Electric Charge and Electric Field Notes PDF

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Electric Charge and Electric Field Notes...

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Electric Charge and Electric Field: Supplementary Informa!on 1. First we need to review the basic physics concepts of FORCE: Force: an interaction between two objects results in a force acting on each of the two objects. Unit of force: [F] SI = 1 N (Newton) Forces are vectors and, like any other vectors, are represented by arrows. Vectors can be added using the familiar head-to-tail method. In general, all forces can be placed in two categories: Contact Forces – the objects interacting are in physical contact with each other. Examples of contact forces include frictional forces, tensional forces, normal forces, air resistance forces, and applied forces. Action at a Distance forces – these are known as fundamental forces. In this case the interaction occurs through a force field rather than by “physical contact.” There are four conventionally accepted fundamental interactions: 1. gravitational (https://en.wikipedia.org/wiki/Gravity) , 2. electromagnetic (https://en.wikipedia.org/wiki/Electromagnetism) , 3. strong nuclear 4. weak nuclear

(https://en.wikipedia.org/wiki/Strong_interaction) , and (https://en.wikipedia.org/wiki/Weak_interaction) .

The gravitational force was studied in Mechanics, the first part of the College Physics book. In this course we will discuss the electromagnetic force and we will begin by studying the electrostatic force in this module.

2. ELECTRIC CHARGE (Q) is a Fundamental Quantity SI unit: [Q] SI = 1 C (Coulomb) Properties of Electric Charges: Two types of charges exist: they are called positive and negative Like charges repel and unlike charges attract Nature’s basic carrier of positive charge is the proton. Nature’s basic carrier of negative charge is the electron Electric charge is always conserved Charge is not created, only exchanged Objects become charged because negative charge is transferred from one object to another.

3. Coulomb’s Law

The electrostatic force between two point charges: acts along the line connecting the two charged particles is proportional to the product of the magnitudes of the charges, |q1 |and |q2 | is inversely proportional to the square of the distance, r, between them it is attractive if the charges are of opposite signs and repulsive if the charges have the same signs The Superposition Principle The resultant force on any one charge equals the vector sum of the forces exerted by the other individual charges that are present. Example: Three charges, lie along the x axis as shown: q1 = 6 µC, q2 = -2 µC. Determine the magnitude and direction of the net force on q3 = 1.5 µC.

See the solution to this problem in the file: “Electrostatics Example Problems with Solutions” which you can download from CANVAS.

4. The Electric Field An electric field is said to exist in the region of space around a charged object. When another charged object enters this electric field, the field exerts a force on the second charged object.

Direction of Electric Field The electric field is a vector, its direction is given by the direction in which a test charge will move in that field. A test charge q0 is a small positive charge.

Unit of Electric Field: [E]SI = 1 N/C Electric Field Lines To visualize electric fields: field lines which are lines pointing in the direction of the electric field. The Superposition Principle applies to the electric field if a group of charges is present. Electric fields from different sources add as vectors. Example Find the electric field at a point located midway between the charges when both charges are positive as shown.

See the solution to this problem in the file: “Electrostatics Example Problems with Solutions” which you can download from CANVAS. Uniform Electric Field The electric field between two conducting plates charged with equal and opposite charge is uniform: The magnitude and direction of the field are the same at any point. The field lines are parallel and equidistant The field outside the plates is zero...