Download Electric Field Hockey

Kreutter/Costello/Albano: Electric Fields 1
Did You Know?
Electric Field Lines 1
Electric Field Lines An Electric field can be represented with Electric field lines. They have the
following properties.
 The ___________________of the Electric field line shows the ____________________ of the Electric field at
that point.
 Electric field lines are ____________________ 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
Electric field, the lines themselves are __________________________.
 Electric field lines start on ____________________ charged objects (arrows point __________)and end
on ____________________ charged objects (arrows point ______). 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 _________________ of the lines near that point represents the ___________________ of the field at
that point. More lines ___________________together mean the Electric field is ___________________ at
that point. The ___________________ the Electric field lines are to each other, the ___________________
the Electric field is. If there are ___________________ lines___________________apart the Electric field is
___________________.
 An Electric field whose lines are parallel to each other is called ___________________ electric field. The
field is the same strength at every point.
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/Costello/Albano: Electric Fields 1
1.2 Reason.
.
a) Can E field lines ever cross?
Draw the electric field lines for:
a) A positively charged particle
b) A negatively charged particle
c) 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/Costello/Albano: 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/Costello/Albano: 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/Costello/Albano: 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?
Kreutter/Costello/Albano: Electric Fields 1
1.5 Reason
Faraday Cage- A Faraday cage or Faraday shield is an enclosure formed by conducting material or mesh.
Such an enclosure blocks external static and non-static electric fields by channeling electricity through the mesh,
providing constant voltage on all sides of the enclosure. Since the difference in voltage is the measure of
electrical potential and cancels out, no current flows through the space.
Faraday cages are named after the English scientist Michael Faraday, who invented them in 1836.
http://www.topgear.com/uk/videos/car-lightning
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.