# Physics307L F07:People/Lancaster/Notebook/070924

--Michael T. Lancaster 16:30, 24 September 2007 (EDT)Speed of Light

# Speed of Light

## Getting Familiar with the equipment.

The old lab manual has a solid account of how to set up this lab. Now that the safety protocols have been followed. The PMT tube has a negative voltage of 1900V being applied to it. While the pulse LED has a positive voltage of 190V being applied. According to to Brian and Antonio this will effect the pulsing frequency of the LED. I wonder why?

--Michael T. Lancaster 16:40, 24 September 2007 (EDT)

## Taking Measurements

The most crucial aspect of taking the time delay measurements is the time walk phenomenon. The old lab manual explains this very well I think, the graphic especially is helpful. Since there is a second output on the PMT it is fairly straight forward to connect this to one of the channels on the O-scope and maintain a consistent output voltage on the PMT by rotating the polarizers relative to each other.

--Michael T. Lancaster 18:59, 24 September 2007 (EDT)

The PMT output voltage that I will try and maintain is 696mV.

Voltage(V) Initial distance (cm)

8.6V 0 (starting point) 8.6V 4 8.6V 8

### Attempt 2

--Michael T. Lancaster 19:16, 24 September 2007 (EDT): Decided to reduce delay and change TAC scale to 50 ns. No delay box is all set to off, delay. Using 800 mV +/- 008 mV as the peak (negative) PMT for reference. Using the "measure" function to read the PMT value as well as the TAC voltage. When reading TAC voltage, using 128 averages.

```Voltage (V)     Distance (cm)
----------       ------------
5.04 +/- 0.04              8 (aberration?)
5.08 +/- 0.04              14
5.04 +/- 0.04              20
4.96 +/- 0.04              26
4.88 +/- 0.04              32
4.88 +/- 0.04              38
4.84 +/- 0.04              44
```
```quick analysis: deltaV = .24 V , deltaD = 0.3 m <br>
0.24 V * 50 ns / 10 V = 1.2 ns<br>
speed = 0.3 m / (1.2 E-9 s) pretty close!
```