Topic 3.2 - How Do Electrical Charges Behave?

Topic 3.2 - How Do Electrical Charges Behave?

Key Points

• Electrons carry a negative charge, and protons carry a positive charge.

• Opposite charges attract each other, and like charges repel each other.

Concept 1: Electrons carry a negative charge, and protons carry a positive charge

Negative charges

• The charges of electrons

• Surround the nucleus; can be rubbed off a material

Positice charges

• The charges of protons

• Part of the nucleus of atoms and are held firmly in place

Negative Charges and Positive Charges

• Charging by friction: Charging a material by rubbing

• When electrons are rubbed off a material, it becomes positively charged

• Material gains electrons and becomes negatively charged

Electrically Neutral and Electrically Charged Materials

• Uncharged Materials:

• Before two materials are rubbed together: they have equal numbers of positively charged protons and negatively charged electrons

• Materials are electrically neutral (equal numbers of positive and negative charges cancel each other out)

Charged Materials

• If electrons rubbed off one material, the protons stay behind and the material becomes positively charged

• The material that gains the electrons becomes negatively charged

• Electrically charged materials have an unequal number of positive and negative charges

Electrostatic Series

• Different materials have different tendencies to either gain electrons or lose electrons.

• If rabbit fur is rubbed with cat fur the rabbit fur will ______ electrons while the cat fur will ______ electrons. Therefore

• Rabbit Fur will be _______

• Cat Fur will be _________

Electrostatic Series

• If human hair is rubbed with a rubber balloon the human hair will ______ electrons while the balloon will ______ electrons. Therefore

• Human Hair will be _______

• Balloon will be _________

Concept 2: Opposite charges attract each other, and like charges repel each other.

The Law of Electric Charge

• Opposite charges attract each other

• Like charges repel each other

The law of electric charge applies to all individual charges

• Every negative charge attracts every positive charge

• Every negative charge repels every other negative charge

• Every positive charge repels every other positive charge

Attraction Between Charged Objects and Neutral Objects

• The law of electric charge explains why charged objects attract neutral objects

• All neutral objects have an equal number of protons and electrons

Attraction Between Charged Objects and Neutral Objects (continued)

• Why a charged balloon sticks to an electrically neutral wall

• When a charged object (balloon) is brought near a neutral object (wall), the electrons in the neutral object do not come off

• Negative charges in the wall are pushed away from the surface by the negative charges on the balloon

• Positive ends of the molecules in the wall are attracted to the negative charges on the balloon

• This attraction is strong enough to hold the balloon to the wall