Unit 5: Electrostatics

State Coulomb's law. Explain what each symbol in it stands for, and use it to find the force bewteen a -.002-C charge and a 0.006-C charge that are 10 meters apart

The force between two charge depends directly on the magnitude of each charge and inversely on the square of the distance between the charges. [eq1] is the proportionality constant, q1 and q2 are the magnitudes of the charges, d is the distance... The force between two charge depends directly on the magnitude of each charge and inversely on the square of the distance between the charges. [eq1] is the proportionality constant, q₁ and q₂ are the magnitudes of the charges, d is the distance between the charges, and F is the force between the charges. [eq2]

Ohm's law

V=IR

ammeter

a device used to measure the current flowing through a circuit, must be in series

voltmeter

a device used to measure the potential difference, must be put in parallel

magnetism

ability of a material to attract iron - all electrons of a particular matter spin in the same direction causing the object to become magnetic (SI UNIT - TESLA)

direct current

allows electrons to flow continuously in ONE DIRECTION

circuit

allows electrons to flow from a generated source thru the various component and back to the source

superconductor

allows electrons to flow without resistance (titanium)

conductor

allows electrons/electricity to flow (metals, gold, copper, silver, water)

alternating current

allows flow of electrons to change directions. current oscillates back and forth

Protons and electrons

attract eachother

contact

body charged by friction touches another object

Electrical polarization occurs when

charge distribution in a neutral molecule separates

Two charged particles held close to each other are released. As the particles move, the velocity of each increases. Therefore, the particles have

charges that cannot be determined

open switch

circuit is switched off

closed switch

circuit is switched on

Electrical forces between charges are strongest when the charges are

close together

Lighting bolts occur between

clouds and the ground clouds (both A & B)

voltage

difference between one end of the conductor to the other end of a conductor

battery

direct current supply of voltage and current, usually made of many cells

Coulomb's law says that the force between any two charges depends

directly on the size of the charges and inversely on the square of the distance between the charges or both A & B

The charge distribution in some molecules is permanently separated into positive and negative regions. Such molecules are called

electric dipoles

The fundamental force underlying all chemical reactions is

electrical

resistor

electrical component used to reduce or resist the flow of electricity

diode

electronic device allows current to flow in one direction only

transformer

element used to change the voltage and current in an electric circuit

A material is a good insulator if outer electrons of atoms in the material are free to roam around

false

An atom that is electrically polarized vibrates in only one direction

false

Coulomb's law says that the are two kinds of charges, positive and negative

false

Electrical forces are strong, but in comparison, gravitational forces are stronger

false

The reason electrons are attracted to protons ins that electrons and protons have the same amount of charge

false

When an object is charged by contact, electrons flow from the ground onto the object, or from the object onto the ground

false

A positive charge and a negative charge held near each other are released. As they move, the force on each particle

increases

The reason a charged balloon will stick to a wall is that

induced opposite charges in the wall are closer than other wall charges

Bring a charged object near a conductor and then momentarily touch the conductor. This demonstrates charge by

induction

When a charged cloud passes overhead, the ground below is charged by

induction

Objects can be charged by

induction, friction, and touching (all of the above)

insulator

inhibit or hinder the flow of electrons (wood, rubber)

The net charge of a nonionized atom

is zero

ferromagnetic

material capable of being magnetized (iron nail)

To charge an object by induction, the process of grounding

may or may not occur

ammeter

measures flow of electrons

A positive ion has

more protons than electrons

An electroscope is charged positively, as shown by foil leaves that stand apart. As a negatively charged rod is brought close to the electroscope, the leaves

move closer together

The charge of an electron is

negative

If you comb your hair and the comb becomes positively charged, your hair becomes

negatively charged

To say that electric charge is conserved means that no case has ever been found where

net charge has been created or destroyed

current (I)

number of electrons flowing in a circuit (measured in amperes - A)

Common hydrogen atom consists of

one proton and one electron

series circuit

only one path for electrons to flow, amperage is constant. once interrupted, current no longer flows

Two charged particles held close to each other are released. As they move, the force on each particle increases. Therefore, the particles have

opposite signs

types of magnets

permanent (natural [iodestone] and manmade), temporary, electromagnetic (wire and iron)

A rubbed balloon will stick to a wooden wall, which demonstrates charge

polarization

A negatively charged rod is brought near a metal can that rests on a wood table. You touch the opposite side of the can momentarily with your finger. The can is then

positively charged

volts (V)

potential differences

Atomic nuclei of almost all elements consist of

protons and neutrons

Two charges are separated by a certain distance. If the magnitude of each charge is doubled, the force on each charge is

quadrupled

When the distance between two charges is halved, the electrical force between the charges

quadruples

induction

rearrangement of electrons on an uncharged object in the presence of a charged object (no physical contact)

Two like charges

repel each other

A difference between electrical and gravitational forces is that electrical forces include

repulsive interactions

friction

rubbing fur against a rod

paramagnetic

slightly magnetic material (copper)

To be safe in the unlikely case of a lightning strike, it is best to be inside a building frame with

steel

electrostatics

study of electric charges in stationary form

electrodynamics

study of electricity in motion (measured in A - amperage)

Particle A has twice as much charge as particle B. Compared to the force on particle A, the force on particle B is

the same

Two charged particles held near each other are released. As they move, the acceleration of each decreases. Therefore, the particles have

the same sign

In a good insulator, electrons are usually

tightly bound in place

electrification

too few or too many electrons

A bolt of lightning is a result of charging by induction

true

A material that is a good insulator of electricity is normally a poor conductor of electricity

true

All electrons are identical; all have exactly the same mass and charge

true

Coulomb's law for electrical charges has the same mathematical form as Newton's law of gravitation

true

Semiconductors can be made to conduct electricity and they can also be made to act like good insulators

true

The study of electricity at rest is electrostatics

true

The total amount of charge in the universe is constant. We have never observed a case of net creation or destruction of charge.

true

When we allow charges to move onto or off a conductor by touching it with something connected to Earth, it is common to say that we are grounding it

true

How many different kinds of force would act on a proton placed in both an electric field and a gravitational field

two

parallel circuit

two or more parts for electrons to flow, voltage is constant. if 1 branch is interrupted, current can still flow

power (P)

work done per unit of time (measured in watt [W]) P=IV

semiconductor

works as a conductor in one condition and as an insulator in another condition (silicon)

A conductor differs from an insulator in that a conductor has

• NOT more protons than electrons • NOT faster-moving molecules • NOT more electrons than protons • NOT more electrons than an insulator (NONE of the above)

Much electronic equipment contains transistors and diodes that are made from semiconductors. Semiconductors

• can be very good insulators • can conduct electricity • contain helpful impurities (all of the above)

Charge carriers in a metal are electrons rather than protons because electrons are

• relatively far from a a nucleus • loosely bound • lighter (all of the above)

4 laws of electrostatics

1. unlike charges attract, like charges repel 2. electrons travel on the outside of a conductor 3. electric charges are concentrated on the sharpest curvature of a conductor 4. electrostatic force is directly proportional to the product of charges and inversely proportional to the square of the distance

The electrostatic force between two charges located 8 meters apart is 0.10 N. What will the force be between these charges when they are located 2 meters apart

1.6 N

Two charges separated a distance of 1.0 meter exert a 2.0-N force on each other. If the charges are pushed to a separation of 1/3 meter, the force on each charge will be

18.0 N

A 2-C charge and a 4-C charge attract each other with 10 N of force. How much will a 2-C charge and a 12-C charge attract each other when placed the same distance apart

30 N

Two charges separated by a distance of 1 meter exert a 20-N force on each other. If the charges are pulled to a 2 meter separation distance, the force on each charge will be

5.0 N

Two charges separated by a distance of 1 meter exert a 2-N force on each other. If the magnitude of each charge is doubled, the force on each charge will be

8.0 N

Calculate the electrical force between two electrons that are located on opposite sides of an ionized hydrogen atom. Use the following values for the distance and charge size. distance = 5.3 x 10⁻¹¹ m electron charge = -1.6 x 10⁻¹⁹ C

= 8.2 x 10⁻⁸ N = 8.2 x 10⁻⁸ N

What is the difference between an insulator and a conductor? which would you guess copper is? Wood? Distilled water?

A good electrical conductor is any material composed of atoms with "loose" outer electrons that are freeto move about in the material, such as copper. A good electrical insulator is a material composed ofatoms that tightly bind electrons. Wood and distilled water are examples of good electrical insulators.

List the similarities and differences between Coulomb's law and Newton's law of gravitation

Both law are inverse- square laws and both are directly dependent on the quantities involved; electric charge for electrical force and mass for gravitational force. The Coulomb force is about 1039 times stronger than the gravitational force. Also, the electrical force may be either attractive or repulsive.

The SI unit of charge is the

Coulomb

What are three ways an object can become charged? How does each work? Give examples

Objects can become charged by friction, contact or induction. In charging by friction, two objects are rubbed together, thereby transferring electrons from one object to the other. In charging by contact charge is also directly transferred from one abject to another object. In charging by induction, one objects momentarily grounded while a charged object is located nearby. Rubbing a rubber rod with cat's fur is an example of charging by friction. Touching the charged rubber rod to an uncharged tin can is an example of charging by contact. Holding a charged rod near a tin can and touching the can with your finger is an example of charging by induction.

Why should you not stand or sit in water when using electrical appliances? Why is it not a good idea to talk to your friend on the phone while sitting in a bath?

Ordinary water is a conductor of current. Therefore, when using a plugged-in electrical device, you shouldnot be standing or sitting in water that is connected to Earth. If a short circuit occurs, you may be part ofthe pathway to the ground. For the same reason it is not a good idea to use the phone while taking a bath(although the voltage and current in a phone are relatively low).

magnetic laws

-every magnet has two poles (bipolar) north and south poles -like poles repel and unlike poles attract -force between poles is directly proportional to the product of the pole strength and inversely square of the distance between them

resistances (R)

-measured in ohms - anything that opposes or hinders the flow of electrons -influenced by length of the wire (higher the length, higher resistance), cross section (greater the diameter - less resistance, smaller diameter - greater resistance), material, temperature (temperature increases - resistance increases)

Conservation of charge means that

-electrons by themselves can be neither created nor destroyed -charge can be neither created nor destroyed -the total amount of charge in the universe is constant -no experimenter has ever seen a single charge destroyed by itself