When you bring a positively charged rod next to the electroscope without touching it, the electroscope is neutrally charged, yet the leaves at the bottom of it repel each other. Why?
When a positively charged rod is brought near an electroscope without touching it, the leaves of the electroscope will repel each other because of the principle known as electrostatic induction.
To understand why this happens, you need to be familiar with the concept of charge polarization. When the positively charged rod is brought near the electroscope, the positive charge of the rod exerts a force on the electrons in the metal leaves, causing them to redistribute within the leaves. The electrons are repelled by the positively charged rod, so they move away from it.
As a result, the electrons on the near side of the leaves are repelled by the electrons in the rod and move towards the far side of the leaves, leaving the near side positively charged. Similarly, the far side of the leaves becomes negatively charged as electrons accumulate there due to the repulsion from the electrons in the rod.
This redistribution of charges in the leaves creates an electric field within the electroscope. Since like charges repel each other, the positive charges on the near side of the leaves repel each other, causing the leaves to spread apart.
It's important to note that the electroscope as a whole remains neutrally charged because no charge is added or removed from it. Instead, the charge within the electroscope is rearranged due to the presence of the positively charged rod nearby.
In summary, when a positively charged rod is brought near an electroscope without touching it, the leaves of the electroscope repel each other due to the redistribution of charges caused by the principle of electrostatic induction.