Coulomb’s Law - Discovered that magnitude of the electrical force between two charged particle is directly proportional to the product of the magnitudes of the charges and inversely proportional to the square of the distance between them. - Gives the electric force between two point charges. Force of repulsion – both positive; both negative. Force of attraction – negative and positive. - The greater the number of lines of force, the stronger the electric field. Electric Field Due to Point Charge – defined as the force that a test charge will experience when place to a certain point. Electric Field inside a Conductor - Faraday demonstrated that the electric field is zero inside a closed conducting surface and that an excess charge place on a solid conductor resides entirely on its surface. Electric Flux – comes from the Latin word fluxus. Measures the number of field lines passing through a surface. It is the product of the electric field and a vector. The distraction of area vector is the same as that of vector perpendicular to the area. Electric Potential Energy Superstition Principle – states that each will exert a force on another charges if no other charges are present. The total force that a particular charge experiences due to a collection of charges is the vector sum of all individual forces. Electric Field Electric force is a noncontact force. The space surrounding a charged body is called an electric field. An electric field caused any charged particle placed in it to experience an electric force. Michael Faraday – scientist who made important discoveries on electricity and magnetism, introduced the use of electric lines of force to map out an electric field. PROPERTIES OF ELECTRIC LINES OF FORCE - Lines of force start positively charged particles and end on negatively charged particles continue toward infinity. - Lines of force neither intersect nor break as they pass from one charge to another. Gravitational force and electrostatic force are both conservative forces. For conservative force, there is an associated potential energy U. The associated potential energy for gravitational force is the gravitational potential energy. Thus, electric potential energy that is analogous to the gravitational potential energy exists. GPE -> U = mgh Electric Potential energy – similar to gravitational potential energy – both involves field forces. Gravitational potential energy – a result of interaction between masses. It depends on the mass and field strength and the relative position. Electric potential also called electrostatic potential or simply potential at any point in an electric field E is electric potential energy per unit charge at that point. Electric potential is designated as V. - It is a scalar quantity. Its SI unit is volt named after Alessandro Volta. 1V = 1 joule/coulomb Potential difference is the difference in the amount of energy that charge carriers have between two points in a circuit. Equipotential lines - The electric potential can be represented diagrammatically by drawing equipotential lines or in three dimensions, equipotential surfaces. An equipotential surface is one on which all points are at the same potential. Electron Volt, a unit of energy - Electron Volt (eV) is define as the energy acquired by a particle carrying a charge whose magnitude equals that on the electron (q = e) as a result of moving through a potential difference of 1V. - 1eV = 1.6x10 -19 J The Gaussian Surface and Gauss’s Law - Closed surface of various shapes can surround the charge. Only S is spherical. Gauss’s Law - a German scientist, Carl Friedrich Gauss formulated a law, which relates electric field, electric flux, and electric charge. It states that the total electric flux through a surface is the total electric charge inside the surface divided by the constant value of permittivity of free space. Electric Charge - basic property of matter carried by some elementary particles that governs how the particles are affected by an electric or magnetic field. Electric charge, which can be positive or negative, occurs in discrete natural units and is neither created nor destroyed. Dipole – a separation of opposite electrical charges. A dipole is qualified by its dipole moment. A Dipole moment is the distance between charges multiplied by the charge. The unit of the dipole moment is the debye, where 1 debye is 3.34x10^-30C m, The dipole moment is a vector quantity that has both magnitude and direction. Capacitor – important element in an electric circuit. - A device for storing charges. The standard symbol for capacitor. - Parts of the capacitor includes separator, container, cathode foil, anode foil, and terminals. Capacitance – the ability of a capacitor o store charges. It is the ratio of the amount of charge to the potential difference between plates. - CAPACITANCE OF A PARALLEL PLATE CAPACITOR IS AFFECTED BY THE FOLLOWING FACTORS: 1. The bigger the area of the plates, the greater the capacitance. 2. The closer the plates to one another, the greater the capacitance. 3. The higher the permittivity constant, the greater the capacitance. Dielectrics is insulating material or a very poor conductor of electric current. When dielectrics are placed in an electric field, practically no current flows in them because, unlike metals, they have no loosely bond, or free, electrons that may drift through the material. Instead, electric polarization occurs. Dielectric breakdown. There is a limit to the potential difference between the plates of the capacitor. When the maximum potential difference exceeded, the dielectric becomes a conductor, allowing the flow of charges. These moving charges from sparks or discharge. Lightning is an example. Series Circuit. In series circuit, there is only one path for the current to take. Advantage: simple to design and build. Disadvantage: if one light goes out, they all go out; as more lights are added, they become dimmer. - - Dielectric means the material will polarise when in contact with an electric field. The SI unit for capacitance is the farad F named after Michael Faraday which is equal to 1 coulomb per volt. One path for charge transfer through terminals A and B. All the series capacitor acquire the same charge. The charge in each capacitor are equivalent, and all are equal to the total charge in the combination. They have different capacitances, the potential differences between the plates of the capacitor are different. Parallel Circuit. A parallel circuit is one that has two or more paths for the electricity to flow, the loads are parallel to each other. If the loads in this circuit were light bulbs and one blew out, there is still current flowing to the others because they are still in the direct path from the negative to positive terminals of the battery. - - There are several paths for the transfer of charges through the voltage terminals A and B. Since the capacitors are connected to the same terminals A and B, then the potential differences between their plates are equivalent, and are equal to Vtotal. In charging a capacitor, the charges move from one plate directly onto the other plate. Electrodynamics – study of phenomena associated with charged bodies in motion and varying electric and magnetic fields, since a moving charge produces a magnetic field, electrodynamics is concerned with effects such as magnetism, electromagnetic radiation, and electromagnetic induction. Voltage - defined to be the charge rate of doing work. Energy required to move a unit charge through an element. Measured in volts (V). - Voltage may be constant /varying. 1 volt = 1 joule/coulomb = 1 newton meter/coulomb. Current – is the rate at which charge flows through a surface. The word current is often used by itself instead of the longer, more formal “electric current”. Resistance – is a measure of the opposition to current flow in an electrical circuit. Resistance is measured in ohms, symbolized by the Greek letter omega (Ώ) - Ohms are named after Georg Simon Ohm (1784 – 1854), a German physicist who studied the relationship between voltage, current, and resistance. OHM’S LAW – defines the relationship between voltage, current, and resistance. These basic electrical units apply to direct current, or alternating current. - Ohm’s Law is the foundation of electronics and electricity. Voltage measured in volts, symbolized by the letters “E” or “V”. Current measured in amps (ampere), symbolized by the letter “I”. Resistance measured in ohms, symbolized by the letter “R”. Electric Current or current: I = q/t - q is the charge in coulombs t is the time in seconds The unit of currents is coulomb/second or ampere (A) - 1A = 1C/s - Unit ampere is named after the French scientist and mathematician, Andre Marie Ampere. He considered the “Isaac Newton of Electricity”. He was the first to describe current as a continuous flow of electricity along a wire. He founded the science of electrodynamics – the study of charged in motion. Conventional Current - According to Benjamin Franklin, introduce the terms positive and negative charges. The electric current was defined as the flow of positive charges from the positive terminal to the negative terminal of a source of voltage. Electron Current - When electron was discovered, it became clear that the current in a metallic conductor is actually a flow of electron from the negative terminal to the positive terminal. - The electron current is equivalent to the conventional current flowing in the opposite direction. Direct current - The current that travels in one direction (at all times) - It supplies by cell or batteries and is commonly used in flashlight, calculators, automobiles and cellphones. Alternating current – Current that changes direction at a regular interval (normally 60 times in one second). It is produces by AC generators and distributed by electric companies like Manila Electric Company (Meralco) and used in most household appliances. Drift Velocity – The velocity associated with the motion of electrons VD (V sub D) - Proportional to the electric field line E. The constant of proportionality µ is called electron mobility. Current Density. J is the current density of a conductor. - - It is defined as the current per unit area. J = I / A = n q Vd (V sub d). This expression is valid only if the current density is uniform and A is perpendicular to the direction of the current. J has SI units of A/m2 The current density is in the direction of the positive charge carriers. Current Density & Drift Velocity. Thus, we can say that drift velocity of the electrons and its current density is directly proportional to each other. Also, when the electric field intensity increases, the drift velocity increases, and the current flowing through the conductor also increases.
