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Phys1011: Voltage and Capacitance : i have these labs without any text book or handouts assigned....

Phys1011: Voltage and Capacitance : i have these labs without any text book or handouts assigned. i would love some insight and help so that i can learn the concepts better and prep for tests thru this.

Introduction to Terms Used in Lab

This week’s lab we will become familiar with using a multimeter to measure Electric Potential or Voltage. Please follow all instructions presented carefully, to avoid injury to the equipment.

We will only be using low-voltage devices and building low-voltage circuits. These simple circuits will be representative of the larger circuits that are used in modern technology.

Before we get into formal definitions, we will be looking at some operational definitions for purposes of this lab.

Voltage – One analogy for circuits that I like to use is that of the game of Monopoly. If you haven’t every played Monopoly, don’t worry – the analogy is simple enough to use without specific reference to the game. You can think of voltage like currency (monopoly money). You will start off with a certain amount of voltage at the positive terminal of a battery and the rule is it all has to be used up when you get back to the negative terminal. In Monopoly, this is similar to getting $200 every time you pass ‘Go’, but spending it all by the time you travel around the board and return to ‘Go’ to collect another $200.

AAA, AA, C and D batteries have approximately 1.5 Volts (V) per battery. In series, two AA batteries will yield 3.0 V. In parallel, they would only yield 1.5 V (but could double the available current). Every element you encounter in a closed circuit will result in a voltage drop. For example, a clear-housing red LED will require approximately 1.6 V to light up. If you start with 3.0 V and encounter a red LED, you would still need to add another element (like a resistor) to use up an additional 1.4 V. Another analogy is to think of circuits like water (hydrological) features. Voltage would be comparable to water height or pressure. With this analogy, the water height would be the highest on the positive side (cathode) of the battery, move around the pipes (wires), losing height every time the water would go over a waterfall (resistance, see below), until it reaches the ground level where the height is zero (anode, negative side of battery). The battery would act like a pump, lifting the water back up to its maximum height on the positive side of the battery. (Voltage symbol: V, Units: Volts or V)

                                   

Current - Current is the flow of (positive) charge through a circuit. It is in the opposite direction of the drift velocity (of negative charge, of electrons). If protons were free to flow in a circuit, one released from the positive terminal of the battery would flow through the wire and be attracted to the negative terminal (remember how a charged particle responds to electric fields; now the fields are contained within the wire). The amount of charge flowing per unit time is the current. The units are Amperes (Amps or A). One Amp is equal to one Coulomb per second! One Amp is a large amount of current. In our circuits, we will be dealing with around 5-35 mA within the wires. (Note: your body acts like a large resistor, so this amount would drop by orders of magnitude within your body - you’re safe with equipment provided in the kits, and using the IOLab unit as power source.). Current flows from high voltage to low voltage within a circuit. In reality, it is electrons flowing through the circuit being attracted to the positive terminal of the battery, and current is the opposite direction of the flow of electrons. Unfortunately, we knew relationships about current, voltage, and resistance before we knew the structure of the atom and that the primary charge carriers were electrons!   Using the water analogy, the current is magnitude and direction of flow of water. Using the monopoly analogy, the current is the number of pieces moving around the game board per time.

(Current symbol: I, Units: Amps or A)

Resistance - like the name states, resistance impedes the flow of electrons around the circuit. A resistor is a component that adds resistance to the circuit. There are a few reasons to do this - one is to limit the current in a circuit, another is to reduce the voltage in the circuit or use up remaining voltage. If we were to attach a 9.0V battery to a 1.8V LED without a resistor, we would likely ‘burn out’ the LED. Resistors are passive, meaning they consume voltage (and electric potential energy) but cannot produce any themselves. Resistors can be placed in any orientation (there is no + or - side to resistor, meaning there is no correct end to place first in a circuit. From the water analogy, resistance is like friction in a pipe (to reduce current) or a waterfall (to lower voltage). A monopoly example would be a property with a house or hotel - you lose your monopoly money and are returning to ‘GO’ with nothing.     
(Resistance symbol: R, Units: Ohms or Ω [uppercase Greek Omega])

Additional Materials Needed:

One 1.5 V or similar battery.


Part I - Building a Simple LED circuit and measuring Voltage

Measure voltage of a ‘AA’ or similar battery. Place the negative lead (black wire and probe) on the anode of the battery (the flat part), and the positive lead (red wire and probe) on the cathode (raised part on the battery).

1. What voltage do you measure? Is this more or less than what you would expect?

Following the diagram below and examples of the video, construct a simple circuit to light an LED.

For the resistor, start with one of the small brown resistors in the Resistor Set bag. Ideally, try the resistor that has the color bands of brown, black, black, brown, gold (1 kΩ). Resistors are non-polarized elements, meaning that it doesn’t matter which direction that you put the resistor in the breadboard.

Directions: Connect a jumper wire from one of the 3.3V ports on the IOLab unit to the breadboard. Pick a row that you wish to start with. For a specific example, I will pick position 6 A. In the same row 6, plug the anode (long leg) of the LED into the row, for example 6 D. (It could also be in 6 B, 6 C, or 6 E).

The cathode (short leg) of the LED will be inserted into another row down the breadboard, for example 10 D. Next we want to connect the resistor to the LED. In row 10, place one end of the resistor (doesn’t matter which one) into one of the four other open spots, for example 10 C. We want to connect a wire to the other end of the resistor, to allow charge to flow back to the IOLab unit battery. Place the free end of the resistor into any free row that it can fit in, which hasn’t been used yet by any other component. For example, I placed the second end of the resistor into 16 C. To complete the circuit, take another wire and place it in an open spot in row 16 (16 A, B, D, or E), and place the other end into one of the GND ports on the IOLab Unit. The GND is the anode of the batteries in the IOLab unit, while the 3.3V port is the cathode.

2. Turn on the IOLab power button. Does the LED light up? If not, try stepping through the specific example or watch the videos of the example. If it does – congratulations! You have built your first circuit using IOLab and components.

3. Measure the voltage of the LED, and the voltage of the resistor. What are these values? What do they add up to? Does this make sense from the introduction to this lab?

4. Switch out the resistor with other resistors in the Resistor Set. What happens to the brightness of the LEDs? We will look at the resistance values of these resistors in a future lab. For now, you can either identify the resistors by the colored bands on the resistor, or just label the resistors 1, 2, 3, and 4. Identify which scenario has the brightest LED and which has the dimmest.

Resistor

Behavior of LED (brightness)

Voltage on LED
(Volts)

Voltage on Resistor
(Volts)

Voltage of the LED plus Resistor
(Volts)

5. What is the role of the resistor in this circuit? Why do you think is it needed?

Part II – Capacitors in Series and Parallel

Capacitors can be added in series and parallel. Please see sections 19.4 and 19.5 on the details of capacitors.

Using your knowledge gained from building the simple LED circuit, build a series connection of capacitors. Hint: capacitors are polarized (directional) like an LED. Replace the LED with one capacitor, and the resistor with the other capacitor.

(Left and Center: Examples of series and parallel capacitive circuits. Right: Example of capacitors in series.)

6. Measure the voltage across both capacitors (the red lead on the positive side of the first capacitor and the black lead on the negative side of the second capacitor) What value is this? Does this make sense?

7. Determine the total capacitance for the two capacitors in series. Calculate the charge stored on each capacitor, and the energy stored in each capacitor. You may assume that the voltage on each capacitor have identical values.

8. Setup a parallel capacitor circuit, based on your understanding of the breadboards. Remember, both anodes need to be connected together, and both cathodes need to be connected together. Take a picture of your setup and include in this worksheet.

9. Measure the voltage across each individual capacitor. What are these values? Do these measurements make sense?

10. Determine the total capacitance for the two capacitors i in parallel. Calculate the charge stored on each capacitor, and the energy stored in each capacitor.

Solutions

Expert Solution

The main basic things you need to learn is about how voltage and current works, the meanings of resistance, what happens when resistances are connected in parallel and when in series, capacitance and their additions.

voltage also called electromotive force, is a quantity of potential difference in charge between two points in an electrical field. current is a flow of electric charge.

resistance is a quality to oppose the flow of current.The more the resistance, the less the current flows. so the voltage loss at that resistance will be more.

when number of resistances are connected in series, the voltage drop will be sum of alll the resistances.

In the lab, you are given a LED and we should connect different resistances. so if the resistance is high, the voltage drop also is high, which eventually reduces the glow of the LED.

if the resistance are connected in parallel, then the voltage drop decreases. which means equivalent resistance decreases.

Now coming to capacitance,It is the phenomena of storaging of electric charge, when number of capacitances are connected in series, the effective voltage drop decreases, unlike the resistance, if number of capacitances are connected in parallel the effective capacitance will increase, thus reducing the voltage drop by maximum.

important formulae:

voltage = current*resistance

in series, Req = R1+R2+R3+.....

in parallel, Req^-1 = R1^-1+R2^-1+...

charge = voltage *capacitance

in series,Ceq = C1^-1+C2^-1+C3^-1+....

in parallel, Ceq= C1+C2+C3+...


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