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Glow Bulb: How Can a Fluorescent Tube Glow Without Being Connected to an Electric Current?

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Author: Janice VanCleave

Problem

How can a fluorescent tube glow without being connected to an electric current?

Materials

• dishwashing liquid
• paper towels
• fluorescent tube (size and shape of the tube does not matter and it can be a burned-out tube)
• large bath towel (longer than the fluorescent tube)
• plastic report folder

Procedure

NOTE: This experiment is best performed at night or in a darkened room without windows.

CAUTION: Care should be taken not to press too hard, as the tube could break.

1. Ask an adult to wash and thoroughly dry the outside of the fluorescent tube with paper towels.
2. Stretch out the bath towel near the edge of a table.
3. Lay the fluorescent tube on the bath towel.
4. Darken the room by turning off the lights.

Results

The fluorescent tube starts to glow and the light moves back and forth with the movement of the plastic.

Why?

Rubbing the tube results in a build-up of charges, called static charge, on the outside of the glass. This outside charge attracts charged particles inside the tube. The phosphor powder coating on the inside of the tube gives off light when struck by these charged particles.

Let's Explore

1. Can other materials produce a static charge on the glass? Repeat the experiment, replacing the plastic report folder with materials such as a piece of plastic food wrap, a wool scarf, and an inflated balloon. Science Fair Hint: Record your results in a data chart similar to the one shown here. Describe the light's intensity as bright, medium, or dim.
2. Will other types of light bulbs give the same results? Repeat the original experiment, replacing the fluorescent tube with an ordinary filament light bulb.

Show Time!

1. People have not always been able to light up their home by simply flipping a switch. Find out about the history of lamps and lighting. Construct a display chart similar to the one shown here to indicate various steps in the advancement of lighting.
2. The light intensity of all light bulbs is not the same. A simple photometer (an instrument used to measure the brightness of a light) can be constructed by sandwiching a piece of aluminum foil between two 5-inch × 2 1/2-inch × 1/2-inch (12.7-cm × 6.4-cm × l.3-cm) blocks of paraffin (paraffin can be found where food canning supplies are sold). The dimensions of the blocks are not critical, as long as the blocks are of equal size. Use rubber bands to hold the blocks together. Lay a yardstick (meterstick) on the edge of a table. Take two lamps without shades and place one at each end of the stick. Insert different wattage bulbs in the lamps. Hold the photometer so that the edge points toward you and the flat sides face the lamps. Move the photometer above the measuring stick between the bulbs until the edges of both sides of the photometer look equally bright. At this point, an equal amount of light is entering each side and being reflected by the foil. The photometer will be closer to the bulb with the lesser intensity (lower wattage).

Check it Out!

1. A fluorescent tube shines brightly and steadily when connected to a constant flow of electricity. Look up lighting in different encyclopedias to discover how fluorescent lights work.
2. Thomas Alva Edison produced the first practical incandescent light bulb in 1879. There were many failures before the successful bulb was produced. Find out more about the history of the first electric lights. What role did a whisker from Mr. Edison's assistant and sewing thread from Mrs. Edison's sewing basket play in the development of bulbs that could burn for more than a few hours?