An electroscope is used to detect the presence of electric charges, to determine whether these charges are positive or negative, and to measure and indicate their intensity. By the help of this electroscope we will see the movement of electrons.
Things Required:
Aluminium foil, as thin as possible
Glass jar, 1 qt. (1 litre)
Soft plastic lid to cover the top of jar
Large paper clip
Needle-nosed pliers
Modelling clay
Balloon, 9 inches (23 cm)
Pencil
Scissors
Adult helper
Directions:
Cut two strips of aluminium foil ½ inches × 2 in. (1 cm × 5 cm). Use the point of the pencil to make a small hole in the top of each foil strip. Ask an adult to use the pliers to reshape the paper clip into a loop at the top and two hooks on the bottom (see the diagram). Use the pencil to make a hole in the centre of the plastic lid. Push the loop of the wire through the hole in the plastic lid and mould a small piece of clay around the base of the loop to hold it in place. Hang the foil strips on the hooks of the wire. Place the lid on top of the jar.
Inflate the balloon and rub it on your hair. Your hair must be clean, dry and oil-free. Hold the balloon near the loop, on top of the jar.
This Is What Happens:
The metal leaves move apart when the charged balloon is held near the metal loop.
Science Behind It:
The instrument made is called an electroscope, or charge detector. The metal strips move when the loop is placed in an electrically charged area. Electrons are rubbed off your hair and onto the balloon, charging the surface of the balloon with a negative charge. Holding the negatively charged balloon near the metal loop causes the negative electrons on the surface of the metal to move away from the balloon because like charges repel, that is, move away from each other. Electrons move down the metal wire and build up on the aluminium strips. Since like charges repel each other, the two negatively charged strips move apart.
