Electricity

For an electric force to exist both ___ and a ____ must be present

electric charge and field

electric field

envisioned as surrounding every arrangement of charges. The field represents what is difference about the nearby space because those charges are there. this concept treats charges as interacting with the electric field created by other charges. THUS CHARGE CONFIGURATIONS CAN CREATE ELECTRIC FIELDS, AND THESE FIELDS IN TURN CAN EXERT ELECTRIC FORCES ON OTHER CHARGES

charging by induction

involves grounding the electroscope--providing a path by which electrons can escape from (bulb) to ground.

uC

microcoulombs (e-6)

mC

milli coulombs (e-3)

nC

nano coulombs (e-9)

A rubber rod is charged negatively by rubbing it with fur. The rod is then brought close to the bulb of an electroscope without touching it. What is the charge on the leaves of the electroscope?

negative

You develop a negative charge by scuffing your rubber shoes on the carpet on a cool, dry day. You then touch your uncharged friend. How is your friend charged after you touch them?

negative

What is the charge on the bottom plane after the refueling?

negativw

Friction

objects become electrically charged by transfer of charge e- jumps from one insulator to another.

Two aluminum aircraft fly underneath a negatively charged thundercloud as the bottom plane refuels from the top plane through a steel reinforced hose. Assuming lightning does not strike during the refueling, what is the charge on the top plane afterward?

positive

Polarization

separation of positive and negative charge within object, not touching. ex. when you rub a balloon on your sweater, it can stick to the wall. the opposite sign charge on the wall's nearest surface creates a net attractive force. -electrons on balloon do not leave the balloon because its material is a poor conductor

at a location in space, the direction of the electric field is the same as the direction of the electric force that would act on a charge of what sign?

the electric field direction at any location is in the direction of the force experienced by a POSITIVE test charge imagined to be placed at that location

the force that keeps the electrons in orbit around the nucleus is

the electrical force

Why is the static electric field inside a conductor always equal to zero? What would happen if there ever were an electric field inside a conductor?

A conductor is a material where charges (almost always electrons) move freely. Whenever there is a field inside a conducting material, it exerts a force on the electrons and moves them to one side of the object - polarizing the object. The separated charges inside the polarized object create their own internal field, which point in the opposite direction to the external field. Electrons will keep moving until their field is strong enough exactly cancels out the external field, leaving a total field of zero inside the object.

Conduction

by contact; e- jumps from one insulator to another (look at electroscope diagram to help)

conservation of charge

can't create or destroy charges (in most cases)

insulators

charges mostly stay put even the loosest bound electrons are too tightly bound to be easily removed

conductors

charges move easily. valence electrons are loosely bound.

Field don't affect fields they affect____

charges. The strength of the field must be related to the force it exerts on the test charge, but independent of the amount of charge on the test charge.

Why can't electric field lines cross?

crossing a spot would mean that there would be two directions for the force on charge places there--which is impossible

When an object becomes positively charged, what happens to its mass? Does it change or remain the same? If it changes, does it increase or decrease?

decrease

electrical charge of electron

-1.602e-19

other info

-dont have to be conductor to have conduction -friction creates pairs, if one becomes negative the other object has to become positive -can't put friction on conductor because electrons can bounce right back onto conductors

Rules for Interpreting Electric Fields

1) the closer the electric field lines, the stronger the field 2)at any point, the direction of the electric field is tangent to the field lines 3) field lines start at positive charges and end at negative charges 4)electric field lines never cross

Conductors and Electric Fields

1) the electric field is zero inside a charged conductor (under static conditions) -in a conductor, electrons are easy to move. Any E-field inside a conductor makes them move to one side. As they move to one side, they create a field that cancels the external field.

electrical charge of proton

1.602e-19

An electron is located a certain distance away from a proton and feels an electric force, F0. How much force will the electron feel if it is moved to a distance twice as far from the proton?

1/4F0

How much force will the electron feel if it is moved to a spot 1/3 as far away from the proton?

9*F0

the electric field E at any location is defined as follows

E= F on q+/ q+ (in N/C)

to determine the magnitude of the electric field due to a point charge at a distance r from that point charge, use...

E= kq/r^2 (MAGNITUDE OF ELECTRIC FIELD DUE TO POINT CHARGE Q)

coulombs law

Fe= Kq1q2/r^2 -use this in order to find the magnitude of the electric force between two point charges

What is special about the electric field between two charged parallel plates?

The electric field between two charged parallel plates is constant - it has the same strength and direction everywhere between the plates (as long as you stay away from the very edges). This is very distinctive from the field around a point charge, which points in different direction on different sides and gets weaker as you get further away.

How does the electric force compare to the gravitational force? How are they alike? How are they different?

The electric force is similar to the gravitational force in in that they both are capable of attracting two object together and they both obey very similar equations. The electric force is different from the gravitational force because it works between charged objects while the gravitational force works between massive objects. This leads to another difference because there are two types of charge and only one type of mass. The two different types of charge can create forces that repel as well as attracting, while gravity can only attract. In addition, the electric force is fundamentally a lot stronger than the gravitational force - you can begin to see why if you notice how much bigger the constant in Coulomb's Law is than the constant in Newton's Law of Universal Gravitation.

What is an electric field? Why was the idea of an electric field created?

The idea of an electric field was created to explain how two charged particles could exert forces on each other without ever touching. The electric field is the way that one charge particle reaches out and affects another charged particle. You can think of it as extending around a charged particle like the tentacles of an octopus extend around it's body, except that there are more than eight tentacles and they reach out to every point in space

How do you pick up a negative charge by scuffing your sneakers on the carpet? What is happening while you drag your feet across the floor?

This is an example of charging by friction. As your shoes rub across the carpet, the rubber pulls electrons off of the carpet material. This means that your shoes and your body end up with extra electrons compared to protons and an overall negative charge. Of course, the carpet ends up with fewer electrons than protons and an overall positive charge.

You pick up a positively charge metal ball that is resting on an insulated surface and get shocked when you touch it. What happens to create the shock? What is different about you after the shock?

This is an example of conduction. The shock happens as electrons jump from your body because of they are more attracted to the positively charged ball. As the electrons leave your body, you end up with fewer electrons than protons, which means that you have an overall positive charge. The ball was positively charged because it had fewer electrons than protons, but as it steals your electrons it ends with less overall charge than it started with.

While you are hiking in the mountains, a thundercloud with extra negative charges on its lower level forms close to you. You feel your arm hairs start to stand up and run for cover. While ducking under a ledge, you grab a metal handrail embedded in the ground. How are you charged after grabbing the rail? Why?

This is an example of induction. Your hair is standing up because you are getting polarized by the negative thundercloud overhead. The electrons in your body move away from the thundercloud, down into your feet, leaving you with fewer electrons than protons - and a positive charge - in the upper part of your body. When you grab the handrail, you ground yourself and allow your electrons to move into the handrail and the earth - getting even further away from the negative cloud. After you let go of the handrail, you can't get your electrons back. You now have fewer electrons than protons in your body, so you have a net positive charge.

If all objects are composed of charged object (electrons and protons), why are we usually not aware of this fact?

We usually do not notice that we are made up of charged objects because there are two types of charge - positive and negative - and most objects in the world are made up of an equal number of positive and negative charges. This means that when the charged particles push and pull on each other, they pull on one type of charge and push equally hard on the other type. The net effect is that the pushes and pulls cancel out, leaving it as if there were no force. Interestingly, most forces between two objects occur because of the charged particles in one body interacting with charged particles in another body. When the objects get very close, the electrons in the outer layers of each object's electrons are the parts that get closest. Since the electric force gets stronger as the charges get closer, then the repulsion between the electrons becomes stronger than the attraction toward protons and the net force is to stop the objects from getting any closer. This is what we call touching.

charge

ability to push/pull on other charges e=-1e p-+1e

How are charged objects fundamentally different from uncharged objects?

uncharged objects is that charged objects are capable of exerting an electric force while uncharged objects are not.

coulomb

unit of electrical CHARGE