PC/CP200 Electronics Laboratory I

Other Components

Objectives

1. To understand the operation of a capacitor.
2. To understand the operation of a diode.

Equipment

• digital multimeter, bench power
• breadboard, bare DIP switch
• various resistors (1kΩ, 3.3kΩ, 10kΩ), capacitors (10μF, 100μF) ** note polarity **, diodes, LEDs
  

Procedure

1. Read Measuring Capacitance, and check the capacitance of a 100 μF capacitor. Use this for C₁ below.
   Demonstrate measuring capacitance to the lab instructor.
   
   
2. Construct the demonstration circuit shown below.
   
   

   Use a 5V supply and a standard LED.

   Let
   • R₁ = 3.3 kΩ
   • R₂ = 10 kΩ
   • C₁ = 100 μF

   Close and open the switch a number of times. Notice that you can see the time it takes to charge and discharge the capacitor because the LED will light up and dim slowly.

   You will be replacing various components in this circuit with ones of a different value. I want you to observe the change in charge and discharge times, if there is any.

   • replace R₁ with a 1 kΩ resistor. Does it charge faster, slower, or the same? Does it discharge faster, slower, or the same? Explain why.
   • keeping the modified circuit, replace C₁ with 10 μF capacitor. What happens to the charge and discharge times? Explain why.
   • Are the charge and discharge times a function of the resistance in the charge/discharge path or a function of the capacitance in the charge/discharge path?
     
     
   Demonstrate and explain operation of this circuit to the lab instructor.
   
   
3. Replace the capacitor in the previous circuit with two capacitors in series, as in the circuit shown below.
   
   

   Use a 5V supply and a standard LED.

   Let
   • R₁ = 3.3 kΩ
   • R₂ = 10 kΩ
   • C₁ = 10 μF
   • C₂ = 100 μF
   When you have two capacitors in series:
   • Does the order of the capacitors impact the performance of the circuit?
   • Does the smaller or larger capacitor dominate the response of the circuit?
   • A 10μF and 100μF capacitor in series provide a total capacitance of 9.1μF. What is the equation for combining capacitances in series? (If the answer is not obvious, do the next exercise and come back to this later.)
     
     
4. Replace the capacitor in the previous circuit with two capacitors in parallel, as in the circuit shown below.
   
   

   Use a 5V supply and a standard LED.

   Let
   • R₁ = 3.3 kΩ
   • R₂ = 10 kΩ
   • C₁ = 10 μF
   • C₂ = 100 μF
   When you have two capacitors in parallel:
   • Does the order of the capacitors impact the performance of the circuit?
   • Does the smaller or larger capacitor dominate the response of the circuit?
   • A 10uF and 100uF capacitor in parallel provide a total capacitance of 110uF. What is the equation for combining capacitances in parallel?
     
   Demonstrate and explain your results to the lab instructor.
   
   
5. Read Checking Diodes, and test the diode and the LED in forward and reverse directions. Could you tell which direction was forward biased by measurements alone? Could you tell an LED from a normal diode by measurements alone?
   Demonstrate and explain diode checking to the lab instructor.
   
   

6. Construct the demonstration circuit shown below, without the diode. Observe the brightness of the LED. Measure the voltage across the LED.

   

   Use a 5V supply and a standard LED.

   Let
   • R₁ = 3.3 kΩ
   • Add the diode to the circuit. Does the addition of the diode affect the brightness of the LED? Measure the voltage across the diode. Measure the voltage across the LED.
   • Replace the diode with another LED. Does the addition of a second LED affect the brightness of the original LED? Measure the voltage across each LED.
   • Explain your observations.
     
     
7. Construct the demonstration circuit shown below. The switch (use a piece of wire) can be at position A or at position B in the circuit. Observe the operation of the circuit with the switch at position A; then observe the operation of the circuit with the switch at position B. Explain the operation of the circuit.
   
   

   Use a 5V supply and two standard LEDs.

   Let
   • R₁ = 3.3 kΩ
   • C₁ = 100 μF
   Demonstrate and explain your results to the lab instructor.