Download Electric Field Hockey

Kreutter: Electric Fields 1
Observe the bottle: Draw a picture of the bottle. What explanation can you come up with for the
behavior of the stuff in the bottle? Another good question—what is the stuff in the bottle?
Did You Know?
Electric Field Lines An E field can be represented with E field lines. They have the following properties.
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The direction of the E field line shows the direction of the E field at that point.
E field lines are representations only; they help us visualize the effects charged objects will have on
other objects within the space that surrounds them. While we can feel effects of an E field, the lines
themselves are imaginary.
E field lines start on positively charged objects and end on negatively charged objects. The arrows
point in the direction a positive charge would go (the direction of the force a positive charge would
experience if it were located at that point).
The density of the lines near that point represents the strength of the field at that point. More lines
closer together mean the E field is stronger at that point.
An electric field whose lines are parallel to each other is called uniform electric field.
1.1. Diagram Jeopardy. E field vectors due to one or more electrically charged objects are shown below.
Indicate with circles, including the + or – signs, the charged source objects creating the field.
a.
b.
Kreutter: Electric Fields 1
1.2 Reason.
.
a) Can E field lines ever cross?
b) What is the direction of the E field directly between two positive equal charged particles? Explain why this
happens. Draw an example.
c) What is the direction of the E field directly between two negative equal charged particles? Explain why this
happens. Draw an example.
Kreutter: Electric Fields 1
Electric field Hockey
On the computers, go to http://phet.colorado.edu/en/simulation/electric-hockey. Answer the questions that
follow. The simulation is also available on the portal under
Academic>HSN>ClassProjects>Handouts>Kreutter.Physics>electrichockey_en
a) Set the difficulty to “practice”. When you drag a positive charge out of the bin on the top right and put
it on the hockey table, which direction is there an arrow pointing from our black test charge? Why does
it point in this direction?
b) Drag a Negative charge out of the bin and place it on the field. You will notice the arrow that comes
from the test charge points towards this new charge placed on the table. How does the arrow’s length
depend on the distance between the source charge and the test charge?
c) Position the source charges so you can shoot the test charge into the goal. Press start and try it out.
d) With a single positive and negative charge on the table separated by about an inch, click the box that
says “Field.” Describe the direction the clear/white arrows on the table point. What do you think these
“Field” arrows represent?
e) Using a few combinations of charges, try to score goals on all three of the difficulty settings. (Don’t let
the puck leave the table)
Kreutter: Electric Fields 1
1.3 Draw E field lines for the electric field created by the source charged objects described in the table that
follows.
A) A positively charged object
B) A point-like positively
charged object with twice the
magnitude of charge as in part
A.
C) A point like negatively
charged object
D) A point-like negatively
charged object with twice the
magnitude of charge as in part
C.
E) Two positively charged
point objects of equal
magnitude charge, separated
by a distance “d”
F) Two negatively charged
point objects of equal
magnitude charge, separated
by a distance “d”
G) A small negatively charged
object and a small positively
charged object of equal
magnitude charge separated by
a distance “d”
H) A small positively charged
object and a small negatively
charged object with twice the
magnitude of charge separated
by a distance “d”
Kreutter: Electric Fields 1
1.4 Represent and Reason
a) Circle the correct sign of the charge for the particles represented in A through I.
b) Examine the charges G, H, & I. Which of the charged objects has a bigger magnitude?
c) What would happen to the E field lines if you kept adding identical charged objects to the left of G and
to the right of I? Draw out a diagram of the E -field lines if 6 charged objects are added to the ends of G
and I.
1.5 Represent and reason. Imagine that a small, positively charged object moving toward the top of the page
enters an electric field with the lines shown below.
a) Sketch on the illustration an approximate path the
object follows as it moves through the field. The
initial direction of the object as it enters the field is
sketched on the picture.
b) Do those lines represent the path the object will
follow? What do they represent?
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Kreutter: Electric Fields 1
1.6 Reason A hollow metal box is placed in a uniform electric field. Negatively charged electrons in the metal
can move freely.
a) Indicate the electric charge distribution in the metal
due to the external electric field.
b) Draw electric field lines caused by this induced
charge distribution on the surface of the box and
discuss the magnitude of the total E field inside the
box. Compare the density of these lines with the lines
of the external electric field.
c) Discuss how your reasoning for parts (a) and (b) helps explain why it is safe to sit in a car during a lightning
storm.