Lecture 3

Question 1

What charge does DNA have

Answer 1

negative

Question 2

Polarization of atoms/molecules:
The wall is an insulator so charges cannot
move freely around, but if a positive charged
balloon is brought near….

Answer 2

it will cause the electrons in atoms/molecules on the surface of the wall to be pulled slightly toward the balloon
-This is called induced polarization (of those atoms/molecules)

Question 3

Coulomb’s law only gives the total forces on objects #1 and #2 if they are the only interacting objects and are in ——–

Answer 3

empty space
-If they are in air or water, the presence of the air or later molecules affects the total electric force on each object because there is induced polarization of the molecules and they interact with the objects
-For air K=1.0006, so this effect is tiny and can be ignored
- But for water K=80.4, so the total force will be reduced a lot!
- Important with biomolecules like DNA, RNA, proteins, etc., since they are usually dissolved in water!