7. Electrostatics Flashcards
Electrical charge (q / Q) is measured in coulombs (C). What is the elementary charge (e)? How are coulombs quantized?
The elementary charge is the magnitude of charge possessed in an electron. It equals 1.6 x 10^-19 C. Coulombs can be positive or negative.
Coulombs are quantized which means that they can only equal multiples of the elementary charge.
How much positive charge is contained in a mole of carbon atoms?
1 mole of carbon atoms = 6.02 x 10^23 atoms.
1 carbon atom = 6 protons
elementary charge = 1.6 x 10^-19 C
(+) Charge in a mole of carbon atoms = (6.02 x 10^23 atoms) x (6 protons) x (1.6 x 10^-19 C)
= 55 x 10^4
= 5.5 x 10^5
What is coulombs law?
Coulombs law explains the electric force felt between two charged particles.
Fc = k(Qq) / r^2
k = coulombs constant = 9 x 10^9
Note this is very similar to the force of gravity,
Fg = G(mM) / r^2. The electric force is much stronger than the gravitational force, but acts over very small distances.
What is the principle of superposition with electric forces?
Coulombs law explains the force that one charge exerts on another. What about when 2+ charges exert a force on another charge (Z)?
The principle of superposition explains that we can evaluate the effect each charge has on Z separately, add then take the vector sum of them.
What is an electric field?
The presence of a charged particle alters the chemical space around it. This alteration is called an electric field. When another charge enters this space, it feels an electrical force (coulombs law) exerted by the electric field.
How are electric field lines drawn? What is the significance of their direction?
Electrical field lines are always drawn from (+) to (-) charge. As such, the lines represent the direction of force a positive test charge would feel in the electric field created by some source charge.
What is the formula for electric field (E)?
E = kQ / r^2
Note: It takes two charges to create an electric force, but one charge to create an electric field. If we remove a test charge near a source charge (Q), we are still left with the above equation.
units = N / C
t or f, an electric field produced from a charge, Q, is the same at every distance, r, away from Q.
false. At every distance, r, away from Q, the magnitude of E is the same. However, electric field is a vector and thus, at each point around the charge, E points in a different direction.
t or f, the denser the field lines, the stronger the electric field.
True
What is the formula for finding the electric force exerted by an electric field?
Recall Fc = k(Qq) / r^2 and E = kQ / r^2. The only difference between these formulas is the presence of a test charge. Thus, the force exerted on some charge, q, by the electric field (E) created by Q is
F = E x q (which is really just coulombs law)
t or f, F = ma still applies to any situation handling force.
True. Thus
Fc = qE = ma
What occurs on the inside of a hollow metal box?
Since electrons repel each other, all electrons move to the surface of the metal box to maximize distance between each other. With no excess charge in the body of the system, you block electric fields. Thus, on the inside, E = 0.
What occurs if you bring a positive charge near a conductor or insulator?
conductor = all free electrons move towards the side near the positive charge.
insulator = all atoms become polarized with a delta negative and delta positive side. This is how dipole-induced dipole forces and London dispersion forces work. The dipole of one charged molecule caused polarization in another which causes transient attractive forces
When an object moves “with nature” then PE?
PE decreases when an object moves with nature. All systems prefer low energy states
t or f, sources charges not only produce a vector field (electric field) but they also produce a scalar field.
True - this is called the electric potential (or just potential)
