Lab 5 Lab Circuit-Capacitors XXXXXXXXXXName _____________________
Lab Goal: To understanding what Parallel Plate Capacitors are and how they function in a circuit. Continue using electronic kits.
Background
Capacitors: From the beginning
This is Important because a capacitor is a circuit element and it is important to know how this element is used to control electrons to make them do what you want.
Chap 20 – Charges, Force, Fields
After exploring point charges we explored a uniform E field. This was generated from parallel metal electrodes (conductor plates) Parallel Plate Capacitor. Parallel Plate Capacitors are used to learn about electricity because they produce a uniform electric field and the focus will be on the grand variables instead of boundary conditions unlike in the cases of point charges or charged spheres.
Horizontal E field components cancel leaving only the vertical components of the E field.
Result is a uniform Electric Field.
Where Q is the charge on the plates, A is the area of the plates and is the permittivity constant.
Permittivity means the ability of a substance to store electric energy.
is the permittivity of air and is
If the material between the plates is not air the permittivity ∈ is provided in a table built from experiments. This type of parallel plate capacitor is called a dielectric. Having a material other than air between the plates will affect the Electric field that is produced by the charge plates.
Chapter 21-Potential: Develop an understanding of Uelec and Potential of a Parallel Plate
Capacitor:
XXXXXXXXXXMost General Information:
From the force side of analysis
F = q E E = XXXXXXXXXXwhere E is a result of the source charge(s) and q is the test charge
From the energy side of analysis:
Uelec = q V V = XXXXXXXXXXwhere Uelec is a result of the source charge(s) and q is the test charge
Capacitor specific:
From derivation of Work and conservation of Energy:
– ∆Uelec = W = q(–E) ∆x
Simplifying:
∆Uelec = q E ∆x
and connecting electric potentional energy to electric potential:
∆V = = E ∆x
The potential difference inside a parallel plate capacitor is
∆Vx = E ∆x
If d is the separation distance of the charged plates, then the potential difference of the parallel plate capacitor
∆VC = E d
Recall that the magnitude of a parallel plate capacitor is
E = ∆VC = d
Rea
anging terms: ∆VC = = where C is called the Capacitance.
The direct relation of measureable potential to measureable charge is
∆VC = or Q = C ∆VC
_______________________________________________________________________
Objectives: In this lab, you will
Part 1
· Explore a parallel Plate Capacitor
· Explore the variables of this circuit element (ie. charge, potential energy, charge flow , etc)
Part 2
· Verify a few equations developed in lecture and apply to a real electrical creature.
Part 3
· Work with e-kit and accompanying manual
Connect to PhET and
ing up Capacitor Lab: Basics:
https:
phet.colorado.edu/sims/html/capacitor-lab-basics/latest/capacitor-lab-basics_en.html
Part 1: Getting to know a Parallel Plate Capacitor.
XXXXXXXXXXFor a warm up you will determine the capacitance of the capacitor in the PhET simulation.
A. Charging capacitor
Procedure:
2. Click on Capacitance icon.
3. Connect the capacitor across the battery.
4. All the parameters (plate charges, bargraph, electric field and cu
ent direction) must be selected as
shown below
5. Connect the voltmeter across the capacitor and record your observations below:
What happens to the charge on the plates?
Charge on the upper plate
Charge on the lower plate
Direction of electric field
Potential difference across the capacitor
Capacitance
Increase the battery voltage to +1.5V.
Decrease the battery voltage to
-1.5V .
Keep the battery voltage at 1.5 V and increase the plate area
Keep the battery voltage at 1.5 V and decrease the plate area
Keep the battery voltage at 1.5 V and decrease the separation
Keep the battery voltage at 1.5 V and decrease the separation
B. Discharging capacitor
Procedure:
1. Click on the Light Bulb icon on the bottom of the PhET screen.
2. Make sure the capacitor is connected to the battery and its voltage is 1.5V.
3. Connect the voltmeter across the capacitor.
4. All the parameters must be selected as shown below:
5. Disconnectthechargedcapacitorfrombatteryandconnectitacrossthebulbandrecordyour observations in the table below:
What happens to the following?
Increases/Decreases/stays constant
Charge on the plates
Potential difference across the capacitor
Capacitance
Energy stored in capacitor
Glow of the bulb
Conclusion:
1. How can we charge a capacitor?
2. How can we discharge a capacitor?
3. What are the ways to increasing the capacitance of a capacitor?
4. What would be the potential difference of the capacitor if it is connected to a battery of 3V?
5. On increasing the voltage of the battery what happens to the charge on the plates of the capacitor?
Part 2. Capacitor’s linear relationship between Q and V
Purpose:
To evaluate the relationship between the charge held in a capacitor and the potential difference (voltage) across the capacitor’s plates.
Procedure :
1. Go to the simulation website above. Select the “Capacitance” mode. Grab the voltmeter tool and place the red end to the top plate and the black end to the bottom plate as shown below:
The figure above shows the set up for the simulation
2. Check the “top plate charge” option on the menu at the top.
i. Record the value you see for the charge of the top plate and for the voltage.
ii. Move the slider on the battery upwards until the voltage increases by 0.15V and record the
XXXXXXXXXXvalue you see for the charge of the top plate and for the voltage.
iii. Move the slider up, increasing the voltage by 0.1V, and record the charge and voltage values
iv. Repeat step iii until the voltage value is 0.95 V.
3. Make observations as you do the steps in number 2.
i. What did you observe happening on the metal plates as the voltage increased? Explain in terms
XXXXXXXXXXof charges. Is the effect on the plates still there some time after you finish increasing the voltage?
ii. What happens on the wires as the voltage increases? Does this effect on the wire continue
XXXXXXXXXXsometime after you are finished increasing the voltage? Explain.
You can record your data in a table below.
Voltage (x-axis)
Charge (y-axis)
Description-charges
Description-wires
0
.15
.25
.35
.45
.55
.65
.75
.85
.95
1.05
1.15
4. Using the table values for V and Charge to make a graph, and apply a curve fit. In order to identify what type of curve fit to use, Interpret your data using the equation:
Q=CΔV
where Q is the charge on the capacitor, C is capacitance, and ΔV is the voltage. Insert you plot below.
5. Use the result from your curve fit to find a value for your measured capacitance. Explain how you identified your value for capacitance from the curve fit.
6. Note that the capacitance of the capacitor is shown on the top bar of the simulation. This value is our expected value for capacitance. Calculate the percent difference between these two values of capacitance.
Part 3: Familiarize yourself with actual circuits.
Procedure: For the following Manual chapters, follow instructions and work the circuit.
XXXXXXXXXXFor each chapter setup, draw a circuit picture.
XXXXXXXXXXNOTE that CHAPTER 5 has circuit element diagrams to use.
XXXXXXXXXXNOTE that CHAPTER 3 shows how to use an ammete
XXXXXXXXXXNOTE that CHAPTER 8 shows how to use a voltmete
Chapters to explore
1. basic circuit construction
“just do it” -> follow instructions and get the skill for building a circuit.
2. build a series and a parallel circuit
a. build the circuits (Fig 2.1 and 2.2)
b. draw the circuit diagrams
c. describe the circuits build: what is different and what is similar.
After learning how