Chapter+20+-+Parts+3+&+4

flat Chapter 20 - Parts 3 & 4

= Part 3 =

__Ohm's Law Lab__

 * Purpose** - To find the relationship between pressure difference and flow rate. Also, to find the difference between Ohmic and Non-Ohmic materials.


 * Hypothesis** - I believe that there is a direct relationship between voltage of a power source and the current in the circuit. I have personally witnessed that when more voltage is added to a circuit (i.e. more batteries), the bulbs in the circuit become brighter, showing that current also increases. I believe that Ohmic material is something that follows Ohm's law and Non-Ohmic material is something that does not follow Ohm's law.

Materials - variable power supply, batteries/holders, long and round bulbs and socket, assorted resistors, multimeters, lead wires. Set-up - 1. Set-up the circuit shown above. Use a variable power supply which can change voltage easily. 2. In the resistor spot, use a long bulb, then a round bulb, then a standard resistor, and then another standard resistor (with a different resistance). 3. Using the ammeter, measure the current going through each of the four resistors. Vary the power supply and for each resistor, use at least four different voltages. 4. Record the voltage and current for each measurement on excel. Graph voltage versus current for every resistor and find a least squares regression line for each set of points.
 * Procedure**:

Find my data here:
 * Data**



Note: For the resistors, their theoretical resistance is a range. The range for resistor #1 is 4935Ω to 4465Ω. The range for resistor #2 is 950Ω to 1050Ω. In the data table, I use the middle value for each resistor.


 * Sample Calculations**




 * Graphs**

Bulbs

Resistors

I used two graphs to be more pleasing for the human eye.

The resistors proved to be a good linear fit for the data, shown by the strong r squareds. The equations were a simple y=mx. According to Ohm's Law, voltage is equal to current times resistance. The linear fits shows that the resistors follow Ohm's Law and thus, is Ohmic material. Y is the voltage, while x is the current. That leaves slope to be resistance. These values are pretty close to the theoretical resistance.
 * Analysis** -

The bulbs proved to be a good polynomial fit for the data, shown by the strong r squareds. The lines should be linear, following the V=IR equation talked about before, but they do not. This means that they do not follow Ohm's Law and are non-Ohmic material.


 * Discussion Questions**


 * Conclusion**- I can conclude that my hypothesis was correct, there is a direct relationship between voltage and current in a circuit. The equation of the graph was V=IR and it is certain that resistance remains constant. This means that voltage and current have a direct relationship and that when one increases, the other increases and when one decreases, the other decreases. I can also conclude that my hypothesis was correct regarding Ohmic and Non-Ohmic material. The resistors were ohmic material because they followed Ohm's law by obeying the V=IR equation (as seen in their graphs). The bulbs were Non-Ohmic material because they did not follow Ohm's Law; they did not follow the V=IR equation (as seen in their graphs).

My percent error was very small for the resistors. The percent error was large for the bulbs because they were non-ohmic material, so we will only talk about the resistors. For the resistors, there was a plus or minus 5% error for the actual number of ohms, so the small error in our data was noted. Actually, each of our resistance numbers came within the range of numbers indicated by the resistor. We also had a 0% error for one of the points, showing how little error there actually was. However, there was some error and this was probably due to the ammeter. When we plugged the ammeter into the circuit, we got measurements that had a range of numbers. We had to settle for a value that seemed fit and sometimes it was not always the most accurate value. This was probably the biggest source of error. I would use a ammeter that was more accurate than the one we used (or at least gave us just one value) to minimize error. Also, we could probably use more accurate resistors, considering the manufacturer gave us a margin of error of 5%. This is an application of real-life circuits. This knowledge can help us if we want to study electrical engineering. It can also help us with more background knowledge of how circuits in our own homes work and how resistors play a very important role.


 * Purpose** - To find out how currents split in multi-loop circuits.


 * Hypothesis** - I believe that when a wire splits into two, the current will go through both wires because it now has the option to take two paths. However, it will not be evenly. More charge will flow through the wire with less resistance than the other wire because charge flows where there is less resistance.

Set-up: Circuit A Circuit B Circuit C Circuit D Materials - resistors, wire leads, batteries, multimeter, power supplies, wires
 * Procedure:**

1. Set up the four circuits shown above. 2. Draw a schematic diagram for each. 3. Measure current and voltage in all resistors. 4. Calculate current and voltage in all resistors. 5. Calculate the percent error of the experimental values compared to the theoretical values.


 * Data**




 * Calculations**




 * Sample Calculations**



Percent Error is shown in the data table above. My percent error was usually within 3% to 8% which is not terrible, but is not very good as well. Some values are a bit lower than this range and some are a bit higher.
 * Analysis**


 * Discussion Questions**




 * Conclusion**

I can conclude that my hypothesis was correct and that when a wire splits in two, more charge flows through the wire with less resistance. I'll prove my point with an example from the lab. In circuit B, there is a junction. I have it labeled as current 1 splitting into current 2 and current 3. Current 2 has a 750 ohm resistor and current 3 has a 1000 ohm resistor. Proved in both the experimental and theoretical data, there is a higher flow rate through current 2 because there is less resistance (750 ohms compared to 1000 ohms).

There was a good amount of error in this lab and my results were not very precise. There were two main sources of error. The first came from resistance not taken into account. Although small, there is resistance in the wires and ammeter that I did not take into account. This definitely could have changed the numbers a bit. I also did not factor the internal resistance in the power sources, which is an even larger amount than the other two. The other source was the multimeter. When trying to measure voltage or amps, the multimeter is very fickle. It changes numbers rapidly, the range is very large in many cases, and it sometimes never settles on just one number. It is hard choosing one number for your data with this instrument. I would use a multimeter that is more accurate than the one we use (or at least gives us just one value) to minimize error. I would also somehow take into account the resistance that we left out. This lab could once again give us more insight on how the circuits in our homes truly work.

The basic trend on error in the circuits was that the most occurred in the power sources, as seen in all four circuits (especially circuit A). The least error occurred in circuit B where I proved the relationship between currents well (most of the error fell under 1%), while the most error was seen in circuit C where most of the error was around 10%. Circuits A and D had alright evidence due to the fact that most of the error fell around 6%. However, I do not think that error is the most important thing to focus on in this lab. It was more important to focus on the main idea of how currents split when there are more than one option. More charge flows where there is less resistance.

Summary of Lesson 2 (Electric Current) on Electric Circuits - Method 4
What is an electric current? Electric current is a flow of electric charge through a medium. This usually is moving electrons in a conductor. Current is created when charge moves from an area of high potential to low potential.

What are the requirements of a circuit? A circuit must be a closed conducting loop. This means charge must travel in a loop that has no gaps. The loop must extend from the positive terminal of a power source to the negative terminal. The other requirement is that the circuit is entirely made of conducting materials capable of carrying charge.

How do you measure electric current? As a physical quantity, current is the rate at which charge flows past a point on a circuit. Denoted by I, current is equal to the quantity charge that passes through a point per amount of time. Current is measured using amperes. 1 ampere = 1 coulomb / 1 second

What is power (in electrical terms)? Power is the rate at which electrical energy is supplied to a circuit or consumed by a load. The electrical energy talked about above is supplied to the load by an energy source like an electrochemical cell. A cell does work upon a charge to move it from the negative to the positive side of itself. The work done on the charge is equivalent to the electrical potential energy change on the charge. Thus, electrical power is the rate at which work is done. Power is defined as such: Power is measured using watts. 1 watt = 1 joule / 1 second

What is a common misconception regarding electric circuits? Batteries are not rechargeable. They die when they lose a significant potential difference between their two terminals.

Summary of Lesson 3 (Electric Current) on Electric Circuits - Method 4
What is the journey of a typical electron? Electrons carry charge and the difference in potential is what encourages the electrons to travel from areas of high potential to low potential. On the electron's path, it collides with many atoms of the conducting wire, which discourages normal movement. This causes a zigzag path and a loss of energy.

What is resistance? Resistance is the hindrance to the flow of charge. Flow rate is the result of how much resistance is present. Longer the wire, the more resistance and vice versa. Thinner the wire, the more resistance and vice versa. Materials of the conductor affect resistance as well.

What is Ohm's Law? The equation that goes alongside of Ohm's Law is V=IR. This can calculate current, voltage, and resistance of parts of a circuit. There are such things known as Ohmic material which means that it follows this equation. Non-Ohmic material doesn't follow this equation and has a resistance that is constantly changing depending on the situation.

How does Power fit in with Electrical Resistance? Electrical power is the rate at which electrical energy is supplied to a circuit or consumed by a load. The equation for calculating power is P=VI. This equation can be written when it is combined with the Ohm's Law Equation. P=RI^2 and P=V^(2)/R.

Summary of Lesson 4 (Electric Current) on Electric Circuits - Method 4
What are the circuit symbols? Circuit drawings are used to give a quick picture of a circuit for better understanding. The above symbols are used and connected to create circuit drawings, known as schematic diagrams.

What are the two types of circuit connections? Circuits can be connected in series, which means that each individual charge passes through every resistor. When they are connected in parallel, each charge does not have to pass through every resistor, because the resistors are lined up individually in separate branches. In series, when the number of resistors increase, the current decreases and the resistance increases. In parallel, when the number of resistors increase (more branches), the current increases and the resistance decreases.

Elaborate more on the characteristics of series circuits. Current in a series circuit is the same everywhere in the circuit. Since this is true, the current through one resistor is the same as a current going through another resistor, or the battery. The equivalent resistance of a circuit is the amount of resistance that a single resistor would need in order to equal the overall affect of the collection of resistors. When two resistors are in a series circuit, you can find the equivalent resistance of those two resistors by just adding up their resistance. The voltage drop of the battery is equal to the sum of the voltage drops of the resistors in the circuit.

Elaborate more on the characteristics of parallel circuits. In a parallel circuit, charge divides up into separate branches such that there can be more current in one branch than there is in another. The total amount of current in all the branches when added together is the same as the amount of current at locations outside the branches. The current outside the branches is the same as the sum of the current in the individual branches. It is still the same amount of current, only split up into more than one pathway. The equation for finding equivalent resistance is a bit more tricky this time. It is shown here: 1 / Req = 1 / R1 + 1 / R2 + 1 / R3 + ... For parallel circuits, the voltage drop of the battery is equal to to the voltage drops at every resistor. = = = Part 4 =