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5.2 Measurement of radiant intensity as a

function of the temperature of the fila-

ment



Connect the thermopile to the P3340 digital

multimeter (1002785).



Set up the Stefan-Boltzmann lamp in front

of the thermopile and connect up the DC

power supply and the two P1035 digital mul-

timeters (1002781).



Apply a voltage in steps of 1 V up to a max-

imum of 12 V, measure the lamp voltage U,

the lamp current I, and use the thermopile

to measure the radiant intensity  (5.3,

Tab. 2).

5.3 Evaluation



Calculate R = U/I (Tab. 2).



Now the values determined, T

be used along with the temperature coeffi-

cient

resistance

 = 4.4 · 10

to calculate the tempera-

-3

-1

ture of the filament by means of the follow-

ing formula (Tab. 2):











ref

















ref

, R

, R, can

ref

for

tungsten

ref

One possible alternative method for determin-

ing the temperature T of the filament is to calcu-

late the quotients R/R

Tab. 3 to find the temperature.

Note: In Table 3 the quotient R/R

for T

= 300 K and for T

ref

to determine the temperature more precisely by

interpolating between these two reference val-

ues to take account of the actual room temper-

ature.

Plot  as a function of T



Tab. 2: Values for the resistance R and the tempera-

ture T of the filament calculated from the

measured values for the lamp voltage U and

the lamp current I, as well as the radiated in-

tensity  measured with the thermopile

U / V

I / A

0.00369

0.006

1.0502

0.554

2.033

0.706

3.012

0.837

4.003

0.958

5.012

1.071

6.017

1.174

7.074

1.276

8.028

1.362

9.011

1.446

10.088

1.534

11.02

1.607

11.685

1.68

and then use Fig. 2 or

ref

is specified

ref

= 290 K. It is possible

ref

(Fig. 3).

 / V

R / Ω

T / K

0.615

328

1.896

854

0.0001

2.879

1259

0.0004

3.599

1554

0.0011

4.178

1792

0.0019

4.679

1998

0.0029

5.125

2181

0.0042

5.5434

2353

0.0058

5.894

2497

0.0072

6.232

2636

0.0088

6.576

2777

0.0106

6.8575

2893

0.0125

6.955

2933

0.0145