When a positively charged rod touches the knob of an electroscope, it influences the behavior of the leaves. Here’s a detailed explanation:

Effect on the Electroscope
- When the positively charged rod comes into contact with the knob, it transfers positive charge to the electroscope.
- The electroscope consists of a metal conductor and two leaves that can move apart or come together based on the charge present.

Charging Process
- **Charge Transfer**: The positively charged rod causes electrons from the leaves to move towards the knob, leaving the leaves with an excess of positive charge.
- **Induction**: The presence of the positively charged rod induces a separation of charges within the electroscope, but the direct contact allows for a complete transfer.

Behavior of the Leaves
- **Repulsion**: Since both leaves now have a positive charge, they repel each other due to like charges.
- **Separation of Leaves**: As a result, the leaves will diverge and spread apart, indicating that the electroscope is charged.

Conclusion
- After the positively charged rod is removed, the leaves will remain apart until the charge dissipates through the environment or is neutralized.
- This experiment demonstrates the principles of static electricity and charge transfer, showing how objects can influence one another through direct contact.

Repelled away from each other, and hence, spread apart.