Electric Force Vectors and the Nature of Electric Charge

Whiteboard Homework Warmup! Calculate the magnitude of F, the electrostatic force on particle 3.

And now, for the question of the day:

Early Theory of Electric Charge Physicists like Benjamin Franklin and Charles Coulomb believed that electric charge was a fluid. They theorized that when two objects are rubbed together, the fluid travels. Their theory also said that objects that have lots of the fluid are positively charged, and objects that have a lack of the fluid are negatively charged. Coulomb trying to capture electric fluid in a jar (unsuccessfully)

What actually is electric charge? Electric charge is a property of subatomic particles (protons and electrons) that cause them to feel a force when other protons or electrons are present. Since all matter is composed of protons, electrons and neutrons, it is possible for any object to become positively or negatively charged! (but very difficult to accomplish for certain materials) If an object is negatively charged, it means that it has excess electrons. If an object is positively charged, it means that it has a lack of electrons. If an object has an equal number of protons as electrons, then it is electrically neutral.

Elementary particles have two key components 1) Mass Mass gives particles two fundamental properties. a)Mass causes particles to resist being accelerated This is called the property of inertia. b) Mass causes particles to attract all other particles that have mass This if the gravitational property of matter. Protons and neutrons have roughly the same mass as one another, and they have about 10,000 times as much mass as electrons.

Elementary particles have two key components 2) Electric Charge Electric charge gives particles one fundamental property. a)Electric charge causes protons and electrons to create an electric field This means that all other charged particles in their vicinity will feel an electric force Protons and electrons exactly opposite charges to one another. (This shows the complete independence of mass and charge) Neutrons have an electric charge of 0.

Protons and electrons are the fundamental building block of all charged objects. q proton = 1.6 x C q electron = -1.6 x C This is called the elementary charge, e (e = 1.6 x C) No object could ever exist in nature that has a charge of 1 x C Why? The most physics-y way of stating this concept is that electric charge is quantized. The most physics-y way of stating this concept is that electric charge is quantized. Electric charge comes in indivisible “packages” of magnitude e. Any charged object in nature must have a charge that is a direct multiple of e.

Beautiful Whiteboard Physics: Calculate the angle of attack! Draw a force diagram for each sphere, and then derive an expression for the tension in each string, in terms of given quantities and fundamental constants.

Final Whiteboard: Double One of Them! Suppose in the scenario with the hanging charged spheres, one of the spheres had a charge +q, and the other had a charge +2q. The spheres have the same mass. Which of the following shows the equilibrium position that will be reached by the spheres? (A)(B)(C) (D) None of the above are correct.

F q on 2q F 2q on q The magnitude of the electric force exerted on each particle is the same. Newton’s 3 rd Law is a beautiful thing!