Question

A student rubs a ball against a glass tabletop. The ball becomes negatively charged because
1. electrons left the ball
2. protons left the  ball.
3. electrons flowed from the tabletop to the ball due to friction.
4. electrons flowed from the tabletop to the ball because of contact.

Answer 1

Correct Answer - Option 3 : electrons flowed from the tabletop to the ball due to friction.

The correct answer is option 3) i.e. electrons flowed from the tabletop to the ball due to friction.

CONCEPT:

​Object acquire charge by three methods:

• ​Charging by friction: When two objects are rubbed, due to friction there occurs a charge transfer. 
  • An object loses its electrons, while the other object gains electrons.
  • The object that loses electrons becomes positively charged and the object that gains electrons becomes negatively charged.
• Charging by conduction: In this method, a charged conductor is brought in contact with another neutral body.
  • The neutral body acquires a charge such that the measure of charge on the neutral and charged conductor is the same.
• Charging by induction: This method is used to charge an object without actually touching the charged object.
  • The charged object is brought near the uncharged object. The end of the uncharged object near the charged object develops a charge of the opposite polarity. 

EXPLANATION:

• When the ball is rubbed against the tabletop, due to friction loss of electrons takes place from the tabletop.
• As a result, the ball becomes negatively charged.
• Therefore, the ball becomes negatively charged because electrons flowed from the tabletop to the ball due to friction.