Expt 012 -- Electrifying Patterns

The gas in a round flask glows from the electric energy of a Tesla coil. Glowing rays of light discharge across the flask. You can move the glowing rays by moving your hand around the flask.

Chemical Concepts

1. One form of energy may be changed to another form of energy. For example, electrical energy may be changed to heat or light energy.
2. If atoms or molecules are close together, electrical energy is frequently changed to thermal energy. Molecules bump one another and vibrate.
3. If atoms or molecules are farther apart as in a gas at low pressure, the electrons in atoms or molecules may be excited by the electrical energy. The electrons emit light when the electrons move back to their normal state.
4. Charged areas are attracted to a grounded object--in this case, you.

Safety

• Be certain that the Tesla Coil is grounded and that your hands are dry.
• Tape the flask with clear tape. Implosions are possible. (The tape was omitted from the movies to afford a clearer view of the inner parts.)

Procedure

This demonstration requires a strong vacuum pump. If you do not have one, see BBExperiment 011.

1. Assemble the apparatus as described below in Lab Hints. Observe electrical safety rules.

   !!!Click here to See Movie. Click |> or <| to step the slides forward or back.

2. Darken the room. The experiment is most impressive in a completely dark room. Turn on the Tesla Coil. Pull a vacuum with the pump. Observe. It takes a minute or two for the pressure to drop enough. Move your hand over the outside of the flask. The charge conducts through you to ground.

   !!!Click here to See Movie (closeup).

   !!!Click here to See Movie.

   If you have a problem, secure tubing connections and try again. The problems are usually leaks at the connections.

Optional: Pick up a fluorescent light bulb (not attached to a fixture). Observe. Have a student touch the other end of the bulb.

Questions

1. How do fluorescent lights work?
2. Which elements or ions might be emitting light in the flask?

Handout Makeup

Name ___________________________ Class _______

Teacher __________________________

BeckerDemos 012 Electrifying Patterns

Watch the movies.

1. Describe the demonstration.
2. Answer the questions.

Curriculum-

This experiment fits in when discussing different forms of energy or when discussing atomic structure. The demonstration may lead to discussing electronic energy levels in atoms and molecules.

Activity-

Demonstration - Teacher Only

This works well as a teacher demonstration followed by discussion of energy transformations or electronic energy levels.

Safety-

• Be certain that the Tesla Coil is grounded and your hands are dry.
• Tape the flask with clear tape. Implosions are possible. Tape was omitted from the movies so that you could see the inner parts more clearly.
• Use plenty of glycerin when inserting the tubing in the rubber stopper.

Time-

Construction of apparatus: 15-20 minutes

Class Time: 5-20 minutes The variable time is for discussion of the experiment.

Materials-

• a vacuum pump
• 1 1-liter or 2-liter round bottom flask with 2-holed stopper to fit
• a very stable ring stand and clamp to hold flask in an inverted position
• 1 20-30 cm piece of insulated stiff wire (a coat hanger wrapped in electrician's tape works)
• 1 10-cm piece of glass tube
• rubber vacuum hose to connect the glass tube to your vacuum pump. See Lab Hints.

Optional:

• a fluorescent light bulb

Lab Hints-

• Cut the wire about 6 cm longer than the distance from the stopper to the center of the flask. Each end must be long enough to coil.
• Strip 2 cm of insulation from one end of the wire. Make a coil to support the wire in one hole of the 2 hole stopper. Select a nail, screw, or piece of tubing a little smaller then the hole in the rubber stopper. Use the pliers make 2 turns around it. Push the tip of the Tesla coil into one hole of the rubber stopper from the outside of the stopper. From the inside of the stopper, screw the coil into the hole in the stopper until the wire touches the Tesla coil. A diagram is shown below.

  

• The Tesla coil tip must fit snugly inside the hole of the stopper to prevent air leaks at the same time it is touching the wire. If there is a problem, remove the wire and coil it to a different size. The wire should be supported straight up from the stopper.
• Strip 4 cm of insulation from the other end of the wire. Compact a large exposed surface area by bending the wire into a loop. Insert a piece of glass tubing into the other hole of the stopper. Use a snug-fitting rubber vacuum hose to connect the glass tubing to the vacuum pump.
• Insert the stopper securely into the flask. The wire should extend straight into the flask, with the looped end positioned more or less in the center of the flask bulb (like the filament in a light bulb). The Tesla coil and the tubing to the vacuum pump should extend out the other side of the stopper. Clamp the flask upside down near the top of the ring stand.
• CAUTION: The set-up is likely to be somewhat top-heavy. Use a larger ring stand if necessary.
• Test the apparatus. If you have a problem check the connections. A bit of heavy grease like stopcock grease may help, but tight connections are most important.
• !!!Click here to See Movie. Repeat from above. Click |> or <| to step the slides forward or back.

Answers-

Q1. How do fluorescent lights work?

A1. A small amount of gas in the tube is excited by an electric arc. The gas glows at distinct energies (colors) as the electrons in the atoms decay to the stable state. Subsequent excitation of a solid state phosphor coating on the inside of the lamp results in a glow with a continuum of wavelengths. (The gas in the lights is mercury. Mercury lines are evident when measured with a spectroscope.)

Q2. Which elements or molecules might be emitting light in the tube in this experiment?

A2. Air is left behind. Argon, nitrogen, and oxygen are the most abundant. Students have no way to distinguish which substance is glowing.

Key Words 1-

electrical energy, energy, light energy, energy level