How can you tell if an object is charged? How can you tell if an object is positively or negatively charged? How can you tell if an electroscope is positively or negatively charged?
If you bring an object close to the knob of the electroscope and the two leaves of the electroscope move apart, your object is charged. If you bring an object close to the knob of the electroscope and nothing happens to the leaves of the electroscope, your object is not charged or is currently neutral.
The electroscope itself will be neutral. When you bring a charged object close, the electrons will start to move around and change their positions. If a positively charged object is brought close to the knob of the electroscope, the electrons would want to be close to it and since positives and negatives attract each other, and will move to the top (knob) of the electroscope. This will leave a positive charge in the leaves of the electroscope. Since like charges repel, the two leaves will move apart. If the object is negatively charged, the electrons will move away from the object near the knob of the electroscope and will move to the leaves of the electroscope. The leaves are left with a negative charge, and so the leaves will repel and move apart.
You can tell if an object is positively or negatively charged by looking at a Triboelectric Series Chart. It shows that if you rub an object from the top of the chart with an object from the bottom of the chart, the object from the top will lose its electrons to the object from the bottom of the chart. The object from the bottom of the chart will become negatively charged and the object from the top of the chart will become positively charged. The objects in the bottom of the chart have a greater electron affinity or ability to hold electrons than the objects from the top of the chart.
If you bring a positive object near the knob of the electroscope, and then touch the knob of the electroscope with your finger, you have charged the electroscope by induction. When you charge by induction the neutral object gains the opposite charge as to the charge of the object that was being used to induce a charge. So in this case, the electroscope (neutral object) will gain a negative charge.
Now if we rub two objects together and use the Triboelectric Series to see which one is positively charged and bring that object close to the knob of the electroscope and charge by induction, what will happen to the electrons inside of the electroscope? The electrons will move to the top of the electroscope leaving the leaves more positive. Since there are more electrons than protons in the electroscope because of induction, the leaves will be left with more protons and will move closer together because the force of repulsion is weak but will still repel. If you move the positively charged object away, the electrons will spread out evenly in the electroscope since there would no longer be a force of...