EP 11 Are we able to ‘see’ conductivity?
Objectives
In this lesson you will investigate how different materials and states of matter have different abilities to carry positive and negative charges. These charges attract each other. The attraction or movement of charged particles can be measured. We will start with the phenomenon of static electricity and then move to the conductivity of different substances when they are dissolved in water. You will then use the Boson Kit to measure the change in conductivity as more salt ions are added to water. This lesson will get you charged up!
Standards
NGSS - NEXT GENERATION SCIENCE STANDARDS
5-PS1-3 Matter and its Interactions Make observations and measurements to identify materials based on their properties.
Materials
Activity
Why does your hair “stick“ to the balloon?
●Have the students charge a balloon by rubbing it on their hair.
●Next, have them pull the balloon slowly away. Some of their hair should “stick“ to the balloon. If not, have them rub longer.
●After they have fun with this for a while, start a discussion about why this is happening. Someone may know it is because of static electricity but can they explain how static electricity works?
Explore
To measure the number of ions in the saltwater solution, we will be using the soil moisture sensor in the Boson Kit. The soil moisture sensor works by putting opposite charges on the two prongs (electrodes) of the device. The soil moisture sensor is an analog voltage sensor that can be used to measure a continuous spectrum of different conductivities.
Setup:
1.Connect the Battery Holder and two Module Cables to the Main Board.
2.Connect the OLED Module to the output side of the Main Board with a Module Cable.
3. Connect the Soil Moisture Sensor to the input side of the Main Board with a Module Cable.
4. Attach the Soil Moisture Sensor to the Cup with the Module Velcro.
5. Add the Distilled Water to the Cup. Fill the Cup so the water covers the bottom half of the legs of the Soil Moisture Sensor.
6.Turn on the OLED and turn it to the analog screen.
Experiment
1.Add scoops of Salt to the Distilled Water. Record the analog reading, which is the voltage reading.
2.Repeat Step 1 and gather data.
Data Record
Copy the Data Table below into your notebook.
Explain
Data Analysis:
Have students graph the results. We recommend students make the graphs by hand, but you could also use free software like Google Sheets.
Students can make a line of best fit and find the linear equation. This will allow them to determine the number of scoops in a solution of unknown concentration.
They use the conductivity meter to determine the voltage and then plug it into the equation as the y- value. Then they can then determine the amount of salt in the solution by solving for x.
Students test a solution’s voltage and get 730 volts. By looking at their graph they can determine this is about 3.7 scoops of salt.
Elaborate
Conductivity and the Flow of Ions
Ions = Charged Particles
Charged particles are called ions. Matter can be charged do to some change like the rubbing with the balloon. Other materials or matter innately carries a charge with it. The salt used in the Experiment is a material that carries a charge with it innately.
Conductivity = how much a material allows ions to flow through it
Ions(+/-) are attracted to their opposites. Ions attempt to move towards each other. The flow of ions to different places depends on the material they are in or the material the ions come into contact with. Some materials allow ions to move more freely while other materials resist that flow.
Voltage = how many negative charges “want” positive charges
Ions are charged and “want” their opposite. When a positive charge is near a negative charge, they will attract. This causes them to flow or move towards each other. We can measure the flow of ions. A common way of doing this is to measure the voltage. Voltage is simply a measurement of how many negative charges “want” to combine with positive charges. The conductivity meter we build in Experiment measures voltage or the flow of charged particles.
To be “charged up” means to separate positive from negative charges
In Activity, we get charged particles to separate by using friction. We prepare the balloon by rubbing it on our hair. Once the balloon is positively charged it is “looking for“ some negative charges.
Oppositely Charged Particles Attract
In Activity, the balloon was able to find negative charges in our hair so they were attracted to each other.
Evaluate
Consider the following questions:
1.If we rub a balloon on our hair and then place it near a thin stream of water, what will happen? And why is this happening?
2.Can you explain the data line graph in the experimental results from a micro perspective?
