eActivities
Christmas Light Circuits
Christmas lights can be strung and arranged to produce dazzling front-yard scenery. They can also be used for education. Obtain an unused string of Christmas lights and cut out a set of five lights. Strip the wire at both ends of the set. Use alligator clips to momentarily attach the ends to a 9-volt battery. Next, remove a bulb and see if you get the same results when the lights are connected back to the battery. Can you build a circuit where one light can be removed while the other lights stay lit?
(Hint: you will have to cut the set into five individual lights.)
Use this simple setup to explore the basic series and parallel circuits. Challenge yourself: build a more complex circuit by using the lights in combinations of series and parallel; use miniature solar panels; or add a few motors.
Antifreeze
What do automotive antifreeze and ice cream have in common? Here is a related question that at first glance may seem rather simple and not related: At what temperature does water freeze? If you are an astute observer of the weather you might immediately respond 32˚F. But if you think about it, not all water is the same. I think Adam Sandler’s Bobby Boucher put it best when he said, "Now that’s what I call high quality H2O!"
Sure, all water is made up of two atoms of hydrogen and one atom of oxygen, but sometimes the water (solvent) contains dissolved substances (solute). When a solute is added to a solvent, the freezing point of the solvent is reduced. This is known as a colligative property – a property that is dependent on the concentration of a solute in a solvent, and not on the identity of the solute. In the case of freezing point reduction, the amount of reduction is dependent on the concentration of solute.
MATERIALS:
• 10 oz glass bottle of carbonated water
• Ice
• Salt (NaCl)
• Thermometer
• A one- or two- Liter container
INSTRUCTIONS:
Peel the label off of the seltzer water bottle to more easily see what’s happening inside. Place a small amount of ice on the bottom of the container, then stand the bottle up in the ice. Sprinkle a small amount of salt on the ice, followed by a 2-3 cm layer of ice. Repeat alternating layers of ice and salt until the bottle is covered up to the neck. Insert the thermometer into the ice next to the bottle approximately 8-9 cm deep. Cool the bottle to a temperature of -8°C to -10°C. This will take approximately 30 minutes. The seltzer water should still be fluid; if it is chilled to greater than -10°C it will freeze. Remove the bottle from the ice/salt solution and wipe it clean with a towel. Notice that the bottle is still in liquid form. What will happen when you crack the seal on the bottle cap? The fluid in the bottle should immediately begin to freeze or turn solid. The bottle will be completely frozen (a slushy consistency) in 10-20 seconds. Why?
In this activity the water is the solvent and carbon dioxide is the solute. In the sealed bottle the concentration of carbon dioxide gas is great enough to reduce the freezing point of the water to approximately -10°C. The CO2 solute disrupts the ability of the water molecules to organize into the solid ice. However, when the CO2 is released from the solution the concentration of solute is immediately reduced, quickly raising the freezing point of the solvent.
A tasty application of the freezing point depression is the making of homemade ice cream. The ice cream mix is put into a metal container that is surrounded by crushed ice. The addition of the salt depresses the freezing point of the water/ice that has several degrees below its normal freezing point. The heat transfer out of the ice cream mix allows it to freeze. It is the same method you used to cool the seltzer bottle.
Ethylene glycol and other forms of antifreeze are added to an engine’s cooling water, keeping the water in its liquid state at temperatures below its normal freezing point.
The use of freezing-point depression has also evolved in some animals that live in very cold environments. Some species of arctic-living fish survive in freezing temperatures by increasing the concentrations of physiologically inert substances into their tissues, and thus decreasing their freezing point.
Mountain Maker: Can you form a mountain?
Earth’s surface is made of moving slabs of rock called plates. Sometimes these plates crash into each other. How could such a collision create mountains? Find out with this FUN activity.
Materials:
• Scissors
• Plastic wrap
• Tape
• Ruler
• 2 cardboard rectangles - 9 centimeters (3.5 inches) long and 6 cm (2.5 inches) wide
• 4 ounces modeling clay
Steps:
1. Cover the top of a table with plastic wrap. You will need to tape the plastic down.
2. Cut another piece of plastic wrap that’s 15 cm (6 in.) long and 6 cm (2.5 in.) wide.
3. Place the sheet of plastic you just cut over one cardboard rectangle. Line up one short end of the plastic wrap with one short end of the cardboard.
4. Tape these two short ends together. The plastic should cover the top of the cardboard and dangle over one edge.
5. Repeat Steps 2 to 4 with the remaining cardboard rectangle.
6. Divide the modeling clay into two equal parts. Shape each part into a rectangle that’s 15 cm (6 in.) long and 6 cm (2.5 in.) wide.
7. Press each clay rectangle onto the plastic wrap covering each cardboard rectangle. Some of the clay will extend beyond the cardboard but will still be stuck to the plastic wrap.
8. Place the clay-covered rectangles on opposite ends of the desk. The dangling pieces of clay should face each other.
9. The clay and plastic wrap represent the rock of Earth’s plates. Slowly push the two slabs of “rock” together. What happens when the plates touch?
10. Keep pushing the plates toward each other. What happens to the slabs of rock?
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