Physics Study Guide 3 Heat o Convert different temperature scales from one to another. Fahrenheit to Celsius: (32°F − 32) × 5/9 = 0°C Example: 56 Fahrenheit to ? C (56°F-32)*5/9 = 13.33C Celsius to Kelvin: 0°C + 273 = 273K Example: 56 Celsius to ? K 56°C + 273 = 329K Entropy - Whenever energy freely transforms from one form to another, the direction of transformation is toward a state of greater disorder and therefore toward one of greater entropy o Describe thermal expansion and how it relates to temperature. Thermal expansion - where an object expands and becomes larger due to a change in its temperature. higher temperature means that the molecules are moving faster on average, causing them to take up more space. thermal energy in a system can move from lower to higher temperatures, when external work is done on the system. o Define the ideal gas law and describe how it relates pressure, volume, and temperature Enthalpy - The change in thermal energy of a system plus the product of its pressure and volume The term ideal gas refers to a hypothetical gas composed of molecules that: do not attract or repel each other, and themselves (the molecules) take up no volume. Ideal Gas Law o Define heat and relate the heat transferred in materials to temperature. Heat - thermal energy that flows from a substance of higher temperature to a substance of lower temperature. Heat =/= thermal energy Heat is energy in transit Energy transfers are from objects at higher temperatures to lower temperatures o Describe and differentiate between methods of heat transfer. Radiation – the transfer of heat by means of electromagnetic waves. To radiate means to send out or spread from a central location. Whether it is light, sound, waves, rays, flower petals, wheel spokes or pain, if something radiates then it protrudes or spreads outward from an origin. Conduction – heat flow involves the transfer of heat from one location to another in the absence of any material flow. There is nothing physical or material moving from the hot water to the cold water. Only energy is transferred from the hot water to the cold water. Heat transferred by convection = bulk motion of fluids. Hot Objects ONLY contain Thermal Energy and not Heat. Convection – is the process of heat transfer from one location to the next by the movement of fluids. The moving fluid carries energy with it. The fluid flows from a high temperature location to a low temperature location. o Describe the first and second law of thermodynamics and how they relate to energy and work. First Law of Thermodynamics – the heat added to a system is equal to the systems gain in thermal energy plus the work that it does on its surrounding. Second law of thermodynamics – Heat never spontaneously flows from cold substance to a hot substance. Also in natural processes, high-quality energy tends to transform into lower-quality energy order tends to disorder. Third law of thermodynamics - No system can reach absolute Zero. o Apply the laws of thermodynamics to physical situations. For the first law, think of the food you eat, the external work you can do is because of the food we take. But the amount of work you do is the energy left after the energy required for the proper working of the internal systems in our body. Also, for second law, think of the heat that we emit throughout a day, it's an example of the Statement about an engine which cannot convert all of the energy that it takes from a source into work. Melting of ice cube: Ice cubes in a drink absorb heat from the drink making the drink cooler. If we forget to drink it, after some time, it again attains room temperature by absorbing the atmospheric heat. All this happens as per the first and second law of thermodynamics. What is the relationship between water's high specific heat capacity and Europe's climate? Thermal energy is carried in the gulf stream from tropical waters to the North Atlantic where it warms the otherwise cold climate. Static and Current Electricity o Effects of electric charge Atom loses electron(s) Positive Ion. Atom gains electron(s) Negative ion. Electric force An unequal amount of electrons and protons is electrically charged. o Conductors and Insulators Electric Conductors Materials that allow easy flow of charged particles. • electrons of atom outermost are attracted loosely and easily dislodged. • innermost electrons strongly attracted to nucleus Electric Insulators Materials having tightly bound electrons. Electric ChargeConservation of Charge - In any charging process, no electrons are created or destroyed. So, electrons are simply transferred from one material to another. o The electrostatic force: Coulomb’s Law Coulombs Law – For a pair of charged objects much smaller than the distance between them, force between the varies directly as the product charges and inversely as the square of the separation distance F= k q1q2d2 Charge Polarization - Charge Polarization Molecules in solids can’t move from their relatively stationary positions, but their “centers of charge” can move. electric polarization - distortion of charge in the atom or molecule (Distortion noted above as an example) o Electric Field Electric Field - the space that surrounds any charged object • is a vector quantity (having magnitude and direction) • magnitude of field at any point is force per unit charge • obeys the inverse-square law for a point source Field Lines - used to visualize electric field • show direction of electric field—away from positive and toward negative • show intensity of electric field: bunched together field is strongest lines farther apart field is weaker o Electric Potential Electric potential energy - Energy possessed by a charged particle due to its location in an electric field. Work is required to push a charged particle against the electric field of a charged body. (a) The spring has more elastic PE when compressed. (b) The small charge similarly has more PE when pushed closer to the charged sphere. In both cases, the increased PE is the result of work input. Electric Potential Energy Released particle accelerates away from the sphere — electric PE changes to KE Electric Potential Energy Batteries and generators pull negative charges away from positive ones, doing work to overcome electrical attraction The amount of work depends on number of charges and separation distance Work done by a battery or generator is then available to a circuit as electrical PE Electric potential: • electric potential energy per charge • energy that a source provides to each unit of charge Electric potential = electric potential energy charge o Ohm’s Law Potential difference exists when ends of electrical conductor are at different electric potentials. Batteries and generators are common voltage sources. Charges in a conductor tend to flow from higher potential to lower potential. The flow of charges persists until both ends reach the same potential. Without potential difference, no flow of charge. Electric potential difference Example: water from a higher reservoir to a lower one—flow continues until no difference • no flow of charge occurs when potential difference is zero Sustained electric current requires suitable voltage source • works by pulling negative charges apart from positive ones (available at the terminals of a battery or generator) • energy per charge at terminals provides the difference in potential (voltage) to provide “electrical pressure” to move electrons through a circuit. Electric current: the flow of electric charge in metal — conduction electrons in fluids — positive and negative ions measured in amperes One ampere is the rate of flow of 1 coulomb of charge per second or 6.25 billion electrons per second. Electric current may be DC — direct current charges flow in one direction or AC — alternating current charges alternate in direction Accomplished in a generator or alternator by periodically switching the sign at the terminals Electrical resistance - how well a circuit component resists the passage of electric current • defined as the ratio of energy-source voltage to the current moving through the energy receiver • measured in ohms Factors affecting electrical resistance: thin wires resist electrical current more than thicker wires, long wires offer more electrical resistance, materials of wire: copper has a low electrical resistance, so it is used to make connecting wires, while rubber has an enormous resistance as an insulator, higher temperature (greater jostling of atoms), greater resistance. Semiconductors materials that are neither good conductors nor good insulators, whose resistance can be varied Superconductors certain metals that acquire infinite conductivity (zero resistance) at temperatures near absolute zero. Ohm’s Law relationship – The between current, voltage, and resistance Current in a circuit varies in direct proportion to the potential difference (voltage) and inversely with the resistance: V=I*R Electric shock • damaging effects of shock result from current passing through the body • electric potential difference between one part of your body and another part depends on body condition and resistance, which can range from 100 ohms to 500,000 ohms o Electric Circuits Electric circuits: any closed path along which electrons can flow for continuous flow — no gaps (such as an open electric switch) Devices connect to a circuit in one of two ways: Series and Parallel Series: • A single-pathway circuit for electron flow • A break anywhere in the path results in an open circuit; electron flow ceases • Total resistance adds, more devices, less current Parallel: • A branched pathway is formed for the flow of electrons • A break in any path doesn’t interrupt flow in other paths • A device in each branch operates independently of the others • Total current in the branches add Parallel circuits and overloading • Homes are wired in parallel. As more and more devices are connected, more current moves through the wires. Each device can carry a certain amount of current before overheating. Excessive current can result in a fire. Sources/Resources used or recommended: https://www.slideserve.com/skates/chapter-8-static-and-current-electricity-powerpoint-pptpresentation https://quizlet.com/161547621/ch-8-static-and-current-electricity-flash-cards/ https://quizlet.com/233185779/chapter-8-static-and-electric-current-flash-cards/ https://quizlet.com/233202852/chapter-7-heat-transfer-and-change-of-phase-flashcards/?funnelUUID=36da4538-b573-49c8-8a8c-3df1e8d372c8 https://quizlet.com/161547621/ch-8-static-and-current-electricity-flash-cards/
