Ch. 16 Static Electricity

Give an example of polarization

small particles that are charged that remain on an item (comb that attaches to paper)

When does static electricity charge

at rest

True or False: like charges repel and opposite charges attract

true

Can electric charge be conserved?

Yes, cannot be created/destroyed

Do charges move after they are placed?

No

• in electrostatic charge, charges do not move once placed

What are ways that charges can be separated?

• objects can be rubbed

• think of tape example

Differentiate insulators and conductors

Insulators

• Charges do NOT move

Conductors

• charges are free to move

What are some methods on how to charge?

• contact charging

• non-contact (induced) charging

  • only in conductors (opp. charges attract)

  • ex: electroscope

What term refers to when something can absorb/release a large # of e- without changing its charge appreciable

• give example!

Ground

• ex: earth

What is Coulomb’s law? Explain what each variable is

• k = constant

• Q1, Q2 = charges

• r = distance between 2 charges

If finding magnitude, ignore the signs of the charges

What law applies to Coulomb’s Law?

Newtons 3rd Law (every rxn, has equal/opposite rxn)

• vector quantities

• signs of charges are imp

• G = constant (replace k)

What do you do if there are more than 2 charges?

find the vector sum of all forces acting on it

What is the electric field?

• extends outward from (inward to) every charge and permeates all space

• electric field’s physical effect exert a force on a charge (q) so force created by charge

In an electric field, which way do positives and negatives direct?

Positives face outward

negatives face inward

What do field lines have to do with charges?

• all charges want to move along them

• # of field lines is proportional to magnitude of charge

What happens when the field lines are closer together?

the electric field is stronger

If there were an electric field inside a conductor, what would the charge be? how about in parallel lines?

E inside conductor = 0

• it is “protected” → (think of a cage man)

• in parallel lines, there would be no E (zero)

At what angle are electric field lines always set in respect to the surface?

at 90 degrees

Explain how electric fields apply in DNA replication

• when there are random collisions inside the cell, A =T attract and G=C attract

  • NO other combos

Explain how electric fields apply in photocopy machine

• drum + charged

• image focused on drum

• black areas stay charged and attract toner particles

• image transfers to paper

• sealed with heat

What is an electric flux?

amount of something coming out of a surface depending on angle/surface area

• like water flow, electric, field

When is flux positive and negative?

Flux = positive (less than 90 deg)

Flux = negative (more than 90 deg)

What does Gauss’s Law state for a closed surface?

• it is the total flux through a closed surface depending on the charge enclosed

How does Gauss’s Law work for a sphere?

• Outside of the sphere (r>r0)

  • use equation to find E

• inside of the sphere (r<r0)

  • E = 0