EPROM (Erasable Programmable Read-Only Memory) is a type of non-volatile memory that can be programmed and erased multiple times. It is commonly used in various electronic devices, such as microcontrollers and computer systems, to store small amounts of data that need to be retained even when power is turned off.

EPROM can be erased by using ultraviolet (UV) rays. Here's how it works:

1. Construction of EPROM:
- EPROM is made up of a grid of memory cells, where each cell consists of a transistor and a floating gate.
- The floating gate is insulated from the other components of the memory cell, allowing it to retain charge even when power is removed.

2. Programming EPROM:
- To program an EPROM, a higher voltage (typically 12V) is applied to the control gate of the transistor, allowing electrons to flow from the source to the floating gate.
- This process charges the floating gate, altering the threshold voltage of the transistor and storing a binary value (0 or 1) in the memory cell.

3. Erasing EPROM:
- When it comes to erasing the data stored in EPROM, UV rays are used.
- The EPROM chip has a small transparent window on top that allows UV rays to penetrate and reach the floating gates of the memory cells.
- The UV rays cause the charge trapped in the floating gates to dissipate, effectively erasing the stored data.
- The erasure process resets the threshold voltage of the transistors, making them ready for reprogramming.

4. UV erasure procedure:
- The EPROM chip is typically placed under a UV eraser, which contains a UV light source.
- The chip is exposed to the UV light for a specific duration, usually around 20 minutes, to ensure complete erasure of all memory cells.
- The UV light penetrates the transparent window and allows the trapped electrons in the floating gates to escape, returning the transistor's threshold voltage to its original state.

In conclusion, EPROM is erased using ultraviolet (UV) rays. The UV light penetrates the transparent window of the EPROM chip, causing the trapped charge in the floating gates to dissipate and resetting the memory cells for reprogramming.