Planck's constant pack

This pack contains the Lascells Planck's constant apparatus, a ±12 V Smart Q Voltage sensor and a ±100 mA Smart Q Current sensor.

The Planck's constant apparatus is easy to use and will give very good approximations to Planck's constant. This apparatus provides an array of 7 clear LEDs with peak emission wavelengths in the range 430 to 950 nm (430, 505, 560, 615, 655, 850, 950). The controls allow each LED to be selected in turn and the applied voltage varied so its electrical characteristics may be investigated. 

The ±12 V Voltage and ±100 mA Current sensors (used with a data logger) are used to log the flow of current and therefore mark the start up voltage of the LED (so no visual observation of the LEDs is required). This data is used to create a graph of Energy vs. Wavelength, the slope of which is Planck's constant. 

Power can be supplied by the LAS0009 Battery pack/supply (with 3 x 1.5 V cells) or a smoothed 5 V DC power supply via 4 mm connecting leads.

The wavelengths marked are the LED manufacturers quoted wavelengths, students could examine the spectrum produced by each LED with the Data Harvest Spectrometer to get a more accurate value for wavelength

Supplied with a black observation tube (to help observe when light is just detected from one of the LEDs). 

Can also be used with voltage and current meters (current range 0 to 20 mA and voltage 0 to 5 V).

A 5 V battery eliminator can be connected to the external d.c. socket on the side of the apparatus (central pin = negative terminal).

If higher supply voltages are used the on-board potential divider would be able to apply voltages higher than 5 V to the LEDs and they could be damaged by excessive current