Features Lightweight and portable, the electromagnetic induction spiral coil specializes in electromagnetic induction phenomena, which is convenient to carry and use. Easy to use, it can be used with bar magnets, ammeters, sliding varistors and other instruments. Physics laboratory equipment auxiliary tools make physics experiment learning more efficient. Rugged and durable, constructed of enameled copper, wear resistant, not easy to be damaged, and long service life. It is designed to demonstrate electromagnetic induction and verify Lenz's law for students. It is an ideal choice for physics teaching. Specification:Item Type: Electromagnetic Induction Coil Material: PVC+Brass Purpose: Middle and high school physics experiment Applicable Experiments: Study electromagnetic induction, verify Lenz's law, study magnetic induction phenomenon The outer diameter of the hole at the bottom of the original coil is: Approx. 22±1mm / 0.9±0.04in The inner diameter of the hole at the bottom of the original coil is: Approx. 13±0.5mm / 0.5±0.02in The height of the round hole at the bottom of the original coil: Approx. 60mm / 2.4in The diameter of the hole at the bottom of the secondary coil is: Approx. 35±1mm / 1.4±0.04in The inner diameter of the circular hole at the bottom of the secondary coil is: Approx. 49±1mm / 1.9±0.04in The height of the round hole at the bottom of the secondary coil: Approx. 80mm / 3.1in Soft Core Length: Approx. 85mm / 3.3in Package List:1 x Primary Coil A1 x Secondary Coil B1 x Soft Iron Core C Note:1. Since the DC resistance of the original coil is very small, the current can not be too large, the power‑on time should not be too long, and the power supply voltage should not exceed DC4V.2. Pay attention to protect the plastic frame, and don't let it subject to strong collision or fall on the ground.3. After the instrument is used, it should be placed in a clean, dry and ventilated place without corrosive gas.4.Please note that the new type and old type of this product will be sent randomly, and make sure you will not mind before ordering. Package List 1 x Primary Coil A 1 x Secondary Coil B 1 x Soft Iron Core C