Can be part of the circuit Ohm's law. Used as an additional resistor to expand the range of volts. Used to measure unknown resistance. Used as electromotive force and internal resistance for measuring power supply. Used as a known resistor in the circuit to regulate the required current. Used for physical electricity experiment teaching. Type: Resistance Box Model Number: 15026 : ELECTRICAL color:Black Material:plastic size:16.5 x 12.5 x 6.4cm Package Contents: 1 x Resistance Box Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.