﻿ Work task - Voltamper characteristic of bulb
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## Voltamper characteristic of bulb

1. Measure the point-by-point dependence of the electric current (2.2 V/0.18 mA) on the connected voltage on the bulb.

2. Get the values obtained into the voltamper characteristic of the bulb. Determine the form of dependency with theory.

3. Calculate the static resistance values from the measured values and construct a graph of the DC resistance of the filament of the bulb at the supplied voltage.

4. In the graph, find the differential resistance values (using the tangent design) for the "cold" bulb and then for the filament filament lamp.

5. From the static resistance change, estimate the fiber temperature in individual cases - it is also possible to plot the dependence of the fiber temperature on the passing current (or the applied voltage or power).

#### Measurement procedure

1. We launch the remote experiment VeLMA - Voltamper characteristic of bulb

2. Use the slider (PC) or the buttons + a (tablet) to set different voltage values on the bulb.

3. At each moment we read the values of the electrical voltage and the electric current that are written in the table.

4. We measure the measured values continuously in the chart and, in the case of larger gaps between the measured dependencies, we measure the missing parts.

5. We watch a light bulb on the webcam and record the moment (voltage and current) when the thread is hot.

6. After the required number of measurement data (files and save all experimental values) remote role terminate.

7. We open the selected experimental data file in the spreadsheet (MS Excel, Oo Calc, Kingsoft Spreadsheets…).

8. We draw the electric current dependence on the connected electric voltage in the chart . We check the shape of the acquired dependence with the assumed shape.

9. Use the formula (1) to calculate the static resistance values for the different voltage of the measured interval. Dependence of the static resistance on the applied voltage draw into the graph.

10. In the area of the voltamper characterization that corresponds to the non-incandescent bulb, determine the direction of the tangent using a regression line. The regression line directive corresponds to the so-called differential (dynamic) bulb resistance - see formula (2).

11. Similarly, determine the differential resistance for the light bulb (preferably 2.2 V / 0.18 mA).

12. Using the formula for the temperature dependence of the electrical resistance of the metallic conductor R = R0 · [1 + α·(t – t0)], determine the approximate working temperature of the filament of the filament - assuming that the temperature of the fiber at the beginning of the experiment corresponds to the laboratory temperature t0 = 25 °C (Thermal coefficient of tensile strength of the tungsten fiber: α = 4,83·10–3 K–1).

 t  = t0 + R – R0 α·R0
##### Graph of temperature on current (voltage, power)

Using the formulas above, we can deduce some additional dependencies.

1. We plot the dependence of the approximate temperature of the fiber on the passing current by the bulb.

2. We will plot the dependence of the approximate temperature of the fiber on the applied voltage on the bulb.

3. We plot the dependence of the approximate temperature of the fiber on the bulb input (the product of voltage and current).

4. The obtained dependence (particularly from the point 15) compared to our assumption arising from the concept of the heat radiating bodies (eg. Stefan-Boltzmann law)