Grade Nine Science

SNC 1D

Static Electricity Note

Review of Atomic Structure:

The Typical Atom

Nelson Physics 11 / The nucleus is the small region in the middle of the atom that contains protons and neutrons.
Neutrons have almost the same mass as protons but carry no electric charge.
Electrons move around the nucleus and have 1/2000 the mass of a proton.
Usually the atoms of everyday matter have the same number of electrons as protons. Atoms are electrically neutral.
When atoms gain electrons they are electrically negative. The atom has become a negative ion since it has more electrons than protons.
When atoms lose electrons they are electrically positive. The atom has become a positive ion since it has more protons than electrons.
Protons are fixed in the nucleus and are not lost or gained by atoms unless a nuclear reaction occurs.

Charge and Macroscopic Objects

The atoms of an electrically neutral object can gain electrons and become a negatively charged object or lose electrons and become a positively charged object. The build up of stationary charges (electrostatic charge) on an object is called static electricity. An object which has an excess of electrons has a negative charge, an object which has a deficiency of electrons has a positive charge. Materials that make up objects fall into two main categories conductors and insulators.

CONDUCTORS / INSULATORS

Example: A plastic comb pulled through your hair will gain electrons from your hair and gain a negative charge. The hair has lost electrons and gained a positive charge. Notice protons have nothing to do with the charging of objects.

Interaction of Charges

The interaction of charged particles/objects can be studied using the Laws of Electric Charge.

Laws of Electric Charge
Like charges repel each other.
Unlike charges attract each other.
Charged objects can attract neutral objects.

Charging Objects

Objects can be given an electric charge in three main ways; charging by friction, charging by contact and charging by induction.

Charging by friction

Two objects made of different materials are rubbed together, an example is rubbing a glass rod with silk. One of the materials (silk) has a stronger attraction for electrons than the other material (glass). The material with the stronger electron attraction (silk) gains electrons and becomes negatively charged, the other material (glass) loses electrons and becomes positively charged.

The strength of a material's attraction for electrons has been studied and quantified. It is summarized in a table called the electrostatic series (Table 1).

Chapter 9 Nelson