Activity 3
Aim: To charge an object by induction
Materials required: An uncharged metal sphere, an insulated
stand, an ebonite rod and a woollen cloth
Procedure:
negatively
charged rod
metal
sphere
A
B
insulated
stand
a.
B
B
XX
XX
STEP 1. Mount the sphere on the insulated stand.
STEP 2. Rub the ebonite rod with woollen cloth to make it
negatively charged.
TEP 3. Bring the negatively charged rod close to the sphere
(side A) without touching (Fig. 8.5a). The negatively
charged rod repels the electrons at side A. The electrons
on side A move to side B. Hence, side A gets positively
b.
charged, whereas side B gets negatively charged
Fig. 8.5 Charging an
(Fig. 8.5b).
object by induction
w, if we touch side B with a finger, the negative charges that have collected there will flow
ough our body to Earth, and the metal sphere will be left with a net positive charge (Fig. 8.50).
Answers
Answer:
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Explanation:
Charging a Two-Sphere System Using a Negatively Charged Object
One common demonstration performed in a physics classroom involves the induction charging of two metal spheres. 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 (see diagram i. below) so as 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 and vice versa. If a rubber balloon 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. This is 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. Subsequently, there is a mass migration of electrons from sphere A to sphere B. This electron migration causes the two-sphere system to be polarized (see diagram ii. below). 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. 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 (see diagram iii. below). Meanwhile, 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 (see diagram iv. below). 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. (This distribution of positive charge on a conductor was discussed in detail earlier in Lesson 1.)