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

2. 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?

3. 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

4. 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

5. 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

6. 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

7. 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

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

9. 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

10. 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

11. 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

12. 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

13. 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

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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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.

24. 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.