Question

Describe with the help of a diagram an instrument which can be used to detect a charged body.

Answer 1

Take an empty jam bottle. Take a piece of cardboard slightly bigger in size than the mouth of the bottle. Pierce a hole in it so that a metal paper clip could be inserted. Cut two strips of aluminium foil about \(4\) \(cm\) × \(1\) \(cm\) each. Hang them on the paper clip as shown. Insert the paper clip in the cardboard lid so that it is perpendicular to it. Charge a refill and touch it with the end of the paper clip. The aluminium foil strips receive the same charge from the charged refill through the paper clip. The strips carrying similar charges repel each other and they become wide open. Such a device can be used to detect whether an object is carrying charge or not. 
This device is known as electroscope. 

Answer 2

 Electroscope: An Instrument to Detect a Charged Body

An  electroscope is a simple device used to detect the presence and nature of electric charge on a body. Here is a detailed description of its components and working principle:

Components of an Electroscope:
1. Metal Rod: A vertical conducting rod that forms the central axis of the electroscope.
2. Metal Cap: Attached to the top of the metal rod, where a charged body can be brought near or touched.
3. Metal Leaves: Two thin metal foils (usually gold or aluminum) attached to the bottom of the metal rod, hanging freely.
4. Glass Enclosure: A container that encloses the metal rod and leaves, protecting them from air currents and external disturbances.

Working Principle of an Electroscope:

 Induction Process:
1. Approaching a Charged Object:
  - When a charged object (e.g., a negatively charged rod) is brought near the metal cap, it induces a redistribution of charges within the electroscope.
  - The electrons in the metal rod and leaves are repelled by the negatively charged rod, causing the leaves to acquire a similar charge (negative) and repel each other due to like charges repelling.
  - This causes the metal leaves to diverge.

Conduction Process:
2. Touching with a Charged Object:
  - When the charged object touches the metal cap, some of its charge is transferred to the electroscope.
  - This transferred charge causes the metal leaves to acquire the same type of charge (e.g., negative), leading to repulsion between the leaves, which results in them moving apart and staying apart.

 Detecting the Charge:
- Observation: The degree to which the metal leaves move apart can indicate the presence and magnitude of the charge. Greater separation indicates a larger charge.
- Nature of Charge: To determine whether the charge is positive or negative, one can use a known charged object to bring near the electroscope. If the leaves diverge further, the test charge is of the same type as the known charge; if they collapse, it is of the opposite type.

 Applications:
- Charge Detection: Used to detect the presence of an electric charge on an object.
- Charge Comparison: Can compare the relative magnitudes of charges on different objects.
- Nature of Charge: Helps in determining whether the charge on an object is positive or negative.

The electroscope is a fundamental tool in electrostatics, providing insights into the behavior of electric charges and helping to illustrate basic principles of electricity.