Energy Transfer in a Flash-Light. (Teacher Copy)

Transcription

1 Energy Transfer in a Flash-Light (Teacher Copy) Florida Sunshine State Standards Benchmark: SC.B AA The student identifies forms of energy and explains that they can be measured and compared. (Also assess SC.B and SC.B ) Objectives: SC.B AA I can identify different forms of energy and discuss how energy can be transformed from one from to another. Background Knowledge: Energy is the ability to do work. Work is done when a force causes an object to move in the direction of the applied force. Kinetic energy is energy of motion and depends on mass and speed. All objects have kinetic energy. Potential energy is stored energy or the energy an object has due to its position. There are several forms of energy, i.e.: mechanical, chemical, electrical, electromagnetic (including visible light), nuclear, thermal (heat), light, and sound. All forms of energy can be measured and compared. An energy conversion is a change from one form of energy to another. An example of an energy conversion would be when you turn on a fan; electrical energy from the power plant to the electrical outlet causes the blade on the fan to turn. This is an example of electrical energy converting to mechanical energy. Due to friction, some energy is always converted into thermal energy during an energy conversion. As a result, energy conversions are never 100% efficient. Energy is conserved within a closed system because energy cannot be created or destroyed; it can only be changed from one form to another. The loss of useful energy from a system to its surroundings causes the amount of disorder to increase. Electricity is a flow of energy by the movement of electrons. If an electrical appliance is to work properly, there must be a supply of electrons and they must be able o flow through a complete circuit. When the circuit is broken, the electrons are stopped and the appliance does not work. There are several components of a circuit that can be easily demonstrated using a simple flashlight. The circuit must have an energy source, such as a power outlet or batteries. The battery is stored potential energy. When the circuit is complete; it will release chemical energy as kinetic energy. A wire or metal conductor must connect the positive source of the battery to a light bulb which

2 connects back to the negative source of the battery. This creates an electric circuit path along which negative charges can flow. There are several transformations that occur during this simple experiment. Chemical energy is converted into electrical energy when the circuit is complete. To complete the circuit a switch can be turned on, this is an example of mechanical energy. Some of the electrical energy is then converted to light energy when the bulb lights up. Light energy is converted to thermal (heat) energy, when the bulb feels warm. If using a wire conductor you may feel the wire get warm. As electrical energy is carried through the wire, some of it is converted into thermal energy as resistance. Materials: (per group) Mini tree lights and wires Cardboard toilet paper tube or paper towel tube Two rubber bands (¼ in. width) 6 cm x 10 cm aluminum foil strip Masking tape Two C or D batteries Scissors Assorted objects to be used as a switch Engage: At the beginning of the class, turn off the lights in the classroom, light a match and let it burn for a few minutes and then turn on a flashlight. Ask the students to compare and contrast the role of energy in both objects. Explore: Procedures: 1. Tape the batteries together with the negative end of one battery to the positive end of the other battery. Wrap one of the rubber bands around the batteries (end to end) so that they are firmly held together, maintaining contact between the two opposite-charged ends. 2. Fold an aluminum foil strip in half lengthwise, so that you have a strip 3cm x 10cm. Fold the strip in half lengthwise one more time so that it is 1.5cm wide. Finally, reinforce the strip with a 9cm piece of masking tape placed along one side of the strip. 3. At the negative end of the batteries, slip the piece of foil under the rubber band so that it makes contact with this end of the battery. 4. Tape the light bulb with connecting wires to the positive end of the batteries. 5. Cut the cardboard tube lengthwise and wrap securely the two batteries inside. Tape the cardboard wrap with masking tape to create a tight hold for the batteries.

3 6. Leave the foil strip outside of the tube. Create a switch from an object that is a conductor. Attached the switch to the cardboard tube and foil. 7. Slip the stripped end of one of the light bulb wires under the rubber band so that it contacts the positive end of the batteries. 8. The foil strip that is attached to the negative end of the batteries should be long enough to reach the stripped end of the other light bulb wire. If using an object for a switch make sure it is connected to the end of the foil and is able to make contact with the wire. 9. Touch the end of the wire to the foil or switch and watch your flashlight glow. Explain: 1. Draw the flashlight in the box below. At each point in the sketch list the energy transformations that took place in the circuit. Label at least five energy transformations. 2. Explain the energy transfer: The energy stored in the batteries changed to energy as the electrons were flowing through the circuit. The batteries have energy which is transformed into energy in the wires and then into energy. 3. Turning the switch on and off was an example of 4. Some energy increased the temperature of the flashlight, becoming Draw and label the energy transformations that took place in the flashlight. Elaborate: Reading First Through Science - Have students read I Knew an Old Woman: Energy Conversions, pp Complete the follow up questions.

4 Evaluate: 1. When a light is turned on, electrical energy is converted to light and heat energy. Which of the following best describes the balance of energy in this system? A. The sum of the heat and light energy produced is greater than the electric energy flowing into the bulb. B. The electric energy flowing into the bulb is greater than the sum of C. The heat energy produced is greater than the electric energy that flows into the bulb. D. The electric energy that flows into the bulb is equal to the sum of ANS. D 2. In active solar heating systems, water absorbs heat from the sun. This heat is then transferred to air that is pumped through a building. Some of the heat absorbed by the water is not transferred to the air and is lost. Why is the heat lost? A. Heat is destroyed. B. Heat is transferred to light energy. C. The energy transfer is not 100% efficient. D. Water evaporates and can t transfer energy. ANS. C

5 Energy Transfer in a Flash Light (Student Copy) Objectives: SC.B AA I can identify different forms of energy and discuss how energy can be transformed from one from to another. Background Knowledge: Energy is the ability to do work. Work is done when a force causes an object to move in the direction of the applied force. Kinetic energy is energy of motion and depends on mass and speed. All objects have kinetic energy. Potential energy is stored energy or the energy an object has due to its position. There are several forms of energy, i.e.: mechanical, chemical, electrical, electromagnetic (including visible light), nuclear, thermal (heat), light, and sound. All forms of energy can be measured and compared. An energy conversion is a change from one form of energy to another. An example of an energy conversion would be when you turn on a fan; electrical energy from the power plant to the electrical outlet causes the blade on the fan to turn. This is an example of electrical energy converting to mechanical energy. Due to friction, some energy is always converted into thermal energy during an energy conversion. As a result, energy conversions are never 100% efficient. Energy is conserved within a closed system because energy cannot be created or destroyed; it can only be changed from one form to another. The loss of useful energy from a system to its surroundings causes the amount of disorder to increase. Electricity is a flow of energy by the movement of electrons. If an electrical appliance is to work properly, there must be a supply of electrons and they must be able o flow through a complete circuit. When the circuit is broken, the electrons are stopped and the appliance does not work. Materials: (per group) Mini tree lights and wires Cardboard toilet paper tube or paper towel tube Two rubber bands (¼ in. width) 6 cm x 10 cm aluminum foil strip Masking tape Two C or D batteries Scissors Assorted objects to be used as a switch

6 Explore: Procedures: 1. Tape the batteries together with the negative end of one battery to the positive end of the other battery. Wrap one of the rubber bands around the batteries (end to end) so that they are firmly held together, maintaining contact between the two opposite-charged ends. 2. Fold an aluminum foil strip in half lengthwise, so that you have a strip 3cm x 10cm. Fold the strip in half lengthwise one more time so that it is 1.5cm wide. Finally, reinforce the strip with a 9cm piece of masking tape placed along one side of the strip. 3. At the negative end of the batteries, slip the piece of foil under the rubber band so that it makes contact with this end of the battery. 4. Tape the light bulb with connecting wires to the positive end of the batteries. 5. Cut the cardboard tube lengthwise and wrap securely the two batteries inside. Tape the cardboard wrap with masking tape to create a tight hold for the batteries. 6. Leave the foil strip outside of the tube. Create a switch from an object that is a conductor. Attached the switch to the cardboard tube and foil. 7. Slip the stripped end of one of the light bulb wires under the rubber band so that it contacts the positive end of the batteries. 8. The foil strip that is attached to the negative end of the batteries should be long enough to reach the stripped end of the other light bulb wire. If using an object for a switch make sure it is connected to the end of the foil and is able to make contact with the wire. 9. Touch the end of the wire to the foil or switch and watch your flashlight glow. Explain: 1. Draw the flashlight in the box below. At each point in the sketch list the energy transformations that took place in the circuit. Label at least five energy transformations. 2. Explain the energy transfer: The energy stored in the batteries changed to energy as the electrons were flowing through the circuit. The batteries have energy which is transformed into energy in the wires and then into energy. 3. Turning the switch on and off was an example of 4. Some energy increased the temperature of the flashlight, becoming

7 Draw and label the energy transformations that took place in the flashlight. Elaborate: Reading First Through Science - Have students read I Knew an Old Woman: Energy Conversions, pp Complete the follow up questions. Evaluate: 3. When a light is turned on, electrical energy is converted to light and heat energy. Which of the following best describes the balance of energy in this system? E. The sum of the heat and light energy produced is greater than the electric energy flowing into the bulb. F. The electric energy flowing into the bulb is greater than the sum of G. The heat energy produced is greater than the electric energy that flows into the bulb. H. The electric energy that flows into the bulb is equal to the sum of ANS. D 4. In active solar heating systems, water absorbs heat from the sun. This heat is then transferred to air that is pumped through a building. Some of the heat absorbed by the water is not transferred to the air and is lost. Why is the heat lost? E. Heat is destroyed. F. Heat is transferred to light energy. G. The energy transfer is not 100% efficient. H. Water evaporates and can t transfer energy. ANS. C