Download Thursday - cloudfront.net

Electricity and Magnetism: Electric Fields
Physics 5e: Students know charged particles are sources of electric fields and are subject to
the forces of the electric fields from other charges
Focus Question: Why does your hair stand up when you rub it with a balloon?
Charged Particles: A Brief Review
Electricity is created by the movement of charged particles. Everything is made of
_____________ which are composed of charged particles.
List the two fundamental (subatomic) particles that have charge and what charge they have:
1. Particle:
Charge:
2. Particle:
Charge:
Like charges repel (push each other away) so ______________ repel ______________ and
________________ repel _____________.
Opposite charges attract, so _________________ is attracted to _________________. This is
called __________________________. It holds ___________ bonds together!
This __________________ attraction is a fundamental principle. It is a part of the
electromagnetic force, which is one of only four fundamental forces in our universe.
We learned that these charged particles can be transferred between atoms. Which of the
particles is almost always transferred? Why?
Once an electron is transferred, the atom is an ___________ because it is no longer
_______________. That means it has a __________________.
____________________ ions will be attracted to ___________________ ions because
OPPOSITES ATTRACT!
We can extend our description of transferring electrons to the macroscopic (big enough to see)
level by saying that electrons may be transferred between two materials. When they are
transferred, the material that loses electrons will become _____________________ and the
material that gains electrons will become ______________________.
Experimentation: Discover Electric Fields!
Physics 5e, Investigation and Experimentation 1d
Perform the following experiments with your group and answer the questions after each
experiment. You will follow the steps of the scientific method; some of the steps are given to
you. When you have finished all experiments, you should answer the final conclusion
questions.
Materials:
3 balloons with X’s drawn on one side of the balloon
A piece of paper with confetti on it
A piece of paper with pepper on it
1 soda can
1 plastic bag
General Observations about the materials:
Experiment 1:
Question: Can you make your hair stand up using only the balloon?
Hypothesis/Predict:
Test Predictions:
Methods (describe what you did):
Results (describe what happened):
Conclusions:
Did your results agree with your hypothesis?
Why do you think your hair was able to stand up after rubbing it with the balloon?
Hint: think about electrostatic attraction!
Experiment 2:
Question: Can you make two balloons repel each other?
Hypothesis/Prediction:
Test Predictions:
Methods:
1. Get two balloons.
2. Rub the two marked sides of the balloons on your hair
3. Hold the balloons close togetherwith the x-ed sides facing each
other and observe what happens
Results:
Conclusions:
Did your results agree with your hypothesis?
Why do you think the balloons acted the way they did?
Experiment 3:
Question: Can you make two balloons attract?
Hypothesis/Prediction:
Test Predictions:
Methods:
1. Get two balloons.
2. Rub one balloon on your hair, rub the other with the plastic bag.
Be sure to rub the marked side of both.
3. Hold the balloons next to each other and observe what happens
Results:
Conclusions:
Did your results agree with your hypothesis?
Why do you think the balloons acted the way they did?
Experiment 4:
Question: Can you make the confetti / pepper move without touching them? Hint: begin
by rubbing the balloon on your hair.
Hypothesis/Prediction:
Test Predictions:
Methods (describe exactly what you did):
Results:
Conclusions:
Did your results agree with your hypothesis?
Did you have to touch the confetti to make it move? If not, what did you have to
do?
Experiment 5:
Question: Can you make the soda can roll from one end of the table to the other without
touching it?
Hypothesis/Prediction:
Test Predictions:
Methods (describe exactly what you did):
Results:
Conclusions:
Did your results agree with your hypothesis?
Did you have to touch the soda can?
Final Questions:
What do you think is happening when you rub the balloon with your hair or with the
paper bags?
Why would the balloons in experiment 3 repel each other, yet stick to your hair in
experiment 1 and make it stand up?
Were you able to move the objects without touching them? Did it matter how close you
put the balloon to the can? What does this tell you about electrostatic attraction?
Electric Fields: Formation and Forces
All matter is made of _________________. Atoms are made of __________, _____________,
and ____________________. Protons have a ______________ charge and Electrons have a
__________________ charge.
In experiments 1-3, ____________________ were transferred from one material to another.
This created two charged objects. The object that lost electrons became ________________
because it had more ________________ than electrons. The object that gained those
electrons became ______________ because it had more ___________________ than
_____________________.
**Key Point: These charged objects and any charged particle (proton or electron) produce
an ______________________________.
Comprehension Check: What produces an electric field?
An electric field is just a region of space in which a force is exerted on another charged particle.
This force causes movement of that charged particle; if you put a charged particle within the
field, it will move in some direction. This force is a result of the charged particles that caused
the electric field. For example:
If a collection of negatively charged particles create an electric field and we put a
positive particle within the field, the positive particle will be pulled closer to the negative
particles because opposites ___________________. The negative particles are
creating a field. That field is causing the movement of the positive particle (force).
If an electron is put in this same field, the electron will be pushed away because like
charges _______________.
Thought question: Do the particles that we put in this electric field cause a field
themselves and exert a force on the negative particles that are making the field?
Think of the balloon. When you rub a balloon on your hair, you are transferring electrons
from your hair to the balloon. The balloon is now _________________. When you rub a
balloon with a plastic bag, the balloon gives electrons to the bag. The balloon is now
____________________.
What happens when you put the two hair balloons together? Why?
What happens when you put a hair balloon near the bag balloon? Why?
**Key Point: An electric field exerts ________________ on any charged particle. It causes
that charged particle to move.
Electric fields can also act on objects that have a neutral charge because they contain
_________________ and _______________ in their atoms. When a charged object is placed
near a neutral object, the charged particles in the neutral object re-arrange because opposites
_______________ and like charges ___________. This is called ______________________
_________________. Draw it here:
Comprehension Check: Why was either balloon able to pick up the pepper and move the soda
can if those objects are both neutral?
Force of an Electric Field
Comprehension Check: Where in class today have you seen evidence to prove that electric
fields exert force?
Electric fields may act on a particle or object over a __________________ (they may exert force
on something even if they are not touching), but the force gets ___________________ as you
move the particle farther from the field. Therefore, the distance between two charged particles
and the force between them are an _____________ relationship. As distance increases, force
decreases. This is because of the following equation, where F = force and R = distance
between to the two charges.
F = kq1q2 / r2
*as distance between to charges increases, the force of the electric field decreases
Think: How did you make the soda can roll? Did you have to touch it with the balloon?
**Key Point: The force of an electric field can act over a distance, but it gets less strong
as you move further away.
Comprehension Check: What evidence do you have that electric fields exert force across a
distance?
Practice: Charged Particles and Electric Fields
Complete the charts:
Definition
Characteristics
Definition
Characteristics
Electric
Field
Charged
Particle
Examples
Examples
Non-examples
Non-examples
Rewrite the three key points here:
1.
2.
3.
Fill in the blanks: _______________________ create an _______________________, which
exerts _____________________ and causes other charged particles ___________________.
Answer the questions:
What is an electric field?
How is an electric field created?
What happens when you transfer electrons from one material to the next?
What happens when charged particles enter an electric field?
If you have a positive charge that creates an electric field, what will happen when you
put a negative particle within the field? What will happen when you put a positive
particle within the field?
If two charged particles are moving away from each other, is the force of the electric field
between them increasing or decreasing? Why?
Focus question: Why does your hair stand on end when you rub it with a balloon? Be
sure to use the words electrons, electric field, and force in your answer. Be detailed!
Answer the questions:
1. Two particles have opposite charges. As they move away from each other, what happens
to the force that each particle exerts on the other?
a. It becomes larger
b. It approaches zero
c. It approaches infinity
d. The two charges repel instantly so no force is exerted
Why?
2. Freddy rubbed a metal ball with cloth and found that the metal ball became positively
charged. What best explains how this happened?
a. Protons were transferred into the metal ball
b. Electrons were transferred into the metal ball
c. Protons were transferred into the cloth
d. Electrons were transferred into the cloth
Why?
3. Maria charges a balloon by rubbing it on her hair. She then moves the negative balloon
close to a metal sphere, but does not touch the sphere. What will happen in the metal
sphere?
a. The charges will redistribute so that positive charges are closest to the balloon
b. The charges will redistribute so that negative charges are closest to the balloon
c. Electrons will transfer into the balloon from the metal sphere
d. Protons will transfer into the balloon from the metal sphere
Why?
4. What causes an electric field?
a. Gravity
b. Force
c. Movement
d. Any arrangement of charged particles
Why?