Charge Transfer by Induction, Charge Transfer by Induction Using a Negatively Charged Object (For CBSE, ICSE, IAS, NET, NRA 2022)

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Charge Transfer by Induction

Definition

  • Induced-charge separation is a shift in the position of electrons in a neutral object that occurs when a charged object is brought near it whereas charging by induction is the charging of a neutral object by bringing another charged object close to; but not touching, the neutral object.
  • Charging more than one object by induction a positively charged object can be used to induce a charge in a neutral object.
  • One can also use two objects at the same time to permanently charge the objects.
  • In sphere A, the electrons are attracted by the positive charge on the balloon.
  • The electrons the balloon draw electrons in sphere A to the left side. The right side of the sphere becomes negatively charged.
  • Electrons in sphere B are attracted to sphere A and are transferred. Keep the balloon in place and remove sphere B from sphere A, makes sphere B permanently charged positively.
  • Electrons are unable to move back. Remove the balloon form sphere A allows the electrons to spread throughout the sphere, yet it is still negatively charged.

Charge Transfer by Induction Using a Negatively Charged Object

  • The metal spheres are supported by insulating stands so that any charge acquired by the spheres cannot travel to the ground.
  • The spheres are placed side by side to form a two-sphere system. Being made of metal (a conductor) , electrons are free to move between the spheres - from sphere A to sphere B

Charging by Induction

Charging by Induction
  • If a balloon of rubber material is charged negatively (perhaps by rubbing it with animal fur) and brought near the spheres, electrons within the two-sphere system will be induced to move away from the balloon.
  • Simply the principle that like charges repel.
  • Being charged negatively, the electrons are repelled by the negatively charged balloon and being present in a conductor, they are free to move about the surface of the conductor.
  • There is a mass migration of electrons from sphere A to sphere B. This electron migration causes the two-sphere system to be polarized
  • Overall, the two-sphere system is electrically neutral. Yet the movement of electrons out of sphere A and into sphere B separates the negative charge from the positive charge.
  • So, looking at the spheres individually, it would be accurate to say that sphere A has an overall positive charge and sphere B has an overall negative charge.
  • Once the two-sphere system is polarized, sphere B is physically separated from sphere A using the insulating stand. Having been pulled further from the balloon, the negative charge likely redistributes itself uniformly about sphere B.
  • Also, the excess positive charge on sphere A remains located near the negatively charged balloon, consistent with the principle that opposite charges attract.
  • As the balloon is pulled away, there is a uniform distribution of charge about the surface of both spheres.
  • This distribution occurs as the remaining electrons in sphere A move across the surface of the sphere until the excess positive charge is uniformly distributed.

Charge Transfer by Induction Using a Positively Charged Object

Consider the Graphic below in Which a Positively Charged Balloon is Brought Near Sphere A

Charging by Induction

Charging by Induction
  • The presence of the positive charge induces a mass migration of electrons from sphere B towards (and into) sphere A.
  • So, this movement is induced by this simple principle that opposites attract. Negatively charged electrons throughout the two-sphere system are attracted to the positively charged balloon.
  • This movement of electrons from spheres B to sphere A leaves sphere B with an overall positive charge and sphere A with an overall negative charge. The two-sphere system has been polarized.
  • With the positively charged balloon still held nearby, sphere B is physically separated from sphere A.
  • The excess positive charge is equally distributed across the surface of sphere B.
  • The excess negative charge on sphere A remains towards the left side of the sphere, positioning itself close to the balloon.
  • Once the balloon is removed, electrons again distribute themselves about sphere A until the excess negative charge is evenly distributed across the surface.
  • Finally, sphere A becomes charged negatively and sphere B becomes charged positively.

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