chapter23bnotes

# chapter23bnotes - Zero Resultant Force, Exercise. Do it at...

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Zero Resultant Force, Exercise. Do it at home! s Where is the resultant force equal to zero? s The magnitudes of the individual forces will be equal s Directions will be opposite s Will result in a quadratic s Choose the root that gives the forces in opposite directions

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Electric Field – Introduction s The electric force is a field force s Field forces can act through space s The effect is produced even with no physical contact between objects s Faraday developed the concept of a field in terms of electric fields
Electric Field – Definition s An electric field is said to exist in the region of space around a charged object s This charged object is the source charge s When another charged object, the test charge , enters this electric field, an electric force acts on it

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Electric Field – Definition, cont s The electric field is defined as the electric force on the test charge per unit charge s The electric field vector, E , at a point in space is defined as the electric force F acting on a positive test charge, q o placed at that point divided by the test charge: E = F e / q o
Electric Field, Notes s E is the field produced by some charge or charge distribution, separate from the test charge s The existence of an electric field is a property of the source charge s The presence of the test charge is not necessary for the field to exist s The test charge serves as a detector of the field

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Relationship Between F and E s F e = q E s This is valid for a point charge only s One of zero size s For larger objects, the field may vary over the size of the object s If q is positive, F and E are in the same direction s If q is negative, F and E are in opposite directions
Electric Field Notes, Final s The direction of E is that of the force on a positive test charge s The SI units of E are N/C s We can also say that an electric field exists at a point if a test charge at that point experiences an electric force

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Electric Field, Vector Form s Remember Coulomb’s law, between the source and test charges, can be expressed as s Then, the electric field will be 2 ˆ o e e qq k r = F r 2 ˆ e e o q k q r = = F E r
More About Electric Field Direction s a) q is positive, F is directed away from q s b) The direction of E is also away from the positive source charge s c) q is negative, F is directed toward q s d) E is also toward the negative source charge

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## This note was uploaded on 11/01/2009 for the course PHY phy2049 taught by Professor Wilfredngwa during the Fall '09 term at University of Central Florida.

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chapter23bnotes - Zero Resultant Force, Exercise. Do it at...

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