PT UNIT 1 Subunit 3

• Newton’s Universal Law of Gravitation

• Every Object in the universe attracts every other object with a force that (for two bodies) is directly proportional to the mass of each body and that is inversely proportional to the square of the distance between them.

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• Two kinds of charges

• Positive and Negative

• Charges cause electrical force

• Law of Charges: Like charges repel and unlike charges attract.

• the origin of electrical charge is the atom. All matter is made of atoms.

• In the center of the atom is a nucleus that contains positive charged protons.

• The charge of a normal atom is zero.

• Charges can be transferred from one object to another by adding electrons.

• A neutral atom has a zero charge. Adding electrons to a neutral object makes a negative charge object. Taking away electrons from a neutral object makes a positive charged object.

• Principle of conservation of charge: The net charge in an isolated system never changes.

• Coulomb’s Law

• Elementary Charge is the charge of one electron or one proton.

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• A mass as potential if it is moved through a gravitational field.

• A charge has potential if it is moved through an electric field. The field creates an electrical potential between A and B.

• Electrical forces create a voltage difference whenever the positive and negative charge are separated.

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• Voltage act like a force in an electrical system. It causes electrons to move.

• Electrons are negative charged particles found in the outer part of the atom.

• Voltage is the forcelike quantity in electrical systems.

• Voltage is measured in volts.

• A flow of charge is called a current.

• Electric systems are made of (1)Voltage source) (2) conductors (3) Control elements (4) load

• Voltages source-Battery, electrical plug in, generator

• Conductors-wires

• Control element- switch

• Load-appliances, lights, etc

• Electrical circuit is a closed path made by connecting voltage sources, control elements and loads.

• Two types of electricity.

• Direct current (DC) is current that moves in one direction only.

• Alternating current (AC) is current that moves back and forth in the wire.

• Current is movement of electrons.

• Dry cell batteries uses a paste material that contains the chemical that produces the voltage.

• Wet cell batteries use a liquid material that contains the chemical to produce the voltage.

• Primary cells are those cells that cannot be recharged.

• Secondary cells are those cells that can be recharged.

• The terminals of a battery are called electrodes.

• The positive electrode is called the Anode.

• The negative electrode is called the cathode.

• Connecting voltage sources in series so they add together requires that the positive electrode from one source is connected to the negative electrode of the other source.

• Main sources of AC are generators and electrical outlets.

• The rate at which the current is changing back and forth is its frequency (f)

• Units are cycles/sec = hertz

• Voltage difference can be created by• (1) Chemical means –Chemical energy in dry or

wet cells separates the charges to form a positive pole and a negative pole.

• (2) Magnetic/Mechanical– A coil of wire moving in a magnetic field produces a force on electrical charges that separates the positive and negative charges.

• (3) Light- light energy that falls on certain materials causes the separation of electrons from their atoms.

• Voltage is measured by using a volt meter, panel meter and a oscilloscope and a multimeter.