnetic fields of the earth and slam into the atmosphere, ionizing the gas molecules and causing them to emit light. The above photo depicts aurora loops around the southern polar region in the distance as viewed by astronauts onboard the space shuttle.

15 15 More about Aurora (optional) Here is a photograph of the northern lights taken by astronauts onboard the International Space Station. The emissions, extending nearly vertically upward, trace out the Earth's magnetic field lines. The green glow occurs at altitudes near kilometers. The red glow is less energetic and occurs at altitude above 250 kilometers. Both types of light are produced by oxygen atoms in the atmosphere: (See a movie!)

16 16 More about Auroras (optional) Photos provided courtesy of NASA, Astronaut Overmeyer and Dr. Hallinan. The source of this material is Windows to the Universe at the University Corporation for Atmospheric Research (UCAR) , 2000 The Regents of the University of Michigan; University Corporation for Atmospheric Research. All Rights Reserved. Of course, auroras are also visible from earth!