Chapter 20 Electricity Lightning provides a powerful display of electrical energy.

20.1 Key Concepts What produces a net electric charge? What determines whether an electric force is attractive or repulsive? What determines the strength of an electric field? What are three ways in which charge is transferred? How does a static discharge occur?

When you take clothes out of a dryer, some of them can ____________ together. If you pull the clothes apart in a darkened room, you can see ___________ that are like tiny bolts of lightning Lightning and “static cling” have similar causes – the movement of _________________ stick sparks electric charges

Electrons have _________ charges and protons have ____________ charges Electric Charge Recall that electric charge is a property that causes subatomic particles to ____________ or _____________ one another. Electrons have _________ charges and protons have ____________ charges attract repel negative positive

How many protons does this atom have? And electrons? Electric Charge How many protons does this atom have? And electrons? This atom is ___________ because it has an ________ number of positive and negative charges 8 8 neutral equal

An excess or shortage of electrons produces a _______ electric charge. If an atom gains electrons (e-), it becomes a ______________ charged ion. If an atom loses electrons (e-), it becomes a ______________ charged ion. An excess or shortage of electrons produces a _______ electric charge. negatively positively net

The SI unit of electric charge is the __________ (C). It takes about __________________ electrons to produce a single coulomb. A lightning bolt is about ____________ coulombs of charge, and a camera flash is about _______ coulombs. coulomb 6.24 x 1018 10 to 20 0.025

Electric Forces Recall that like charges ____________, and opposite charges _____________. The force of attraction or repulsion between electrically charged objects is _____________ ___________. repel attract electric force

Doubling the net charge on one object ____________ the electric force. Electric Forces Doubling the net charge on one object ____________ the electric force. Electric force and net charge have a _____________ proportional relationship doubles directly

Electric Forces Doubling the ____________ between the objects _______________ the electric force to one fourth the original force. Electric force and distance have an _____________ proportional relationship distance reduces inversely

Electric forces also cause _______________ and other contact forces Inside an atom, electric forces are much ________________ than gravitational forces. form chemical bonds Electric forces also cause _______________ and other contact forces stronger friction

Electric Fields The effect an electric charge has on other charges in the space around it is the charge’s electric _________________. . field Field of a positive charge Field of a negative charge

The strength of an electric field depends on… Electric Fields The strength of an electric field depends on… the ______________ of charge that produces the field and on the ______________ from the charge. amount distance

Static Electricity and Charging Static electricity is the study of the _________________ of electric charges. behavior Charge can be transferred by… __________________ friction contact induction

Static Electricity and Charging When studying charge transfers, keep in mind the law of conservation of charge… states that the total charge in an isolated system is _______________. when there is a charge transfer, the total charge is the ____________ before and after the transfer occurs. constant same

Rubbing a balloon on your hair causes charging by friction. Electrons move from your ____________ to the _________________ because atoms in rubber have a greater attraction for electrons than atoms in hair. The balloon picks up a net _____________ charge. Your hair loses electrons and becomes ________________ charged. hair balloon negative positively

Static Electricity and Charging Charging by Contact A ________________ generator builds a charge on a metal sphere. Touching the sphere transfers charge by contact. The sphere is still charged, but its net charge is ____________________ Van de Graaff reduced

Charging by Induction Walking on a carpet builds a ________________ charge on your body. The negative charge in your hand repels electrons in a metal doorknob Describe the movement of the electrons in the doorknob as the hand approaches. negative They move away from the hand

Charging by Induction The doorknob is still _____________, but charge has moved ______________ it. This is induction, a transfer of charge _____________ contact between materials. neutral within without

Why do you get a shock from a doorknob? Static Discharge Static discharge occurs when a _____________ through which charges can move forms ________________. pathway quickly Why do you get a shock from a doorknob? __________ becomes charged when the gap between your finger and the doorknob is _________. This air provides a path for _______________ to flow. Air small If the room is dark, you can even see the spark. electrons

Lightning is a more ______________ discharge. Charge can build up in a storm cloud from _________________ between moving air masses. Negative charge in the lower part of the cloud induces a positive charge in the _____________ below. Eventually the ________ between becomes charged, forming a _________________ for electrons to travel from the cloud to the ground. dramatic friction ground air pathway

Assessment Questions Which of the following would double the electric force between two charged objects? doubling the mass of the objects cutting the net charge of both objects in half doubling the net charge of one of the objects cutting the distance between the objects in half

Assessment Questions The attractive or repulsive effect an electric charge has on other charges in the space around it is the charge’s electric force. electric field. static electricity. static discharge.

An object becomes charged by induction when there is a Assessment Questions An object becomes charged by induction when there is a transfer of electrons, as the object rubs against another object. transfer of charge, as it contacts another charged object. transfer of charge by motion of electrons within the object. a sudden movement of electric charge from another object.