Electricity and Magnetism 3

# Electricity and Magnetism 3 - Electric field and potential...

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Electric field and potential D has largest (magnitude) slope at D so E has largest magnitude points in direction of decreasing potential (to right) E = Δ V Δ x E = Δ V Δ x

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Clicker question I put a + charge at point P Which direction does it move? A) up B) down C) left D) right E) it doesn’t move
Clicker question I put a + charge at point P Which direction does it move? A) up B) down C) left D) right E) it doesn’t move

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Series electrical circuit Any path electrons can flow along is an electrical circuit For the electrical current of electrons to flow, there must be continuity, i.e. no gaps In a series circuit, the circuit elements (in the case on the right, 3 light bulbs) are connected in series The same current flows through each of the bulbs (and through the battery) the current can’t bunch up anywhere just as the flow of water through a pipe can’t bunch up anywhere
Series electrical circuit The current in the circuit is given by The more light bulbs I add in series, the larger the resistance and thus the smaller the current The voltage drop across each resistor is equal to IR Since P=I 2 R, the light bulbs are less bright than if only 1 bulb were in the circuit If one light bulb fails, the circuit fails and on bulbs light up I = V R eq = V R 1 + R 2 + R 3

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Parallel circuits In a parallel circuit, the 3 resistors (light bulbs) are connected in parallel The current of electrons passing through the battery is split into 3 branches The same voltage (in this case the voltage of the battery) appears across each of the light bulbs And since P=I 2 R=V 2 /R, each of the light bulbs glows with the same brightness as if it were in the circuit by itself The more light bulbs I add in parallel, the smaller is the total resistance I = I 1 + I 2 + I 3 = V R eq 1 R eq = 1 R 1 + 1 R 2 + 1 R 3
Household circuits Are wired in parallel, so that multiple appliances can be used at the same time The more appliances connected, the more current is drawn In order to prevent too much current being drawn, a fuse (circuit breaker) is part of the circuit

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Electrical shock Any current passing through your body depends on the voltage difference applied across your body and the electrical resistance of the body Dry skin has an electrical resistance of 100,000 Ω Skin saturated with saltwater
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## This note was uploaded on 10/17/2011 for the course ECON 101 taught by Professor Thompson during the Spring '11 term at Michigan State University.

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Electricity and Magnetism 3 - Electric field and potential...

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