The home experimentation kits that we will send you will allow you to do simple experiments at home in support of your online lab. Doing these simple experiments at home will give you a better understanding of the concepts. The kits are provided free of charge and will be used in support of all 6 experiments.
Experimentation Kit includes:
- Breadboard
- Multimeter
- Power unit
- Jumper wires
- Electrolytic and ceramic capacitors
- Resistors
- Diodes
- Transistors
- Carbon paper
- Pencils
- Batteries
Instructions:
The instructions for the home experiments that you will perform using your kits are provided below. For each experiment, please include your results and pictures in a Word file and submit it to the corresponding assignment on Canvas. You will receive 5 bonus points for each experiment.
Experiment 1: Tracing Equipotential Lines
In this experiment, you will trace equipotential lines on the small carbon paper that was included in your kit.
First, examine the breadboard provided in your kit. Breadboards are commonly used in electronics to prototype circuits without needing to solder parts together on a printed circuit board. You can insert electronics parts such as wires, resistors and capacitors, and connect them together without any other equipment. In the middle section of your breadboard, the pins labeled a through e are all connected together within the same row. Similarly the pins labeled f through j are connected together within the same row. There are also power rails on both the left and right side of the breadboard. These pins are connected together in the vertical direction.
Now, attach the power unit on your breadboard as shown in the picture. Connect the 9V battery with its connector to the power unit and turn it on by pressing the button on it. You should see the led on the power unit turn on. This power unit will provide 5V to the left power rail and 3.3V to the right power rail. We will use the 3.3V output. Turn on your multimeter, and switch it to the DC voltage mode, and measure the voltage you get from the power unit. Take a picture and include this in your report.
Now place the carbon paper on the breadboard, and connect the electrodes drawn on the carbon paper to the power rail as shown (- on the upper electrode, and + on the lower electrode) by pushing the jumper wires into the pins of the breadboard through the carbon paper. The connection between the jumper wire and the carbon paper won’t be perfect this way, so try to use at least two wires for each electrode as shown. Take a picture and include it in your report.
In the final step, start by measuring the voltage difference between the electrodes. You should get a voltage near 3.3V. Keep the black probe on the electrode, move the red probe on the carbon paper, and trace the 3V equipotential line in between the electrodes and in the fringe region below the positive electrode. As you find a point, mark it with your pencil. After you marked all the points, trace them with a curve, take a picture and include it with your report.
Experiment 2: Thickness of the graphite layer
In this experiment, you will determine the thickness of the graphite layer deposited by your pencil when you write or draw something on a piece of paper.
First start by drawing a rectangle as shown in the picture by using the short pencil that was included in your kit. The exact dimensions are not important, but its width (let’s call this W) needs to be small compared to its length and you will need to measure the width. Make sure to place the white paper directly on a hard surface such as your desk, apply good pressure and color the rectangle thoroughly.
Now, switch your multimeter to ohmmeter mode, and try to measure the resistance of this black portion of the paper. The contact between the tip of the probes and the paper won’t be good. So, place the probes tilted on the paper, and make the contact by using the larger area that looks like a cone right at the tip of the probes instead of the tip itself. The connection between the probes and the paper would still add extra resistance, so instead of a single measurement, determine how much the resistance changes if you move one probe by L = 1 or 2 cm.
The resistance of a material is given by R = ρ * L / A, where ρ is the resistivity of the material, L is the length of the strip (how much you moved your probe in the previous step) and A is the cross sectional area. For the strip, the cross section is a rectangle so A = W * t, where t is the thickness of the graphite layer deposited on the paper. In order to determine the thickness, we also need to know the resistivity of graphite.
So, the next step is to determine the resistivity (ρ) of graphite in the pencil by measuring its resistance. To do this, we’ll use the resistance formula again, but this time the cross sectional area can be determined from the diameter of the graphite core. Cut the back of the pencil with scissors or a knife to expose the graphite tip. Use your ohmmeter to measure its resistance, then determine the resistivity of graphite. Next, go back to your previous result and determine the thickness of the graphite layer on the paper.
You can probably expect that this thickness will be quite small. The diameter of a carbon atom is about 140 pm (picometer = 10^-12 m). Determine how many layers of carbon atoms this thickness corresponds to. Include all of your calculations in your report.
Experiment 3: Resistors in series and in parallel
In this experiment, you will build a simple circuit out of resistors, calculate the voltage drop across them and compare your results with the measured values.
In your kit you should have two of 1 kΩ, 10 kΩ and 100 kΩ Ohm resistors. Identify them by using their color codes and include a picture of all of them in your report. You can use the webpage linked below. Note that the resistors included in your kit have a 5 band designation. You can also use your multimeter and directly measure their resistances.
Build the circuit shown on the diagram below on your breadboard, with two 1 kΩ resistors connected in series with two 10 kΩ resistors connected in parallel attached to the 5 V power supply.
By using Kirchhoff’s rules, calculate the voltage drop across each resistor in this circuit, and then by using your voltmeter measure those voltages and see if they agree with your theoretical predictions. What would happen if you replace R1 and R2 with 10 kΩ resistors and R3 and R4 with 100 kΩ resistors?
Make sure to show all your work and include your pictures in your report.
Notes on building a circuit on a breadboard: There are many different ways to build the same circuit on a breadboard. Sometimes you can connect the circuit components together without using any wires and sometimes you must also use jumper wires to set up your circuit. Sometimes, it might be beneficial to use wires, even though they are not needed, to organize your components on your breadboard. Here are two examples for a circuit with only two resistors in series. For the circuit you will build, feel free to use whatever method you prefer.
Experiment 4: Capacitors in series and in parallel
In this experiment, you will build a simple circuit out of capacitors, calculate the voltages across them and compare your results with the measured values.
In your kit, you should have two electrolytic capacitors with nominal capacitances of 2200 μF and 1000 μF. Identify them, measure their actual capacitances by using your multimeter and record the values. Note that measuring capacitance with your multimeter should take a few seconds, so wait for the measurement to stabilize and then record the capacitance values. You will use these measured values in the rest of the experiment.
We want to study what happens when we charge two capacitors in series as shown in the first diagram below, then disconnect them from the circuit and connect them back in parallel as shown in the second diagram.
In the first circuit, they will get charged. But since their capacitances are not the same, the voltages across them will also be different. First calculate theoretically what those voltages would be.
Then build the circuit below but do not connect the power supply yet. You should be careful how you connect the electrolytic capacitors as they are polarized, which means they have + and – terminals. The – terminals are marked with a band that has a – sign on it. Make sure to connect them correctly in your circuit. Also make sure that the capacitors are discharged before you connect the power supply. You can discharge them by connecting their terminals together for a few seconds. After they are discharged, connect the power supply and measure the voltages across the capacitors. Do they agree with your theoretical predictions?
Now we want to disconnect the power supply and connect the capacitors in parallel as shown in the diagram below but without discharging them. They will keep the charge they collected in the first circuit, and that charge will get redistributed when you connect them in parallel.
Again, first calculate theoretically what the final voltage across them should be.
[Hint: Since the capacitors are connected in parallel in the second circuit, they will both have the same potential difference. Also since the charge on them can’t go anywhere else, if one of them loses some charge ΔQ (Q → Q-ΔQ) the other one will gain the same amount of charge (Q → Q+ΔQ). Keep those in mind and use the definition of capacitance to figure out the final voltage across them.]
Then connect them in parallel and measure the voltage. Does your measurement agree with your theoretical prediction?
Show your work and include pictures in your report.
Experiment 5: RC Circuits
In this experiment, you will study a discharging RC circuit. Build the circuit shown in the circuit diagram below by using a 10 kΩ resistor and the 2200 μF electrolytic capacitor included in your kit. Be careful about the polarity of the electrolytic capacitor. Its – terminal is marked with a band that has a – sign on it. Instead of using a switch, keep the wire disconnected.
In this circuit, when you close the switch (or connect the wire), the capacitor will very quickly charge, and the voltmeter will show 5 V. If you then open the switch (or disconnect the wire), you will measure the voltage on the capacitor as a function of time as it discharges over the 10 kΩ resistor. We know that the voltage should change with time as V(t) = V0 exp(-t/τ), where V0 is the initial voltage, and τ = R C is the time constant of the circuit.
Show that if you measure the voltage across the capacitor at two different times t1 and t2, then the time constant of the circuit can be found with τ = Δt / log(V1/V2), there V(t1,2) = V1,2,, and Δt = t1 – t2.
Use this method to determine the time constant of your RC circuit and compare it to the calculated value. You can use a Δt of up to 10 secs and start at a random time (not necessarily at t=0) shortly after you start discharging your capacitor. Include a picture of your setup.
Experiment 6: Puzzling behavior
In this experiment, you will build a very simple circuit that is made of two coils and explain your observation.
Now we’re going to build two overlapping coils. Start by wrapping one of the long jumper wires around a pencil. Then connect the wires to your breadboard. Then wrap another long jumper around the same part of the pencil so that the coils overlap.
Connect your multimeter to one of the coils and switch it to the frequency measurement setting marked with Hz/DUTY. This setting is used for measuring the frequency of an oscillating signal. We will connect the other coil directly to the 9V battery given in your kit. But we will only connect and disconnect it periodically and quickly as shown in the video for a few seconds. [WARNING: Do not keep the coil connected to the 9V battery for longer than a second. Since the wire has almost zero resistance, connecting the battery directly to a wire produces a large current and a lot of heat. You might end up burning your hand or start a fire.] Now although the multimeter is not directly connected to the battery, it looks like it detects and measures the frequency of the oscillating signal that we produce by periodically connecting and disconnecting the battery,
Try to build this circuit yourself, include a picture and explain how the multimeter can detect the oscillating signal