# Static Electricity

#### Students’ Learning Outcomes

·
 Explain the production of static electrical charges in some common materials. ·         Explain the phenomenon of lightening.

#### Information for Teachers

·         All materials are made of atoms which contain protons, electrons and neutrons.
·         Protons have positive charges, electrons have negative charges and neutrons have no charge.
·         The protons and electrons are equal in numbers in an atom. Therefore net charge on an atom is zero.
·         The electrons are loosely attached to the atom.
·         When two objects are rubbed together, some electrons from one object move onto the other.
·         Thus, the number of electrons on one object becomes greater than the number of protons in it, so negative charge appears on it.
·         The number of electrons left on the other object becomes less than the number of protons on it, so positive charge appears on it.
·         There is attraction between two oppositely charged objects.
·         There is repulsion between two similarly charged objects.
·         When oppositely charged clouds come close to each other, they collide with each other due to great attraction and thus a big spark is produced. It is called as lightning.

#### Material / Resources

Balloons, thread, stand, woolen cloth, plastic comb, metallic key, textbook

#### Worm up Activity

·         Ask the students; have they ever observed that when a plastic comb is rubbed through hair and brought near small paper bits, it begins attracting these paper bits.
(Expected response: Yes)
·          Ask: have they observed that a woolen trouser often sticks to the hair on their legs?
(Expected response: Yes)
·         Now tell the students that when a plastic comb is rubbed through hair, it becomes charged and this starts attracting hair and paper bits. Similarly, the trouser on rubbing with body hair also becomes charged and starts attracting body(hair) and sticks to legs. Tell the students that many such objects acquire charge when rubbed with each other.  For example:
—When glass rod is rubbed with silk cloth, it becomes charged.
—When an ebonite rod is rubbed with woolen cloth, it also gets charged.

#### Activity 1

·         Divide the class into suitable groups.
·         Ask a student from each group to suspend an inflated balloon with the stand by means of a thread.
·         Direct him to bring a piece of woolen cloth near it. Ask: Does it attract the balloon towards it?
(Expected response: No)
·         Ask the student to rub the balloon vigorously with a woolen cloth and then remove it away.
·         Direct him to bring the cloth close to the balloon slowly. Ask the student: Does the cloth attract the balloon this time?
(Expected response: Yes)
·         Ask the students: Why does the cloth attract balloon after rubbing?
(Expected response:  because the cloth and balloon have acquired opposite charges)
·         Ask the students to suspend two inflated balloons with the stands with the help of thread and place them at some distance from each other.
·         Ask them to bring the balloons closer by moving the stands.
·         Ask them: Do the balloons attract or repel each other or nothing happens?
(Expected response: Nothing happen)
·         Ask them to rub each balloon with woolen cloth and bring them closer again and observe their movements.
·         Ask them: Do they attract or repel each other?
(Expected response: They attract each other because they have opposite charges.)
·         After these activities explain the cause of attraction or repulsion of balloons.
·         Tell them that when certain objects are rubbed with each other, they become charged.
·         When two objects are rubbed some electrons from one object move onto the other. In this way the number of electrons on one object becomes greater than protons in it and thus it becomes negatively charged. On the other hand, the number of electrons on the other object becomes less than protons in it and thus it becomes positively charged.

#### Activity2

(This activity should be performed in a dark room)
·         Give each group a plastic comb, a woolen cloth, an iron nail or key.
·         Ask the students to charge the comb by rubbing it with the woolen cloth.
·         Ask them to touch the charged comb gently with a metallic key and observe.
·         Ask the students: What do they see?

(Expected response: A spark)
·         Explain that when charged comb is brought closer to the key, opposite charge appears on the near part of the key. Spark is produced when oppositely charged objects touch each other.
·         Explain that similarly when oppositely charged clouds come closer to each other, they collide due to great attraction between them and thus a big spark is produced. It is called lightning.

#### Sum up/ Conclusion

·         The charge is the basic property of matter.
·         The charges are of two types. One type is called positive and the other negative.
·         On rubbing two objects, positive charge appears on one object and negative charge on the other object.
·         Opposite charges attract each other and similar charges repel each other
·         Spark is produced when two oppositely charged objects touch each other.

#### Assessment

·         To assess the understanding of the students ask the following questions:
—–How can an inflated balloon be charged?
—–why do positive or negative charges appear on the objects on rubbing?
—–How does lightning occur?