Its All About Charge

Honors Physics took a ride through electric fields and electric potential energy today. As I said, the journey through electricity will be a strange one, as we are going to omit a fair amount of material from the unit and may do things out of order. We found ourselves already in Chapter 18 today, after leaping over 90% of the math in and 40% of the information in Chapter 17. In Chapter 18, we are, again, going to leap over most of the math and only concentrate on the topics that will further a general understanding of static charge and electric current. The bulk of our time in this unit will focus on the more practical aspects of electricity and tomorrow’s lab on Ohm’s Law will let you see how the three main players in electric current, voltage, current and resistance, interact in ohmic and non-ohmic materials. This material in the book is farther ahead than we are currently, but our discussion of voltage today and the bit of reading to which I directed you will be sufficient to understand the theory behind your results. We’ll discuss the lab on Friday and continue on talking about batteries and charge motion.

Physical Science B did their own lab with Ohm’s law and saw clearly that certain materials maintain a very constant relationship between voltage and current throughout a wide range of voltages. For some materials, like the light bulb, the relationship is not the same at low voltages as for high voltages. The slopes of your lines for the resistors fell quite close to the stated values on your resistors, definitely within the resistor tolerances. We’ll discuss the lab in more detail tomorrow and the get some practice working on the mathematics of series and parallel circuits.

Physical Science E reviewed Ohm’s Law and series circuits today and then moved to parallel circuits. Parallel circuits provide multiple paths for charge flow and therefore, we would not expect the current to be the same through each path if the values of the resistance on the paths vary. However, we would expect the voltage across the resistors to be the same, and it would be the same as the potential difference of the power source. We took time to practice the math for parallel circuits and we will review this first thing tomorrow. Then, we’ll add in electrical energy, power and safety.

Physics F and G began their discussion of electricity with an overview of charge and the methods of charging materials. We spend a bit discussing static charge and then turn out attention to electric current. Like Honors Physics, we’ll be picking and choosing from the upcoming chapters, so make sure to pay close attention to your notes package – that will guide you as to the material for which you will be responsible on the assessment.

Homework

Honors Physics A: Read lab protocol sheet
Physical Science B: Complete lab write up
Physical Science E: Read 16.3 in your book and complete the 16.3 Section Review and the Practice on p. 551
Physics F and G: None