Lab Log

Week 7

Preliminary Set-up

Verified that the circuit is working

Week 8

Set-up

Set-up used to collect results for 5mm Red LED.

Raw Data

For 5mm Red LED,

R = 10kΩ

R = 100kΩ

R = 1MΩ

Remarks:

- At low resistance (10kΩ), the voltage across the resistor is too low to make inferences on the photodiode performance. However, it is noted that the frequency of the light source can still be determined.

- As the resistance is increased (100kΩ), a reasonable performance of the photodiode can be observed. We can determine the frequency of the light source and the rise time of the signal. The rise time is estimated to be around 0.3ms and it is closely related to the wavelength sensitivity of the photodiode. We can expect the rise time to stay constant for a given wavelength of the light source.

- With high resistance (1MΩ), the voltage measured is larger and hence the percentage uncertainty associated with the measurement is lower. However, a higher resistance imposes an upper limit on the frequency of the light source. It appears that blinking is faster than the response speed of the LED.

- Based on these results, the response of the photodiode for Red light is in the kilohertz region (between 1kHz to 10kHz) with a rise time of approximately 0.24ms.