Week 1 Day 2 Electricity and Magnetism Vector Fields Surface Wind Gravitational Vector Field Gravitational Force Gravitational Field 6 Scalar and Vector Fields Gravitational Vector eld Temperature Scalar eld Pressure Scalar eld Electrostatic Vector eld Flow Vector eld Electrical Change Electric Force How Do You Get Charged Vector magnitude direction at very point in space How do we represent a vector eld Direction of eld at any point is tangent to the eld line at that point Magnitude of eld at any point is proportional to number of eld lines per unit perpendicular area at that point Field lines never cross each other A scalar eld has a single number assigned to each point in the eld A vector eld has magnitude and direction assigned to each point in the eld Two types of electric charge positive and negative Units of charge Coulomb C Charge of an electron or proton e 1 602 x 10 C where e is called the elementary charge Charge os conserved it cannot be created or destroyed The electric force between charges q and q is repulsive if the charges have the same signs and attractive is the changes have different signs Friction objects become electrically changed by rubbing through adhesion as changes move from one object to another Transfer touching Induction Coulomb s Law Force on q due to interaction between q and q Group Problem Coulomb s Law Vector Analysis Find a vector expression for the unit vectors in terms of and j r r r The Superposition Principle Coulombs Law Worked Example Start with Then solve for the force In Class Problem Force on a Charged object F F F Electric Field Net force on any change is a vector sum of forces from other individual charges Determine an expression for force F on the object 2 due to the interaction with object 3 Three charged objects are located at the positions shown in the gure Find a vector expression for the force on the negatively charged object at P The electric eld at point P due to a charged object source with charge q is the force action on a test point like charge object with charge q at that point P divided by the charge at q E P Superposition Principle Concept Question 5 Equal Charges The electric eld due to a collection of N point charges is the vector sum of the individual electric elds due to each charge E E E E Correct answer 4 Six equal positive charges q sit at the vertices of a regular hexagon with sides of length R We remove the bottom charge The electric eld at the center of the hexagon is Concept Question Electric Field Correct answer 3 Two charged objects are placed on a line The magnitude of the negative charge on the right is greater than the magnitude of the positive charge on the left Other than at in nity where is the electric eld zero To the left of the positively charged object on the left STOPPED HERE IN CLASS Group Problem Electric Field on Axis Symmetry Consider two point charges of equal magnitude but opposite signs separated by a distance d Point P lies along the perpendicular bisector of the line joining the charges a distance s above that line What is the E eld at P Electric Field Lines Concept Question Field Lines Direction of eld at any point is tangent to eld line at that point Field lines point away from positive charges and terminate on negative charges Field lines never cross each other Correct answer 4 Electric eld lines show Direction in which positive charges on those lines will accelerate and paths that charges will follow Force on a Charge Object in an Electric Field Force on a charged object with charge q at a point P in an electric eld E due to a source is F P qE P
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