MORE APPLICATIONS

On this page you will frequently be graphing results in a Microsoft Excel chart. When you need to graph data, you will see a "Graph It" icon which you can click on to get to the excel chart. If you are using Netscape, you may have to right click on the icon, choose "Save Link As...", save the chart to your computer, and then open it with Excel.

RELATIONSHIP BETWEEN VOLTAGE AND RESISTANCE

If Ohm’s Law represents a mathematical relationship (V=IR) between the current (I), voltage (V) and resistance(R), for each of the following voltages V1 = 18 V and V = 36 V, how much current do you need to light the bulb? How would you control the amount of current? To answer the questions, use the given set up of the circuit below. Set up a chart like this one:

      
This way, you can record the different resistors that you are using, the voltage value and of course your calculated current. Notice that the amount of resistance provided by the resistor is represented by a number on it-likewise for each of the batteries (voltage shown on battery). After you’re done, graph your results by clicking on the graph icon.

1. What do you notice about the current?
2. When does the bulb blow up?
3. Why does the bulb blow up?
4. So what do you think the relationship between Voltage and Resistance is?
5. In which direction is the current flowing?

Now since you’ve played around a little with the circuit above, try and find out how Power required for the bulb and Current passing in the circuit relate to each other. Note that the Power on the bulb is given numerically and the unit of measurement for Power is Watts.

Series and parallel circuit

Series circuit

In the following you will notice that Voltage in the battery is a constant. Once you click on the switch, the current flows through the circuit. We know this because we can see the light bulbs light up. Try it on any of the circuits below.

Ok now, follow the procedures to discover more interesting things about the relationship between Voltage, Resistance and Current.

1. Make sure your switch is off (we don’t want to waste any of our batteries potential difference now do we J!   
2. For each different bulb, try different combinations and record the voltage, current and power. Chart examples are done for you with 1.0 ohm bulbs
3. Before you begin, clear all bulbs from the circuit by clicking and dragging each out of the circuit.
   • Place 1 ohm bulb and click switch, record results
   • Place 2 1 ohm bulbs, click switch and record results
   • Place 3 1 ohm bulbs, click switch and record results

To make things easier, you can draw up the following charts and register your findings.

SET A: For 1 ohm bulbs:

SET B: For various combinations:

Once you are done, graph your results for each set.

• What does the graph tell you?
• What do you notice about the relationship between Voltage, Current and Resistance?
• What happens to the resistance in this series circuit?
• Can you represent the total resistance by way of a mathematical equation?
  • If yes what is it?

Parallel circuit

1. Before you begin, clear all bulbs from the circuit by clicking and dragging each out of the circuit.
2. Make sure your switch is off (we don’t want to waste any of our batteries potential difference now do we J!
3. For each different bulb, try different combinations and record the voltage, current and power. Chart examples are done for you with 1.0 ohm bulbs
• Place 1 ohm bulb and click switch, record results
• Place 2 1 ohm bulbs, click switch and record results
• Place 3 1 ohm bulbs, click switch and record results
• Place 4 1 ohm bulbs, click switch and record results

To make things easier, you can draw up the following charts and register your findings.

parallel circuit simulation

These applets were written by Mihye Won - University of Illinois at Urbana-Champaign.
For more of Mihye's work click here:
http://www.students.uiuc.edu/~mihyewon/ci335/electricity/learning.html

SET A: For 1 ohm bulb:

SET B: For various combinations of 1 ohm bulb:

You can perform different sets for each of the different types of bulbs. Try doing all types of combinations. Once you are done, graph your results for each set.

• What does the graph tell you?
• What do you notice about the relationship between Voltage, Current and Resistance?
• What happens to the resistance in this parallel circuit?
• Can you represent the total resistance by way of a mathematical equation?
  • If yes what is it?

1. What would happen in the combinations for each of your series circuits above if you were to remove one bulb from anywhere in the circuit? (For example, will the other bulbs get brighter? Dimmer?  What will happen to the current?)  First try to predict what you will get by calculating your expected resistance, current and voltage using Ohm’s law and then, try it out on the circuit and see what you get!
2. What would happen in the combinations for each of your parallel circuit above if you were to remove one bulb from anywhere in the circuit?  (For example, will the other bulbs get brighter? Dimmer?  What will happen to the current?)  First try to predict what you will get buy calculating your expected resistance, current and voltage using Ohm’s law and then, try it out on the circuit and see what you get!
   

Experiments

Try this experiment in class or at home!