How does a phone stylus still register on a screen when something like an eraser, which feels somewhat similar, doesn’t?
What allows some materials to register on a screen, and others not to register?
In: Technology
Touch screens generally work due to “capacitance”. That is the ability for a material/object to store an electrical charge.
The human body is reasonably good at this, due mainly to containing a large amount of water. Water molecules are [slightly more positive on one end and more negative on the other.](https://s3.amazonaws.com/user-content.enotes.com/e9051bff4b4e7a03460d69f59ac430160eb764f6.png) If you expose them to an electrical field (a voltage), the water molecule will rotate a bit. In this way, it’s storing a bit of energy. If you remove the voltage, it will go back to moving around more freely.
Touch screens work by putting a tiny voltage on the screen (in many places, one after the other, very rapidly) and detecting if there’s a tiny current flow. If there is, something with capacitance has touched or come near the screen. Like a human finger.
But it doesn’t have to be the finger itself, it can be something electrically well connected to that finger. That will form a conductive path to the finger and it’s almost as good.
And that’s what a phone stylus does. It is conductive, and it therefore provides a “virtual finger” that increases the capacitance at the screen where it touches.
If a material is not very conductive, or not in electrical contact with something with high capacitance, it won’t register on the screen.
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