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## Chapter 21

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**Chapter 21**Electric Charge and Electric Field**Charging an object**• A glass rod is rubbed with silk • Electrons are transferred from the glass to the silk • Each electron adds a negative charge to the silk • An equal positive charge is left on the rod**Charge**+ − Unit: C, Coulomb**Electric Charge**Electric charge is one of the fundamental attributes of the particles of which matter is made.**Electric Field**Electric dipole: Opposite charges (+−) Like charges (++)**3**4 Magnitude of a vector= Length of the arrow**4**-3 5 Vector Components**Decomposing a vector**Hint: Once you know one side of a right-angle triangle and one other angle, you can find all the lengths using cos, sin or tan.**Angles of a vector**Find the angles the four vectors make with the positive x-axis. y 30° x**Write down the following three vectors in ij notation. Find**the sum of these vectors also. 10o 4.5 5 4 50o 60o**5**3 4 (-1) times a vector?**5**4 3 3 4 5**Adding Vectors Diagrammatically**You are allowed to move an arrow around as long as you do not change its direction and length. Method for adding vectors: Move the arrows until the tail of one arrow is at the tip of the other arrow. Trace out the resultant arrow.**Addition of vectors**You are allowed to move an arrow around as long as you do not change its direction.**Adding vectors 1**Add the three vectors to find the total displacement.**Electric field is a vector**The direction of the electric field is given below:**Vector Notation of E field**Charges produce electric field. The closer you are to the charge, the stronger is the electric field. Unit: V/m = N/C q**Store k in your calculator**Type: “8.99E9” then “STO” then “ALPHA” then “K” then “ENTER” If q=2C, r=1.3m, to find the E field, type: “K*2/1.32”**Electric Field (Magnitude)**The magnitude of the electric field produced by a single point charge q is give by: Don’t forget the absolute value! Magnitude is alwayspositive.**Warnings**Observer + −**Example (Continued)**The electric field vector is given by the red arrow.**Example - Two Charges**See supplementary notes