A diode is a device which allows current flow through only one direction. That is the current should always flow from the Anode to cathode. The cathode terminal can be identified by using a grey bar as shown in the picture above.

For 1N4002 Diode, the maximum current carrying capacity is 1A it withstand peaks up to 30A. Hence we can use this in circuits that are designed for less than 1A. The reverse current is 5uA which is negligible. It can withstand reverse voltage peak up to 100V.

Features:

• Diffused Junction
• High Current Capability and Low Forward Voltage Drop
• Surge Overload Rating to 30A Peak
• Low Reverse Leakage Current
• Lead Free Finish, RoHS Compliant (Note 3)

Mechanical Data:

• Case: DO-41  Case Material: Molded Plastic. UL Flammability Classification Rating 94V-0
• Moisture Sensitivity: Level 1 per J-STD-020D
• Terminals: Finish - Bright Tin. Plated Leads Solderable per MIL-STD-202, Method 208
• Polarity: Cathode Band
• Ordering Information: See Page 2
• Marking: Type Number
• Weight: 0.30 grams (Approximate)

Datasheet: https://components101.com/asset/sites/default/files/component_datasheet/1N4002 Diode Datasheet.pdf