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Chapter 1 Electricity (1.2 Charged Can Move From One Place to Another…

- - - - the movement of a static charge out of an object
    - - the energy a charged particle has due to its position in an electric field
    - - stored energy an object may have because of its position
    - - the amount of the electric potential energy per unit charge at a certain position in an electric field
        
        measured in units called volts (voltage = electric potential)
    - - potential of one volt = 1 joule of energy per coulomb of charge
    - - high-energy static discharge, static energy caused by storm clouds
    - - a material that allows an electric charge to pass through it easily
    - - a material that does not easily allow a charge to pass through it, also important in electrical safety, keep charges away from the body
    - - the property of a material that determines how easily a charge can move through it
        
        ohms - electrical resistance is measured in these units (Greek letter symbol: Ω (omega)
    - - material that charge can flow through with little loss of energy
    - - practically no resistance at extremely low temperatures, conduct even better than good conductors like copper
        
        can be used in power lines to increase efficiency and conserve energy, and in high-speed trains to reduce friction
    - - providing a harmless, low-resistance path (a ground) for electricity to follow, in may cases, this path actually leads into the ground (Earth)
        
        used to protect buildings from damage by lightning, provides path for electric current to travel into the ground, can absorb the charge and make it harmless, charge then spreads out
    - - energy of motion,
  - - - When a charge moves, it transfers energy that can be used to do work
      - the force of attraction or repulsion between charged particles causes a charge to move
      - to push a charged particle closer to another particle with the same charge takes a certain amount of energy. To push two particles into the same position near that particle takes twice as much energy, and the 2 particles together have 2x as much electric potential energy as the single particle, although the amount of potential energy is higher, the amount of energy per unit charge at that position stays the same
      - just as water will not flow between two towers of the same height, a charge will not move between two positions with the same electric potential, for a charge to move, there must be a difference in potential between the two positions
      - when a charge moves, some of its electric potential energy is used in moving the charge and some of it can be used to do other work
      - Lightning is a type of discharge. Storm clouds may develop very large charges, each with an electric potential of millions of volts
    - - materials resist the movement of a charge in different amounts
      - most materials have some resistance
        
        good conductors have low resistance
        
        good insulators have high resistance
        
        a wire that is thin has more resistance than a wire that is thick
        
        a wire that is long has more resistance than a wire that is short
      - resistance depends on the amount and shape of the material as well as on the material itself
      - by taking advantage of resistance, we can use electric charge to do work
      - if a charge can pass through two different materials, it will pass through the one with the lower resistance
  - - - ex: suppose an object with a negative charge touches an object with a positive charge. The attraction of the unbalanced electrons in the first object to the unbalanced protons in the second object can cause the electrons to move to the second object
    - - (used to lift the water to the top of the tower is stored as potential energy, if you open the pipe below the water, the water moves downward and its potential energy is converted back into kinetic energy)
    - - water in a tower has gravitational potential energy because it is high above the ground
    - - because like charges repel, for example, it takes energy to push a charged particle closer to another particle with a like charge, the energy is stored as the electric potential energy of the first particle, when the particle is free to move again, it quickly moves away, and its electric potential energy is converted back into kinetic energy
      - moving an electric charge through a material can cause the material to heat up, as in a burner on an electric stove
    - - step 1: Charge Separation collisions between particles in storm clouds separate charges. Negatively charged particles collect at the bottom of a cloud
      - step 2: Charge Buildup the negatively charged bottom part of the cloud induces a positive charge in the surface of the ground
      - step 3: Static Discharge the charge jumps through the air to the ground, energy released by the discharge causes thunder and lightning
    - - metals such as iron, steel, copper, and aluminum are good conductors, most wire used to carry a charge is made of copper, which conducts very well
    - - plastic and rubber are good insulators, many types of electric wire are covered with plastic, which insulates well (allows a charge to be conducted from one end of the wire to the other, but not through the sides of the wire)
    - - most buildings have some type of lightning rod (made from a material that is a good conductor), rod is placed high up, so that it is closer to the lightning charge, rod is connected to conductor cable, cable is attached to a copper pole, which is driven into the ground, because of the rod's low resistance, lightning will strike the rod before it will strike the rood, where it might have caused a fire, lightning hits the rod and passes harmlessly through the cable into the ground
- - - - flow of charge, form of electricity used to supply energy in homes, schools, and other buildings, mainly follows same rules as moving static charges
    - - the amount of charge that flows past a given point per unit of time
    - - a type of device that has been developed for producing current, produces electric current using the chemical or physical properties of different materials
        
        electrochemical cell
        
        an electric cell that produces current by means of chemical reactions, contains 2 strips of different materials, strips are called electrodes, electrodes suspended in a third material called the electrolyte, interacts chemically with the electrodes to separate charges and produce a flow of electrons from the negative terminal to the positive terminal, batteries are usually made using electrochemical cells
    - - produce electric current through chemical reactions that continue until one or more of the chemicals is used up
        
        can be dry cells or wet cells (electrolyte is a liquid)
      - include zinc, manganese dioxide
    - - batteries that produce current through chemical reactions that can be reversed inside the battery, rechargeable-car battery
      - include lead sulfate, lead peroxide, lead, sulfuric acid, water
    - - some materials, such as silicon, can absorb energy from the Sun or other sources of light and then give off electrons, producing electric current. Electric cells made from such materials are called solar cells
        
        used to make streetlights come on automatically at night, any houses and other buildings now get at least some of their energy from solar cells, however, it is not always easy or cheap to use that energy
  - - - one concept that does not apply to a moving static charge applies to a current, charge that flows steadily has a certain rate of flow (this rate can be measured)
      - volts can be measured with voltmeter, ohms can be measured with ohmmeter, amps can be measured with ammeter, these 3 instruments are often combined in a single electrical instrument called a multimeter
  - - - Current = Voltage/Resistance, I = V/R, I = current measured in amps, V = voltage measured in volts, R = resistance measured in ohms
- - - - a property that allows an object to exert an electric force on another object without touching it
    - - the space around a particle through which an electric charge can exert this force
        
        strength of field is greater near the particle and weaker farther away
    - - a buildup of electric charge in an object caused by the presence of may particles with the same charge
    - - the smallest unit of a material that still has the characteristics of that material
    - - the total number of unbalanced positive or negative charges in an object, measured in coulombs
        
        1 C is equivalent to more than 10^19 electrons or protons
    - - the movement of electrons through a material
    - - atoms with either a positive or a negative charge
    - - when two uncharged objects made of certain materials - such as rubber and glass - touch each other, electrons move from one material to the other, when one material's electrons are attracted to another material more than they are attracted to their own
    - - the buildup of a charge without direct contact
        
        charged particles push and pull each other through their electric fields without touching, the pushing and pulling can cause a charge to build up in another material, the first charge is said to induce the second charge
    - - induction can build a charge by changing the position of electrons, even when electrons do not move between atoms
  - - - protons = + charge
      - electrons = -charge
      - particles with like charges repel each other, overall charge on atom is neutral
      - particles with unlike charges attract each other, or pull on eachother
    - - a material develops a static charge - or becomes charged - when it contains more of one type of charged particle than another
        
        if there are more protons than electrons in a material, the material has a positive charge
        
        if there are more electrons than protons in a material, the material has a negative charge
      - the amount of the charge depends on how many more electrons or protons there are (net charge)
      - electrons can move easily from one atom to another, protons can not
        
        charges in materials usually result from the movement of electrons (conduction)
      - if electrons move from one atom to another, the atom they move to develops a positive charge, ions are created
      - a static charge can build up in an uncharged material when it touches or comes near a charged material
      - static charges can build up when some types of uncharged materials come into contact with each other
      - scientists have determined from experience which materials are likely to give up or to accept electrons, (on the left, each material tends to give electrons to anything below it on the list and to accept electrons from anything above it), the farther away two materials are form each other on the list, the stronger the interaction
        
        skin
        
        glass
        
        hair
        
        nylon
        
        wool
        
        fur
        
        silk
        
        paper
        
        rubber
        
        polyester
      - induction can produce a temporary static charge, ex:glass rod with a negative charge is brought near a balloon.
        if the electrons cannot return to their original distribution, however, induction can leave an object with a stable static charge, ex:a negatively charged rod approaches two balloons that are touching each other
    - - static charges can be useful in technology, example: photocopy machine, run on electricity that comes to them through wires from the power plant, static charges play an important role in how they work
  - - - can be demonstrated by a balloon and a glass rod
        
        step 1: at first, a balloon and a glass rod each have balanced neutral charges
        
        step 2: when they touch, electrons move from the rod to the balloon
        
        step 3: afterwards, the balloon has a negative charge, and the rod has a positive charge
    - - can be demonstrated by a negatively charged glass rod and a balloon
        
        step 1: the unbalanced electrons in the rod repel the electrons in the material of the balloon
        
        step 2: many electrons move to the side of the balloon that is farthest away from the rod, the side of the balloon with fewer electrons becomes positively charged
        
        step 3: when the balloon moves away, the electrons spread out evenly once again
    - - charging a balloon by rubbing it on your head and then sticking the balloon to a wall
        
        step 1: when you bring the balloon close to the wall, the balloon's negative charge pushes against the electrons in the wall
        
        step 2: if the electrons cannot easily move away from their atoms, the negative charges within the atoms may shift to the side away from the balloon (atoms are polarized)