3B Scientific Determination of Planck's Constant Apparatus User Manual
3B SCIENTIFIC® PHYSICS
Light emitting diodes for determining Planck’s constant (h)
8482460
Instruction sheet
07/06 SP
1 Sockets for LED’s (anode)
2 LEDs, blue to infrared
3 Socket for 100 series resistor
4 Series resistor on (rear of) cir-
cuit board 100
5 Socket for common cathode
1. Safety instructions
• When the diodes are brightly illuminated, avoid
looking directly at the radiating surface.
• Do not exceed the maximum current.
• Do not operate the diodes without the series
resistor.
• Do not allow any liquid to enter the equipment.
2. Description
The equipment is used to determine Planck’s constant
h by measuring the diffusion voltage of multicoloured
LEDs as a function of wavelength or frequency. It is
also possible to determine wavelengths by means of
lattice diffraction, as well as the relation between
luminous intensity and current. In addition, the
equipment can also be used to determine the current/voltage characteristic curves for the LEDs. The
circuit board is equipped with six LEDs in the colours
blue, green, yellow, and three different wavelengths
of red. The cathodes are lall connected to a common
rail. The resistor serves as a protection and should
always be connected in series when operating the
diodes.
1
⋅=⋅
3. Technical data
Operating voltage: 6 V DC
Maximum permissible
current: 20 mA, LED (infra-red)
100 mA
Diodes: 6 LEDs (blue, green, yellow,
and 3 different wavelengths
of red)
Series resistor: 100 Ohm, 1 W
Connections: 4-mm safety connectors
Dimensions: 115 mm x 115 mm
Weight: 120 g approx.
4. Sample experiments
In order to conduct the experiments, the following
apparatus is additionally required:
1 DC power supply unit,
0-30 V, stabilised: 8521145
1 Multimeter, Escola 10 8531160
1 Stand base 8611210
Experiment leads
4.1 Determining Planck’s constant (h)
• Connect the diodes individually via the resistance
to the voltage source. Make sure they are forward
biased.
• Switch on the power supply unit after setting it to
the minimum voltage.
• Gradually increase the voltage.
The diodes light up when the bias voltage U
connections 1 and 4) has been reached.
For a wavelength of 950 nm, the light emission can be
observed through the viewfinder of a digital camera.
4.2 Evaluation
• Calculate the frequency values from the wave-
lengths.
f = c/λ
• Calculate the values for energy.
E = e *10
• Based on the energy values in the E/f curve, calcu-
-19
·U
D ,
late the gradient of the curve.
• Derive the constant (Planck’s constant h) from
the gradient.
fhUe
D
λ (nm)
Colour
f in 10
f = c/ λ
14
Hz
UD in V
Measurements
E = e * UD in J*10
(e = 1.602*10
465 Blue 6.45 2.26 3.62
560 Green 5.36 1.72 2.76
585 Yellow 5.12 1.67 2.67
635 Light red 4.72 1.51 2.419
660 Dark red 4.54 1.44 2.307
950 Infra-red 3.15 1.0 1.6
(between
D
-19
-19
As)
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.
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