CHARGING BY ELECTROSTATIC INDUCTION

In the 18ᵗʰ century, British scientist John Canton and Swedish professor John Carl Wicke discovered the phenomenon of Electrostatic Induction.

When we bring a charged body near an uncharged object, equal and opposite charges are induced on the near-surface of the uncharged object. This phenomenon is called Electrostatic Induction. 

Charged objects have electrostatic fields around them, and when we bring an uncharged object near a charged object, then the electrostatic field interacts with the charges present on the surface of the uncharged object by attracting opposite charges and repelling like charges. 

Due to this phenomenon, we could charge an uncharged object without touching them directly. 

When the charge is induced in an uncharged body, the net charge on the body is zero. Since the body isn’t losing or gaining any charge, the charges are redistributing themselves due to the interaction with the nearby charges.

Some examples of Electrostatic Induction

• Electrostatic Induction between the charged and uncharged sphere

If we give a positive charge to a conducting sphere and then bring it close to the uncharged conducting sphere, then the negative charge is induced on the near-surface of the same magnitude. And the positive charge is induced in the away surface of the uncharged sphere.

• Electrostatic Induction between glass rod and electroscope

If we bring a charged glass rod near the metallic plates of an electroscope, then the charges on the metallic plates redistribute themselves. Due to which metallic plates diverge.

The formula for induced charge 

If we charge a body with Q, and then we bring it close to an uncharged body. Then the charge is induced on an uncharged object say q, then q is related to Q as:

q = Q (K-1)/K

Where K= dielectric constant of the medium 

Applications of Electrostatic Induction

• Van de Graaff generator

The Van de Graaff generator works on the principle of static electricity.

This generator is used to produce a high voltage of order 10⁶ V.

Its components consist of a metallic comb, motor-driven pulley, insulating belt, and metallic sphere. 

The insulating belt, which is kept moving by a motor, carries the charges from the grounded metallic comb to the metallic sphere. Due to this, charges keep on accumulating in the metallic sphere, and we get a voltage of the order 10⁶ V.

• Capacitor

In a capacitor, one plate is kept at higher potential, and charge accumulates on it; due to induction, equal and opposite charges are induced on the other plate, which is kept at lower potential. Capacitors are used to maintain a constant flow of electricity through a circuit.

• Xerography

Xerography is the dry photocopying method based on the principle of electrostatics. Its components consist of a lamp, aluminum cylinder, selenium, toner, corona wire, and heated roller. 

When light from the lamp falls on the paper to be photographed, the paper reflects the light towards the aluminum cylinder. Since the aluminum cylinder is covered with a selenium sheet, a photoconductor, it absorbs the light and acts as a conductor. Then the positive charge is added over the cylinder by corona wire, then a charged image of the document is formed on the cylinder. Now the toner with electrons from the selenium sheet sticks to the positively charged image on the drum. Then a page with a positive charge is passed through the cylinder, the heated roller then melts the toner, and the ink sticks to the paper.

• Tandem Accelerator

Tandem Accelerator is used to increase the kinetic energy of positively charged particles like protons. In the Tandem Accelerator, negative ions are produced at higher potential. In the Van de Graaff generator, positive ions are produced at a higher potential.

In the second stage of the Tandem Accelerator, electrons are stripped off, and negative charges are converted to positive charges. And then, positive charges are accelerated to ground potential.

Conclusion

• By bringing a charged body near an uncharged object, an equal and opposite charge is induced on the near-surface of the uncharged object. This phenomenon is called Electrostatic Induction.
• During Electrostatic Induction, the net charge remains zero on the object, meaning it remains electrically neutral. Since there is no transfer of charge from one body to another, the charges are just redistributing themselves due to the influence of nearby charges.
• Some applications of Electrostatic Induction are- 

1. Van de Graaff generator
2. Tandem Accelerator
3. Capacitors
4. Xerography
5. Inkjet printers

• Selenium sheet used in Xerography is a photoconductor. When light falls on it, it acts as a conductor, but it acts as an insulator in the dark.