Using a multimeter and photoresistor to measure light intensity of glow sticks in different temperatures of water

[deleted-814690]

For my science fair project, I am using this project from Science Buddies: https://www.sciencebuddies.org/science- ... #procedure.

Quick explanation of the project: We are putting glow sticks in different temperatures of water and measuring the light intensity using a photoresistor and a multimeter. Our independent variables are the different temperatures: 20°C (no water and control), 6°C (cold water), and 50°C (hot water). We are using the results after the glow stick had been in the temperature for 10 minutes. Our procedure was similar to the one Science Buddies provided.

Our hypothesis was as the water temperature increases. the light intensity of a glow stick will also increase. From doing our experiment, we can see that when we take the glow stick out of the jar, the hot water makes the glow stick brighter compared to the cold water.

We are confused on how to interpret the resistance reading from the multimeter. We used the kilo-ohms setting (kΩ).
Here is a sample from trial one of our experiment:
Glow stick in room temperature after 10 minutes: 24.5 kΩ
Glow stick in cold water after 10 minutes: 181.9 kΩ
Glow stick in hot water after 10 minutes: 27.5 kΩ

How do we interpret these results? How do we know which one had brighter light? Can you please explain the relationship between light intensity and resistance? Is the higher the number on the multimeter, the more resistance?

Thank you for your time

[norman40]

Hi katherine121,

When the multimeter is set to read resistance higher numbers mean more resistance. You might want to review the tutorial on measuring resistance:

https://www.sciencebuddies.org/science- ... resistance

The resistance of a photoresistor is very high in the dark and very low in bright light.

The data you posted indicate that the glow stick in cold water had less intense light (more resistance) than the room temperature or hot water glow sticks. Light intensity for the hot and room temperature glow sticks was similar (resistances nearly the same).

I hope this helps. Please post again if you have more questions.

A. Norman