Unit 7 Physics

How are electric force and distance related? How would the force change if the distance between two charges were tripled?

It is inversely related to the square of the distance between charges. It would be one-ninth as great.

How can objects be charged?

by the transfer of electrons (conduction, induction, friction)

What is Coulomb's Law?

the force between two charged particles varies directly with the product of their charges and inversely with the square of distance between them

Grounding

the process of removing excess charge by touching an object to earth

What is grounding?

the removal of excess charge by touching an object to earth

The conductor to be charged is separated...

trapping opposite charges on the two halves

Conductor

A material through which a charge will move easily, for example copper

Insulator

A material through which a charge will not move easily, for example glass

Charges by contact

- applies to insulators (really hard to do with conductors) Explanation: When there is friction between two unlike materials, the one with greater e affinity will gain e from the other material Example: plastic comb takes electrons from wool

Separation of charge on neutral objects (polarization)

-applies to both conductors Explanation: When a charged object comes close to a neutral object electrons shift position; one becomes negative and the other ends up positive, overall is still neutral Example:

Charging by induction

-applies to conductors explanation: 1. Neutralized object is polarized 2. Neutral object is connected to ground and more electrons move into or out of ground 3. Original charge rod is removed, remaining electrons spread out Ex: Bringing a negative plastic rod near neutral electroscope connected to ground becomes positively charged

Charging by conduction

-applies to conductors -Explanation: When a charged object touches a neutral conductor, electrons move in and out and the conductor becomes positive or negative -Example: touching neutral electroscope with negative plastic rod makes electroscope negative

An electric charge of an object can be...

-positive -negative -neutral it is based on the # protons - # electrons

What is an electrical conductor?

A material that allows charges to move about easily -Example: most metals, plasma (ionized gas-lightning) graphite, ionic solutions

Observations on charges

1. Only two kinds of charges (positive and negative) 2. Like charges repel, opposites attract 3. Charges exert forces on other objects at a distance 4. The force is stronger when the charges are closer together

Give an example of charging by polarization. Diagram what the electrons are doing when an object A is being charged by polarization by object B.

A negatively charged object comes near a neutral object. The electrons in the neutral object move to the opposite side of the item leaving a temporary negative and positive side to the object.

Give an example of charging by induction. Diagram what the electrons are doing when an object A is being charged by induction by object B.

A negatively charged object polarizes a neutral object creating a movement of electrons into a positive and negative side. A grounded object (hand) touches the polarized object allowing electrons to leave the object. Aftere the electrons leave the object it has a positive charge.

The law of conservation of charge states that charge is neither created or destroyed. Which of the following statements is consistent with the law?

All charging methods involve the transfer of electrons between two objects

What is an electric field

An action at a distance force; field force

Why do hair and balloon stick together?

Because opposites attract

Anything that has a charge is influenced by what?

By an electric field

How can an object be charged by conduction?

By touching it with a charged object

What is the SI unit of charge?

Coulomb

How are electric force and charge related? Describe the force when the charges are like charges and the force when the charges are opposite charges.

Electric force is directly related to each charge. Like charges repel, opposite charges attract.

A glass test tube is rubbed with a plastic bag. The glass test tube becomes charged with a positive type of charge. During the rubbing process, ________

Electrons are removed from the glass test tube and transferred to the plastic bag

Explain what happens when a balloon is rubbed on your hair. What are the overall charges?

Electrons are transferred from your hair to the balloons surface -The overall charge on your hair is positive -The charge on the balloon is negative

Which statement describes what happens to an object when it becomes polarized?

Electrons move inside the object so that one side becomes positive and the other becomes negative

A negatively charged balloon is brought near to a metal pop can as shown in the diagram at the right. Which statement describes what happens as the balloon approaches the can?

Electrons within the can move away from the balloons side

Coulomb's Law Equation

F=K qa*qb/r², qa and qb refer to the two charges, r is the distance between them , K is constant (9.0x10 ^9), and F is the magnitude of the force between the two charges

T OR F: A negatively charged object does not possess any electrons.

False

T OR F: A negatively charged object does not possess any protons

False

T OR F: A positively charged object does not possess any electrons

False

T OR F: An object that is electrically neutral does not possess any charges inside of it

False

T OR F:A positively charged object does not possess any protons.

False

What is the difference between conductors and insulators? Give 2 examples of each.

In a conductor, electric current can flow freely, in an insulator it cannot. Metals such as copper typify conductors, while most non-metallic solids are said to be good insulators, having extremely high resistance to the flow of charge through them. "Conductor" implies that the outer electrons of the atoms are loosely bound and free to move through the material. Most atoms hold on to their electrons tightly and are insulators. Simply stated, most metals are good electrical conductors, most nonmetals are not.

Give an example of charging by conduction. Diagram what the electrons are doing when an object A is being charged by conduction by object B.

Metal sphere (A) is negativly charged, it touches object B transferring electrons to it leaving both objects negative.

An neutral, aluminum pie plate is held by insulating handle and touched to a negatively charged sphere. what type of charge does the pie plate have once it is pulled away?

Negative

Is an electric charged created or destroyed?

Neither, it is conserved

Do you need friction to have static electricity?

No

When diagramming an electric field, where do positively charged objects electric field lines point?

Point out and going away from the object

Give an example of charging by friction. Diagram what the electrons are doing when an object A is being charged by friction by object B.

Rubber rod rubbing fur, electrons are pulled off fur and stay on rubber rod leaving the rod negative and the fur positive

When diagramming an electric field, where do negatively charged objects electric field lines point?

The field lines go in and towards the object

Fe=

The force acting on a charge particle in an electric field

Fg=

The force acting on an object w mass in a gravitational field

What does it mean to say that charge is conserved?

The net charge of an isolated system remains constant. The only way to change the net charge of a system is to bring in charge from elsewhere, or remove charge from the system.

Where do charges added to a conductor go?

The quickly spread over the surface of the object

What is charging?

The separation, not creation, of electric charges

When diagramming an electric field, how do we know if the charge is strong?

The stronger the charge, the more lines are drawn and they are closer together

Where do charges added on one part of an insulator go?

They remain on that part (examples of insulators include glass, dry wood, plastics and dry air)

electrical insulator

a material through which charge cannot flow easily -Example: Glass, dry wood, most plastics, cloth, dry air

A negatively charged balloon is held near a neutral aluminum can. The opposite side of the can is touched. When touched, electrons move __________

away from the can to the hand

q=

charge of object in the electric field

A vinyl tube is rubbed with animal fur. The vinyl tube is brought near paper bits and observed to attract them. The vinyl tube has been charged with the method of...

conduction

E=

electric field strength

Which type of particle tends to be transferred between (solid) objects?

electrons

g=

gravitational field strength

A charged object will...

induce a separation of charges within a neutral conductor -This process will result in an attractive force between the charged object and neutral conductor (polarization)

m=

mass of object in the gravitational field

What is the net charge of an area with excess electrons?

net negative charge

What is the net charge of an area with a deceit of electrons?

net positive charge

What is static electricity?

separation NOT CREATION of positive and negative electric charges generated by repeated contact and separation between unlike materials