Physics 1005 Lecture Summary 4/25

Heat Transfer:

Heat naturally flows from hot to cold objects or regions when they are in thermal contact. For example, heat flows into a cooler house from a warmer outside environment, such as from 90°F outside to an 85°F house. Refrigeration requires energy to force heat to flow from a cold to a hot environment.

Vapor-Compression Refrigeration Cycle:

The Vapor-Compression Refrigeration Cycle includes components like an Evaporator (Evaporator Coil), a Compressor, a Condenser (Condenser Coil), and an Expansion Valve (Metering Device). The process involves the evaporator, where low-pressure cold liquid refrigerant extracts heat from the air, causing the refrigerant to evaporate. Next, the compressor pressurizes the gas, making it hotter than the ambient temperature outside. Finally, the condenser releases heat to the outside as the refrigerant gas condenses back.

Electric Charge:

Electric charge is a fundamental quantity, similar to mass. There are two types of charge: positive and negative. Protons carry a positive charge, while electrons carry a negative charge. Charge is a property that particles may or may not possess, like magnetism. The term "charges" often refers to particles that have charge, such as electrons. The unit of charge is the Coulomb (C). Like charges repel each other, whereas unlike charges attract. Electricity and magnetism are related phenomena. Coulomb's Law states that the force between charged objects is proportional to the magnitude of their charges and inversely proportional to the square of the distance between them, represented as F \propto \frac{\text{(charge on object 1)} \cdot \text{(charge on object 2)}}{\text{(distance between objects)}^2}. More charge results in a stronger force, while a greater distance results in a weaker force.

Electric Potential and Voltage:

Charges move in one direction due to electric potential (voltage), analogous to a ball rolling down a hill due to gravitational potential. Electric potential, measured in volts, is the "electric hill" that causes charges to move. Voltage and electric potential are the same thing; voltage is what drives the movement of charges. Batteries supply the electric potential (voltage) to move charges.

Electric Current:

Electric current is the movement or flow of electric charge per unit time, described by the formula \text{Electric current} = \frac{\text{flow of charge}}{\text{time}} . Similar to a water current in a river, electric current in a wire is the flow of electric charge. Water flow is measured in gallons per minute (Gal/min), while electric current is measured in Coulombs per second (C/s), also known as Ampere (A). 1 \text{ ampere} = \frac{1 \text{ Coulomb}}{\text{second}} . For instance, 10 Coulombs of charge passing a point in a wire every second equals a current of 10 amps. Electric potential (voltage) causes current to flow in a wire, highlighting the important distinction between current and voltage.