Overview
Capacitance Simulation
- Select the Capacitance SimulationLinks to an external site.
- Connect the voltmeter (in the right box) to the capacitor to be able to measure the voltage.
- Using the battery, set the voltage ∆V to a value of your choice.
- Choose a new value for the separation between the electrodes (capacitor plates) and their area.
- Check the boxes in the top left bar to be able to read the values of C, Q, and U
a. Using the formulas from the course (Week 3 Module), calculate the values of C, Q, and U (energy). Show the formulas you used.
b. How do your values compare with the values given in the top bar?
c. What happens if you switch the battery from +V to -V ?
d. How does the Capacitance change if you decrease the separation between the plates?
e. How does the Capacitance change if you increase the area of the plates?
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Light Bulb Simulation
- Run the Light Bulb SimulationLinks to an external site.
- Charge the capacitor at a voltage ∆V of your choice.
a. Do the charges remain on the electrodes when you disconnect the capacitor from the battery (middle position for the switch)? Does that mean that the energy given by the battery to the capacitor is actually stored in the capacitor?
b. Connect the charged capacitor to the light bulb. What happens to the energy of the capacitor? (The light bulb can be considered as a simple resistor and we will assume that its resistance is constant).
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Light Bulb Simulation
- The phenomenon observed with the capacitor and light bulb (resistor) is transient: It only lasts a few seconds during which the energy stored in the capacitor decreases to 0.
- We know that (Week 5, Pages on RC circuits) :
𝑄(𝑡)=𝑄(0)𝑒−𝑡𝑅𝐶
𝑈(𝑡)=𝑈(0)𝑒−2𝑡𝑅𝐶
- Here this means that there is a characteristic time (RC) for the charge and the energy to decrease in the circuit, and that this time depends on resistance (R) and capacitance (C).
- Choose a separation and a plate area that set a large value for C.
- Charge successively the capacitor at 0.5V, 1.0V, and 1.5V. Using a stopwatch or your phone, measure the time it takes for the energy to be divided by 4 once the capacitor is connected to the light bulb.
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Flag question: Question 4Question 46 pts
Light Bulb Simulation
a. Are your time measurements compatible with the equations for Q(t) and U(t)? Explain why or why not.
You don't need to calculate the values, just describe what the trend of your measurments looks like.
b. From the equations, what are the values of Q(t) and U(t) at time t = 0 s?
You don't need to put in any numbers for Q, U, R, C. Just write what happens in terms of the equation.
c. From the equations, what are the values of Q(t) and U(t) as time t ⟶∞ (infinity)?
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