Planck's constant apparatus

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.  

A black tube (supplied) is used to help observe when light is just detected from one of the LEDs. 

Obtain crisp results by using a data logger with a ±12 V Voltage and ±100 mA Current sensor. The logged flow of current will 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. See the Planck's constant pack. 

Power can be supplied by using 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.  

Can 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.