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Chapter Twelve Problems

1. What is the relationship between voltage and current?

 

What role does resistance play between voltage and current?

 

If the voltage impressed on a circuit is held constant while the resistance doubles, what happens to the current? Explain why.

 

If the voltage is cut in half while the resistance remains the same, what happens to the current?

 

If you wanted to have the same current, how would you have to change the resistance from the last question?

 

Does voltage flow through a circuit, or is voltage established across a circuit? (Think about the waterfall analogy).

 

Does current flow through a circuit, or is it established across a circuit? (Again the waterfall analogy).

 

 

2. High voltage by itself is not damaging. What determines the danger?

 

 

Use Ohm's Law: V = IR for the following:

The resistance of a circuit is 10 ohms. Find the current if the voltage is 120 Volts. (I = 12 A)

 

 

The current of a circuit is 5 Amps. Find the resistance if the voltage is 130 Volts. (R = 26 ohms)

 

 

The current of a circuit is 2 Amps. Find the voltage if the resistance is 25 Ohms. (V = 50 V)

 

 

3. Which is more dangerous: wet skin or dry skin when touching a voltage? Explain.

 

 

If your resistance is 5,000 Ohms, find the current through you if you touch 120 Volts. (I .024A)

 

 

4. For the given circuit:


Find the following:

  • Total Resistance (Reduced Circuit):

     

     

  • Total Current:

     

     

  • Voltage Drops:

     

     

    State Kircholff's First Rule:

     

     

    For the given circuit:


    Find the following:

  • Total Resistance (Reduced Circuit):

     

     

  • Total Current:

     

     

  • Voltage Drops:

     

     

    5. For the given circuit:


    Find the following:

  • Total Resistance (Reduced Circuit):

     

     

  • Total Current:

     

     

  • Current paths:

     

     

     

     

  • Voltage Drops:

     

     

     

     

    State Kircholff's Second Rule:

     

     

    6. For the given circuit:


    Find the following:

  • Total Resistance (7.1 Ohms):

     

     

     

     

     

     

  • Total Current (2.8 A):

     

     

  • Current paths (I = 1.3 A; 1.5 A; 1.0 A; .50 A):

     

     

     

     

  • Voltage Drops:

     

     

     

     

    7. For the given circuit:


    Find the following:

  • Total Resistance (10.7 Ohms):

     

     

     

     

     

     

     

     

     

     

  • Total Current (1.9 A):

     

     

  • Current paths (I = 1.1 A; .80 A; .53 A; .27 A):

     

     

     

     

  • Voltage Drops:

     

     

     

     

    8. For the given circuit:


    Find the following:

  • Total Resistance (22.3 Ohms):

     

     

     

     

     

     

     

     

     

     

     

     

     

     

  • Total Current (2.24 A):

     

     

  • Current paths (I = 1.63 A; .610 A; .359 A; .251 A; .114 A; .137 A):

     

     

     

     

  • Voltage Drops:

     

     

     

     

    9. For the given circuit:


    Find the following:

  • Total capacitance (3.33 microfarads):

     

     

  • The time it takes the capacitors to reach 63 percent capacity. (.00010 seconds)

     

     

  • What would you have to change to make the time to charge up longer? Why?

     

     

  • How does adding capacitors in series compare to adding resistors in series?

     

     

  • How does the total capacitance for capacitors in series compare to the individual capacitors that make up that series?

     

     

    Explain why you think a large voltage would actually result in a smaller capacitance. (Remember in the equation (C = Q/v) voltage and capacitance has an inverse relationship.

     

     

    How does that fact agree with the distance between the plates? In other words, we established in class that farther apart plates result in a smaller capacitance. How does the distance between the plates relate to the voltage (or potential difference) between them?

     

     

    10. For the given circuit:


    Find the following:

  • Total capacitance (15 microfarads):

     

     

  • The time it takes the capacitors to reach 63 percent capacity. (.00045 seconds)

     

     

  • Why is the time for this circuit longer than the circuit in problem 9?

     

     

  • How does adding capacitors in parallel compare to adding resistors in parallel?

     

     

  • How does the total capacitance for capacitors in parallel compare to the individual capacitors that make up that series?

     

     

    How is that different for resistors?