Magnetism and Electricity

Transcription

1 Magnetism and Electricity UNIT 7 Student Reader E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

2 Front Cover: The front cover shows a photograph of a girl with her hair standing straight up. This is a result of static charge that has built up in her hair after she slid down the slide. E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

3 Unit 7: Magnetism and Electricity Table of Contents Section 1: Electric Charges 4 Studying Lightning What is Lightning? Opposites Attract Static Electricity Attracting Objects Static Charge and Lightning What is an Electroscope? Static Charge Investigation Section 1 Review Section 2: Magnetic Forces 14 The World s Strongest Magnet Magnets Have Magnetic Fields Magnetic Fields Investigation 1 Magnetic Fields Investigation 2 Engineering Investigation Section 2 Review Science Words to Know 29 E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

4 1 Electric Charges Studying Lightning Joseph Dwyer studies lightning. He uses cameras and other tools to learn more about it. Joseph has even been in a plane that went through a thunderstorm. The pilot didn t mean to go through the thunderstorm. It was dangerous. But Joseph collected data from inside the storm. This is Joseph Dwyer. Joseph and other scientists still have a lot of questions about lightning. How does it get started? How does it move? Why does it strike one object and not another? E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

5 What is Lightning? Scientists know some facts about lightning. Lightning flashes happen because of atoms. Atoms are the tiny parts that make up all matter. The air is made up of atoms. Water is made up of atoms. Grass and trees are made up of atoms. lightning in a field Every atom has smaller parts. It has protons. Protons have a positive charge (+). They stay in the nucleus. The nucleus is in the center of the atom. Every atom also has electrons (-). Electrons have a negative charge. Electrons orbit the nucleus. This is a model of an atom. E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

6 Opposites Attract The positive charge of the protons attracts the negative charge of the electrons. To attract means to pull together. Opposite charges attract each other. This is a pulling force. Like charges repel. To repel means to push apart. Two negative charges push away from each other. Two positive charges also push away from each other. This is a pushing force. Like charges repel. Opposite charges attract. Sometimes the negative charges in an object separate from the positive charges. This causes objects to have either a positive electric charge or a negative electric charge. The buildup of electric charge in an object is static charge. E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

7 Static Electricity Static charge can happen when two materials rub against each other. In some materials, electrons move from one material to the other. The material with more electrons now has a negative charge. The material with fewer electrons now has a positive charge. Look at the picture on the right. The child rubbed against the slide going down it. Electrons moved from the child to the slide. A static charge built up. The slide has more electrons. This gives it a negative charge. The child now has fewer electrons. She has a positive charge. Each of the child s hairs has the same positive charge. Chris Darling Static charge makes this girl s hair stand up. These positive charges repel each other. Each piece of hair pushes away from every other piece of hair. The hairs try to get as far from each other as possible. This makes the child s hair stick straight up. Something similar happens when you take off a hat. Electrons move from your hair to the hat. Your hair is positively charged. This is why it sticks up. E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

8 Surfaces that build up static charge are usually insulators. Electrical insulators don t allow electrons to pass through easily. This is how the electrons can build up in the object. Glass, rubber, plastic, and ceramic are good insulators. Electrical conductors are materials that electrons can easily pass through. Metals are common conductors. Silver, copper, bronze, and aluminum are all metals. They are good electrical conductors. These plugs have metal prongs. Metal is a conductor. They are covered in plastic. Plastic is an insulator. These wires are metal. Metal is a conductor. They are covered in plastic. Plastic is an insulator. E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

9 Attracting Objects Objects with an electric charge can attract other objects without touching them. For example, a balloon is an insulator. If you rub it against your clothes, electrons move from your clothes to the balloon. The balloon has more electrons, so it has a negative charge. If you hold the balloon near a wall, an attractive force pulls the balloon and the wall together. If you have two negatively charged balloons, a repellent force pushes the balloons apart. The more charge an object has, the stronger force it will exert on other objects. E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

10 Static Charge and Lightning Lightning happens when clouds get a static charge. Electrons move to the bottom of the cloud. They have a negative charge. The tops of the storm clouds now have fewer electrons. This gives them a positive charge. Objects on Earth s surface below a storm cloud become positively charged. The positive charge on Earth's surface attracts the electrons. The positive charge of other storm clouds can also attract the electrons. Electrons move from the storm cloud to the ground or to other storm clouds. We see this movement of electrons as a flash of lightning. Lightning flashes are moving electrons. Protect yourself from lightning. Go inside during a storm. Stay away from tall trees, the beach, or metal structures. They all attract lightning. E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

11 What is an Electroscope? Scientists can study electric charge with an electroscope. An electroscope is a scientific instrument. It is used to see if an object has an electric charge. Electroscopes are made up of a conducting material. This is so that electrons can move through it easily. If an object that has an electric charge is placed near the electroscope, electrons move freely through the conducting material. The electroscope includes one or more parts that can move. These parts often hang down. When electrons move through the electroscope, the parts will move because they become negatively charged. E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

12 Name: Date: Static Charge Investigation Focus question: Look at the list of materials in Table 1 below. Will materials with a high static charge cause the foil sheets in your electroscope to move farther apart compared to materials with a low static charge? Use your electroscope and the test materials to explore the question. Procedure 1. Rub the plastic PVC rod on the cloth for 10 seconds. 2. Bring the charged rod near the paper clip on your electroscope. 3. Measure the distance between the foil sheets on the electroscope with a ruler. Record the measurement in Table Discharge the paper clip by touching it with your fingers. The foil sheets should return to their original position. 5. Repeat Steps 1-4 with the plastic cup, wooden dowel, and glass plate. Table 1: Comparing Static Charge of Different Materials when Rubbed with Cloth Materials Relative Static Charge When Rubbed with Cloth Distance Between Foil Sheets (mm) Plastic (PVC) rod high plastic (cup) wood (dowel) glass (plate) high medium-low low E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

13 Section 1 Review Reading Comprehension Questions: 1. How does an object become negatively charged? 2. What happens to the electrons in the clouds when we see a flash of lightning? 3. Why does an object that has a positive charge move toward an object that has a negative charge? 4. What happens when two negatively charged objects are close to each other? 5. What is the main idea of this section? What details support this main idea? E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

14 2 Magnetic Forces The World s Strongest Magnet The world s strongest magnet is in Florida. It took 10 years to build this magnet. It is 6.7 meters (22 feet) tall. This is part of the world s strongest magnet. Florida State University Scientists from around the world come to Florida for the magnet. They carry out experiments that use the magnet. Most scientists stay for a week. Andreas Neubauer is a scientist from Germany. He stayed for six months. Engineers have designed new types of materials with the help of the magnet. This is possible because matter acts differently inside a powerful magnetic field. E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

15 Magnets Have Magnet Fields A magnet is any object that produces a magnetic field. A magnetic field is the area around a magnet that attracts or repels other magnets or magnetic materials such as iron. A magnetic field applies a force to other magnets or magnetic materials within it. This force can be a push or a pull. This horseshoe magnet attracted the iron bar. The force of this attraction pulled the bar to the magnet. All magnets have a north pole and a south pole. The north pole of one magnet always attracts the south pole of another. This is a pulling force. However, two north poles will always repel each other. Two south poles will also repel each other. These are pushing forces. E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

16 Magnets are useful. They can attract or repel magnets or magnetic materials without touching them. But objects are only affected by a magnet within in its magnetic field. A magnet s magnetic field is invisible. It moves from the magnet s north pole to its south pole. Stronger magnets have a larger magnetic field. A magnet s strength depends on its material. There are different kinds of magnets depending on their properties. Permanent magnets stay magnetized without electricity. Refrigerator magnets are permanent magnets. Temporary magnets act like a permanent magnet when they are within a strong magnetic field. They lose their magnetism when the magnetic field goes away. Paperclips and iron nails are temporary magnets. Many objects that have iron are magnetic. They can be permanent magnets or temporary magnets. It depends on how they are made. E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

17 Name: Date: Magnetic Fields Investigation 1 Focus Question 1: What does the magnetic field of a bar magnet look like? Investigate the question using iron filings to observe the shape of the magnetic field around one bar magnet. Diagram 1. Observe the shape and size of the patterns the iron filings make around the small bar magnet on the poster paper. Draw a diagram of what you see in the space below, using the magnet outline as a guide. N S E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

18 Focus Question 2: How do the magnetic fields of attracting magnets compare to the magnetic fields of repelling magnets? Use iron filings to observe the shape of the magnetic fields around different sets of magnets to investigate the question. Diagrams 1. Draw the patterns the iron filings make around the attracting magnets in the space below. Use the magnet outlines as a guide. N S N S 2. Draw the patterns the iron filings make around the repelling magnets in the space below. Use the magnet outlines as a guide. N S S N E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

19 Name: Date: Magnetic Fields Investigation 2 Focus Question: Does the size of a ceramic magnet affect how far away it can attract paper clips? Test ceramic magnets of different sizes to investigate the question. Materials 1 small bar magnet 1 medium bar magnet 1 large bar magnet 1 ruler 1 small paper clip Procedure 1. Lay the ruler on a flat surface. Place the small magnet at 0 centimeters. The magnet should stand up on its short edge. Place the small paper clip at 10 centimeters. 2. Move the magnet 0.5 centimeters closer to the small paper clip. Observe how the small paper clip responds to the magnet. 3. Repeat Step 2 until the magnet pulls the paper clip over to it. Record the distance the magnet was from the paper clip when it attracted the paper clip. 4. Repeat Steps 1-3 two more times, first with the medium magnet and then with the large magnet. How far away was the magnet from the paper clip when the magnet pulled it over? (cm) Table 1: Comparing Magnetic Fields of Ceramic Magnets of Different Sizes Ceramic Magnet Size Small Medium Large E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

20 Name: Date: Engineering Problem desired features of the solution solution limits Criteria 1. The device must use magnets. 2. In a single test, the device must lift and move as many metal clips as possible from Station 1 to Station 2 in 10 seconds or less. 3. The workers can t touch the metal clips or magnets with their hands. Constraints 1. The available materials are limited. E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

21 Research 1. What is a magnet? 2. How could magnets be useful in the device for the factory? E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

22 Survey Available Materials Complete the materials survey chart below. Draw a simple sketch of each material. Record a description of what each material is made from. List 1-2 properties of each material. (Examples include physical properties such as thickness, flexibility, shape, relative weight, or any other physical characteristics that you notice.) Materials Survey Chart Name Quantity Sketch Made From small craft sticks 10 Properties small paper clips large craft sticks 5 5 cups 3 bar magnet (3 cm x 1 cm) bar magnet (2 cm x 1.5 cm) 2 2 E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

23 clothespins 2 cylinder 1 dowel 1 paint stirrer 1 felt 1 sheet string 1 meter bar magnet (7.5 cm x 1 cm) bar magnet (4 cm x 2 cm) round magnet E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

24 Possible Solutions Use what you know about the problem and your research to list two possible solutions to the problem, given the available materials and what you know about magnets Diagram and Build Prototype Draw a diagram of your chosen prototype in the space on the next page. Label each material used in your prototype. Title the diagram. E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

25 Test Procedure 1. Set up the Factory Test Template with 15 large paper clips. 2. Use your prototype device to pick up large paper clips in the area marked Station 1 on the test template. 3. Move the paper clips over to the area marked Station 2 on the template. 4. Release the paper clips from your device onto the Station 2 area. Record how long it took to pick and place the paper clips. 5. Return the paper clips to Station 1 and repeat Steps 1-4 with Prototype 2 and Prototype 3. Data Record your test data in Table 1 on the next page. E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

26 Table 1: Comparing Prototype Pick-and-Place Devices Time to pick up and How many paper clips place paper clips did it pick up and (seconds) move? Prototype 1 Prototype 2 Prototype 3 Refine or Replicate Use your test data to explain which prototype solution best solved the problem (and why) and if you would refine or replicate any of your designs based on your data. Our data show that Prototype # best solved A&B Factory s problem of moving metal clips from one station to another in less time because E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

27 Based on our data, we recommend engineers should Prototype # (refine or replicate) for A&B Factory to solve their problem. E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

28 Section 2 Review Reading Comprehension Questions: 1. What makes a magnet attract another magnet? 2. What makes a magnet repel another magnet? 3. How far away can a magnet act on another magnet? 4. What is the main idea of Section 2? What details support this main idea? 5. What is the connection between Section 1 and Section 2? E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

29 attract to pull together Science Words to Know electric conductor a material that electrons can easily pass through electric insulator a material that electrons cannot pass through easily magnet an object that produces a magnetic field; has a north and south pole; attracts or repels other magnets or magnetic materials such as iron magnetic field the area around a magnet that attracts or repels other magnets and magnetic materials such as iron permanent magnet an object that stays magnetized without electricity repel to push apart static charge the buildup of electric charge in an object temporary magnet an object that acts like a permanent magnet when it is within a strong magnetic field E3 Student Reader v. 9 Unit 7 Page KnowAtom TM

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