3B Scientific Bolometer User Manual

3B SCIENTIFIC

Instruction sheet

07/08 ALF

®

PHYSICS

Bolometer U8461300

1 Hole for thermometer
2 Cardboard tube
3 End-plate

1. Description

A bolometer is used for measuring the heat radiation
from the sun.

The instrument consists of a solid aluminium
cylinder with a blackened end surface inside a
cardboard tube, which is blackened on its inner
surface and has two plastic end-plates. A hole is
provided in the tube and the cylinder for inserting a
thermometer.

The blackened surface of the aluminium cylinder
prevents reflection of the incoming heat radiation,
and a blackened cardboard tube screens the cylinder
from ambient background radiation.

2. Technical data

Aluminium cylinder: ≈ 30 mm × 40 mm Ø

Cardboard tube: ≈ 195 mm × 50 mm Ø
Weight: 350 g approx.

3. Sample experiments

To carry out the experiments the following
equipment is required in addition:

1 Thermometer +10 ... +30 °C U8451700

1 Tripod stand, 150 mm U13270

1 Stand rod, 470 mm U15002

1 Universal jaw clamp U13261

1 Universal clamp U13255

1 Digital stopwatch U11902

1 Set of Vernier callipers, 150 mm U10071

1 Electronic scale, 2500 g U42058

1 Pipette dropper

3.1 Measuring the quantity of heat transferred to
an aluminium body by solar radiation

Heat from the sun is transmitted to the earth by
thermal radiation. The intensity of the thermal
radiation depends on the position of the sun above
the horizon and the clarity of the atmosphere. The
earth’s atmosphere “swallows up” a fraction of the
solar radiation. That fraction may be smaller
according to how clear the weather is and how high
the sun is in the sky.

1

•

A

⋅

=

Set up the bolometer as shown in Figure 1, using
the stand, rod and clamps.

• Adjust the bolometer so that the sunlight shines

exactly along its axis. The shadow of the front
end-plate should then fall exactly onto the rear
end-plate.

• Before inserting the thermometer into the hole

in the aluminium cylinder, put in a few drops of
water to improve the transfer of heat.

• Insert the thermometer into the hole, read the

initial temperature, and record it in a table.

• In a series of measurements over a period of 10

minutes, read the temperature at intervals of 60
seconds and record the values.

• Remove the rear end-plate, unscrew the

aluminium cylinder, and determine its mass m
by weighing.

• Using the callipers, measure the diameter d of

the blackened surface and calculate the area A.

• Plot a graph of temperature against time to

show the heating-up of the aluminium cylinder.
Draw a line of best fit through the data points.

The temperature rise per minute, ΔT, is obtained
from the gradient of the line.

The quantity of heat Q received by the blackened

Air is a poor conductor of heat, and therefore
thermal conduction makes only a very small
contribution in this experiment. Furthermore, as the
heated air near the lamp flows upward and not
towards the “black body”, thermal convection also
makes no significant contribution to the heating of
the aluminium cylinder.

• Screw the filament lamp into the lamp socket

and connect to the power supply.

• Remove the cardboard tube and support the

aluminium cylinder with one end-plate using a
stand and clamp (Fig. 2).

• Position the aluminium cylinder so that its

distance l from the lamp filament is about 4 cm.

• Determine the quantity of heat per minute and

the radiation power per unit area in the same
way as in Experiment 3.1.

If the lamp filament is regarded as a point source of
radiation, the total radiation power S
by the lamp is the amount received by a sphere of
radius r = l. Therefore it is the product of the
calculated radiation power per unit area, S, and the
surface area of the sphere A

SAS

G

0

:

O

surface of the aluminium cylinder in one minute can
be calculated from the temperature rise per minute

ΔT, the mass m of the cylinder, and the specific heat
capacity of aluminium

TmcQ

Δ⋅⋅= (1)

Al

c :

Al

The specific heat capacity of aluminium is

J

896c

=

Al

• Using Equation 2, calculate the radiation power

per unit area (heat input per cm

Q

(2)

S =

3.2 Measuring the radiation power of a filament

.

°

Ckg

⋅

2

per minute).

Fig. 1 Measuring the radiation power of the sun

lamp

Additional equipment needed:

1 E14 lamp socket U8495320

1 Filament lamp 12 V, 25 W, type E14 as sold for

°C

domestic use

1 Transformer with rectifier (230 V, 50/60 Hz)
U33300-230
or
1 Transformer with rectifier (115 V, 50/60 Hz)
U33300-115

Experiment leads

Fig. 2 Measuring the radiation power of a filament lamp

that is emitted

G

°

C

Elwe Didactic GmbH • Steinfelsstr. 6 • 08248 Klingenthal • Germany • www.elwedidactic.com

3B Scientific GmbH • Rudorffweg 8 • 21031 Hamburg • Germany • www.3bscientific.com

Subject to technical amendments

© Copyright 2008 3B Scientific GmbH