- University of Virginia
- Physics Department
A Physical Science Activity
2003 Virginia SOLs
- show and understand that like charges repel each other and opposite charges
- apply information about static electricity to identify missing charges in
static electricity problems.
Demonstration of an Electroscope
- The teacher should have a basic electroscope that is assembled
and ready when the students come in.
- Apply glue to a small strip of aluminum foil and wrap a single
layer around a straw.
- Cut the foiled straw into one centimeter long pieces and place
a piece of thread (about 15 cm long) between the straw and the
foil before the glue dries. You now have a pith-ball! (The thread
can also be added later).
- Tape the straw onto an inverted styrofoam cup with the
flexible end of the straw facing up. Bend the straw so that the
short end is horizontal and about 7 cm above the cup.
- Cut several slits into the straw and hang a pith-ball by
slipping the string into the slit of the straw. You now have an
Questions to ask students:
- What do you think will happen when I rub another Styrofoam cup
with the fur and bring it near the pith-ball?
- What do you think will happen when I touch the cup to
the pith ball?
You may want to hang several pith-balls from the straw and repeat
- What do you think will happen if I touch one pith ball and not
Click here for background
information on static electricity.
To print out the Student Copy only,
- 2 identical balloons per group of students
- Fur or Wool cloth for each group
- Water sprayer per 2 groups
- Blow-up the balloons and tie thread to the ends of each
- Tie the balloons together.
- Have the students hold the uncharged balloons by the thread
and move balloons together. Record their observation and make a
sketch. (Figure A).
- Rub each balloon with the wool. Move one balloon near the
other but do not allow them to touch. (Balloons will not touch
like Figure B). Hold by thread.
- While the balloons are repelling each other, have the students gently mist
the balloons with water. Record their observations and make a sketch. (They
will fall back against together like Figure A).
To print out the Data Sheet only,
- Why did the balloons repel each other after they were
rubbed with the fur/wool?
- Why did the balloons fall back towards each other
after they were sprayed with water?
- Are there other ways besides water that we could use
to have the balloons come back together?
- During which time of the year would it be best to do
experiments using static electricity?
- What effect does damp weather have on electrical
Answers to Worksheet
Explanation: After rubbing the balloons with the fur/wool, the
balloons have the same charge and will repel each other. Using water
droplets on the balloons carries the charge away from the balloons
which leaves them neutral. As the balloons become neutral, they will
fall back together but will not be attracted to each other. Another
way to neutralize the balloons is to touch them with a moist or damp
hand. One needs to remember that only where the balloons are wet is
where the charges are carried away. The part of the balloon that is
not wet will still attract to the other balloon where it is not wet.
Let the students work in groups and have the students make a new
design on paper or actually build an electroscope. They can use
different charged objects to get their electroscopes to work. If they
are designing on paper or building one, I would have them write down
the purpose of the different parts (bottle, stopper, wire, foil, and
charged object). If building, let the students try out different
things to see what works and what doesn't.
Students with Special Needs
Adapt as needed for children who have physical disabilities. These children
may need help blowing up the balloons, tying the thread to the balloon, and
rubbing the balloon with the fur or wool. I would ask your resource teacher
for additional help if you need it.
Click here for further
information on laboratories with students with special needs.
Data sheet to be completed during the laboratory.