zhang15-2 - 1/10/2010 The electrical force between charges...

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1/10/2010 1 The electrical force between charges can be better understood by introducing the concept of electrical field Just like masses produce gravitational field, charges produce electric field (vector, denoted as ) around it When another charge q 0 (sometimes referred to as a test charge ) enters this electric field, the field exerts a force on the Therefore, although not visible, the electrical field can be “feel” by charges E q F 0 E (SI units of E: N/C) Positive test charge : the force is along the same direction as the electrical field Negative test charge : force and electrical field are in opposite directions Demo (Ping-pong ball in parallel plates) +q E E q F , -q E E q F
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1/10/2010 2 Magnitude of the electrical field (SI units: N/C): This is consistent with Coulomb’s law: Direction of electric field by a point charge The Superposition Principle can be applied to the electric field if a group of charges is present 2 | | | | r q k E e 2 0 2 0 | || | | | | | r q q k r q k q e e | || | | | 0 E q F 2 2 9 2 /C
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zhang15-2 - 1/10/2010 The electrical force between charges...

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