In this lesson our instructor talks about electric force and charge. First he talks about charge, model of the atom, conservation of charge, elementary charge, and Coulomb's law. Then he talks about conductors and insulators. He also lectures on conduction and induction. Four complete example problems round up this lesson.
Charge, like mass, is a fundamental characteristic. It is tied to the atomic make-up of an object. The unit for charge is the coulomb (C).
Charge comes in two types: positive and negative.
Like charges repel each other (positive & positive; negative & negative), while opposite charges attract (positive & negative).
Electrons have a negative charge, while protons have a positive charge (neutrons have no charge). The amount of charge is equal for electrons and protons, just differing signs. The amount is the elementary charge
e = 1.602 ·10−19 C.
Normally, objects come with an equal amount of positive and negative charge in them, giving the object a net charge of zero. However, it is possible to disrupt this and move some charge off one object on to another. This will leave us with one positively charged object and one negatively charged object.
While it is possible to displace charge, it is not possible to destroy it. Charge is conserved, even if the two types are separated onto different objects.
The amount of force caused by charge is given by Coulomb's law. This force is called the electrostatic force.
F = k·
q1 and q2 are the charges of the objects.
r is the distance between the objects.
k is the electrostatic constant:
k = 8.99 ·109
If the product is negative, they attract; if positive, they repel.
The direction of the force is a direct line from one object to the other.
A conductor is a material where it is very easy to move charge around the material. An insulator is one where it is very difficult to move charge around.
If we have two conductors, one of them charged, and we touch them together, the charge on the first object will spread out evenly between the two of them. This is called conduction.
If we have a charged object and we bring it near a conductor (without touching), we can induce a charge "imbalance" in the conductor. The opposite charge type will move to get near the charged object, while the same charge type will move to get away from the charged object.
Electric Force & Charge
Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.
This book includes a set of features such as Analyzing-Multiple-Concept Problems, Check Your Understanding, Concepts & Calculations, and Concepts at a Glance. This helps the reader to first identify the physics concepts, then associate the appropriate mathematical equations, and finally to work out an algebraic solution.