An electroscope can be used to get an idea of how much electrical charge is on an object. It can't tell you if an object is negatively charged or positively charged, or give you a numerical value for quantity of charge but it will tell you if it is charged. If you have two charged objects, it may tell you if one is more charged than the other, based on how much the "leaves" in the electroscope move apart. The video below has an example of this.

The parts of an electroscope

Here's how it works...

Initially there are plenty of both negatively charged electrons (-) and positively charged protons (+) on the terminal. But the vinyl record has far more negative electrons than positive protons so we say it is negatively charged. When the negative vinyl is moved close to the terminal, the electrons on the vinyl repel the electrons on the terminal. This is because like charges repel each other. In this case negative is repelling negative. This leaves mostly positive protons on the terminal while the negative electrons are repelled down the wire and to the aluminium foil leaves. The leaves are free to move around a bit and since they are both negatively charged, they repel each other. That's how we know that the vinyl record is charged. If the vinyl record had an equal number of positive and negative charges then this would not happen.

As you can see, an electroscope is a quick and easy DIY project that can be made at home with household parts. The leaves in the above one are made with aluminium foil from the kitchen, the plastic top is cut from the plastic cover from a plastic container. A key point is that the terminal must be electrically connected to the leaves. In this case the terminal is a part of the wire that extends down into the glass jar, and that wire forms a hook which the leaves hang from.

The following is a video giving a demonstration of all this.

The following is a video demonstrating how to inductively charge an electroscope such that the electroscope will keep its charge even after you move the charged object away from the terminal.