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Transcript
A. Some positive charges in the sweater will move onto the balloon B. Some negative charges in the sweater will move onto the balloon Negatively charged balloon Neutral wall A. B. C. D. Some positive charges in the wall will move towards the balloon Some negative charges in the wall will move towards the balloon Some positive charges in the wall will go onto the balloon Some negative charges on the balloon will go to the wall Negatively charged balloon Negatively charged balloon A. The balloons will move towards each other B. The balloons will move away from each other C. The balloons will not move. A. Most electrons will go into the knob and down to the earth. B. Some electrons will go from the earth through the knob and into the man. All matter is composed of atoms We call different kinds of atoms elements Elements form compounds Compounds have different properties, including different electrical properties The nucleus of an atom is made of smaller particles, such as: ◦ Positive particles called protons ◦ Neutral particles called neutrons Outside the nucleus are negative particles called electrons The makeup of an element will determine how it is electrically charged (will it gain or lose electrons?) If an atom has the same number of electrons and protons it is considered electrically neutral (balance of charges) An atom with unequal numbers of protons and electrons can be considered “electrified” or electrically charged An ion is an atom or molecule that has unequal numbers of protons and electrons An atom with more electrons than protons is negatively charged An atom with more protons than electrons is positively charged Remember, only electrons can move! Protons are tightly bound within the nucleus Like charges repel Unlike charges attract A neutral object will be attracted to any charged object An electric force is due to electric charges Electric force is a non-contact force . . . Objects can experience the force without coming into contact Non-contact forces are often called “field” forces (like the gravitational force) The electrical force is stronger than the gravitational force. Electrical charges collected on an object can be lost to surroundings Gravitational forces can only be detected when observing large bodies like the Earth or sun The electrical force can be either attractive or repulsive The gravitational force is only attractive The process of separating charges into opposite sides within one object One side of an object is positive and the other side is negative One charged object is required to induce electron movement or electron rearrangement Polarization occurs when the molecules within an object reorient based on a nearby charged object Conductors are materials that allow electrons to flow freely Conductive materials will allow charge to distribute across the entire surface of the material This occurs because of the repulsive nature of electrons Conductors can transfer charge to other objects Examples include metals(electrons can be removed easily), salts, water, humans Insulators are materials in which charge will not move easily The charge does not distribute over the object but rather stays in one location Examples include glass, dry wood, plastics, dry air An electroscope consists of a metal knob connected by a metal stem to two thin lightweight pieces of metal foil, called “leaves.” There are 3 ways we can charge objects: ◦ Friction ◦ Conduction ◦ Induction Friction occurs when two objects are rubbed together Electrons transfer from one object to another Both objects are left with an imbalance of charge, one positive and one is negative A charged object comes in contact with a neutral object Excess electrons transfer to the neutral object If a negatively charged object touches another object, the excess electrons transfer to the neutral object The neutral object becomes charged, and is no longer neutral If a positively charged object touches a neutral object, it takes electrons from the neutral object The positively charged object becomes neutral, and the neutral object becomes positively charged (it has lost electrons) Process of charging an object without touching it (bringing one charged object near an neutral object) Electrons are NOT transferred! A ground is simply an object that serves as a seemingly infinite reservoir of electrons The ground is capable of transferring electrons to or receiving electrons from a charged object in order to neutralize that object. Electric force is a vector quantity The closer two charged objects are to one another the larger the electric force The further away two charged objects are from one another the smaller the electric force Inverse relationship Direction of the Electrical Force: ◦Dependent upon whether the objects are charged with like charges or opposite charges The charge of an atom can be measured This charge is measured in Coulombs (C) Each electron holds a negative charge of -1.6 x 10-19 Coulombs Each proton holds a positive charge of 1.6 x 10-19 C. States that the that the electrical force between two charged objects is directly proportional to the product of the quantity of charge on the objects and inversely proportional to the square of the separation distance between the two objects Assume that any collection of charges is located in the center of an object F = Force k = constant, based on the medium the object is immersed in (air) For air, the value of k = 9.0 x 109 N·m2/C2 Q = charge of each object d = distance separating the objects Johnny’s soccer ball has a positive charge of +6.0 x 10-6 C. Rachel’s soccer bag, with a charge of +3.0 x 10 –6 C, is 3.0 m away. a. Calculate the force on the soccer ball. b. Calculate the force if Rachel’s bag had a negative charge. Q1 = 6.0 x 10-6 C Q2 = +3.0 x 10 –6 C d = 3.0 m k = 9.0 x 109 N·m2/C2 𝐹= F= 𝑘𝑄1 𝑄2 𝑑2 = 9.0 𝑥 109 (6.0 𝑥 10−6 )(3.0 𝑥 10−6 ) 32 We can call the space around a charged object the electric field This space affects other charges as they come near the charged object An object that enters the electric field will experience a force. The size of the force is based on the amount of charge present and the distance between objects The electric field is a vector quantity It has a magnitude and a direction The direction of the field can be measured using a positive test charge (as a standard) http://phet.colorado.edu/sims/charges-and-fields/charges-andfields_en.html To show direction, electric field lines are drawn around the charges within an electric field The electric field is stronger where the field lines are closer together Arrows move away from a positive charge (because a positive charge repels the positive test charge) Arrows point toward a negative charge (because a negative charge attracts the positive test charge) Electric field lines are also called lines of force There is an electric field with a magnitude of 150 N/C. Determine the force on a dust particle having a negative charge of 9.2x10-16 C. You have 7 problems to complete. kQ1Q2 F= 2 d F E= Q Note: If you substitute “F” from the Coulomb’s law equation into the “F” of the electric field equation, you get the following: Review . . . Potential energy is due to an object’s position All energy is measured in joules For an object to gain gravitational potential energy, work must be done on the object Example: a book is lifted into the air and gains gravitational potential energy The energy gained by an electric charge when work is done on the charge is called electric potential energy Work is done on the charge when it is moved against an electric field Example: A negatively charged balloon is pushed toward a Van de Graff generator Once the charge is released, the electric potential energy becomes kinetic energy Electric potential is a comparison of the electric potential energy and the number of charges present A balloon charged by rubbing it on your hair does not have many charges (only about 1 millionth of a Coulomb) Electric potential difference is referred to as voltage (V) A device used to measure electric charge is a voltmeter. v = work E=v Charge d V = electric potential difference (“voltage”) Work = f x d Charge = in coulombs E = electric field D = distance Unit: volt (v) which is equal to j/c A high voltage transmitter Allows us to enjoy television, automobiles, and just about every other electronic device Wireless electrical transmission X-rays, radio, wireless telegraphy all attributed to Nikola Tesla http://www.youtube.com/watch?v=B7yqn89j wZo LIGHTNING http://video.nationalgeographic.com/video/kids/force s-of-nature-kids/lightning-101-kids/ http://www.flickclip.com/flicks/sw eethomealabama2.html Lightning can travel up to 140,000 mph Produce temperatures of 54,000°F Can form fulgurites (sand into glass) Transfers 15 C of electric charge Charges are polarized within a cloud The top of the cloud becomes positively charged The bottom of the cloud becomes negatively charged The electric field induces a movement of electrons from the cloud down toward Earth The electric field causes ionization of the air surrounding the cloud This results in a conductive substance called plasma The lightning bolt begins as a step leader or flow of electrons from the cloud toward the ground A positive streamer rises up from the ground When the step leader and the streamer meet, a conductive pathway allows the excess electrons to move to the earth http://www.teachersdomain.org/asset/phy03 _vid_lightning/ Make a lightning strike http://environment.nationalgeographic.com/ environment/natural-disasters/lightninginteractive/ A lightning rod is a protective measure for tall buildings, farm houses, etc. Used to direct lightning strikes to the ground This allows the excess electrons to flow into the ground and not into the house or building You are safe in a vehicle during a lightning storm. http://www.youtube.com/watch?v=C8xt9AP4 1-A Electrical energy can be stored in a device called a capacitor Capacitors are found in nearly all electronic devices ◦ Televisions, camera flash, computer A capacitor must be charged A capacitor is discharged when a conducting path is provided between the plates A device that stores charge Made of 2 conductors separated by an insulator The charge stored will SHOCK you if you are in the conducting pathway!! Found in many electrical circuitscomputers, televisions, camera flashes