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Republic of the Philippines
Department of Education
ACTIVITY SHEETS IN GENERAL PHYSICS 2
GRADE 12
QUARTER 3, WEEK 6 AND 7
ELECTROMAGNETISM
MELC:
Differentiate electric interactions from magnetic interactions (STEM_GP12EM- IIIh-54) Evaluate the total magnetic flux through an open surface (STEM_GP12EM-IIIh-55) Describe the motion of a charged particle in a magnetic field in terms of its speed, acceleration, cyclotron radius, cyclotron frequency, and kinetic energy (STEM_GP12EM-IIIh-58) Evaluate the magnetic force on an arbitrary wire segment placed in a uniform magnetic field (STEM_GP12EM-IIIh-59) Evaluate the magnetic field vector at a given point in space due to a moving point charge, an infinitesimal current element, or a straight current-carrying conductor (STEM_GP12EM-IIIh-60) Calculate the magnetic field due to one or more straight wire conductors using the superposition principle (STEM_GP12EM-IIIi-62) Calculate the force per unit length on a current carrying wire due to the magnetic field produced by other current-carrying wires (STEM_GP12EM-IIIi-63) Evaluate the magnetic field vector at any point along the axis of a circular current loop (STEM_GP12EM-IIIi-64) Solve problems involving magnetic fields, forces due to magnetic fields and the motion of charges and current-carrying wires in contexts such as, but not limited to, determining the strength of (STEM_GP12EM-IIIi-66)
Prepared by:
MICHELLE A. AGULAY
Master Teacher I
BACKGROUND INFORMATION
ELECTROMAGNETISM
Everybody is familiar with a toy magnet, that mysterious little U-shaped device that picks up needles or pins and holds them indefinitely in what seems to be like magic. As a child you probably played with small magnets. But magnet is far from being a mere toy. It is an essential part of machines, tools and some measuring devices. You have heard of a magnetic compass that helps navigators keep their course at sea. When you hold a phone receiver to your ear, a magnet records the vibrations set up by the voice of the person talking at the other end. Electric motors also contain magnets to function. Particle accelerators like cyclotron contain thousands of magnets as well.
Electricity and magnetism cannot be separated. Magnetism plays an important role in the study of electricity. Whenever electric current appears, there is magnetism. The operation of many electrical devices such as radios, TV sets, motors and other devices depends on the magnetic effects of electric current.
This activity presents the discovery of magnetism and some of the fundamental experiments and laws showing the relationship between electricity and magnetism. In reading this activity, you should pay attention to the nature of the force exerted on moving charges by a magnetic field. In addition, you need to understand the way in which an electric current produces a magnetic field. You will also learn how two important current carrying shapes of wire: a long straight wire and a circular loop or solenoid produce magnetic field.
Discovery of Magnetism
Have you ever used a compass to find a direction? If you have, you are doing something that was first done by the Chinese in the twelfth century. Historians believe that the Chinese were the first to build compasses to help them navigate. They made use of a property of certain materials that had been discovered centuries before – magnetism. To know more about the discovery of magnetism, read the history of magnetism.
A. Magnetic Substances
A substance that possesses magnetic properties is a magnet. It attracts iron and faces the same direction when moving freely. All materials have the property of being attracted or repelled. Substances like iron and steel are strongly attracted to magnets. These substances are called ferromagnetic. Nickel and cobalt are also ferromagnetic. These materials are often called magnetic materials. Some substances, such as wood, aluminum, platinum and oxygen, are just slightly attracted by strong magnets. These substances are called paramagnetic. Substances that are slightly repelled by magnets are diamagnetic. Table salt, mercury, zinc and gold are diamagnetic substances.
Substances that are already magnetized are called magnetite. These are called natural or permanent magnets. Lodestones are permanent magnets. Materials that can be made into magnets are called artificial magnets. Artificial magnets are made by induced magnetism. This is done by stroking ferromagnetic materials in the same direction several times with a magnet. This process is called magnetization. ALNICO magnet is permanent magnet containing al uminum, ni ckel and co balt. Temporary magnets are those of soft iron that are easy to magnetize and loses their magnetic property very easily. Electromagnet is an example of temporary magnet. It is a magnet that can be switched on and off. It is used to lift heavy objects in industrial sites and forwarding businesses. Permanent magnets are used in radio speakers, audio-video devices and other electrical appliances.
B. Magnets and Magnetic Forces
Look at the pictures above. The areas of greatest magnetic force are called magnetic poles. Every magnet has two poles. You cannot produce a magnet with only one pole. The end of the magnet that points north is called the north magnetic pole, (N pole), and the end that points south is the south magnetic pole, (S pole).
Like poles repel. Opposite poles attract.
The diagram below illustrates a bar magnet that is suspended by a string. Another bar magnet is brought near it. Study the arrows in the diagram.
The N pole of a magnet is brought near the S pole of the suspended magnet
The S pole of a magnet is brought near the S pole of the suspended magnet
The S pole of a magnet is brought near the N pole of the suspended magnet
The N pole of a magnet is brought near the N pole of the suspended magnet
Rules of Magnets
The diagrams below illustrate the rules of magnets. Refer to the diagrams below:
Uses of Magnets There are also five elements that can be made into magnets: iron, cobalt, nickel, aluminum, gadolinium and dysprosium. None of these elements can be magnetized permanently. To make a permanent magnet, you need an alloy. An alloy is a mixture of two or more metals. The classic material for making a permanent magnet is steel, an alloy of carbon and iron. The best material for permanent magnet is magnequench , which was invented in 1985. This material is mostly iron, with a little neodymium and boron added.
The closer you bring two magnets together, the stronger the force between them becomes. Move them apart and the force gets weaker. If you move them apart farther, you will eventually feel no force. The force changes strength as you move within the magnet’s magnetic field. A magnetic field is the space around a magnet in which its force affects objects. A good picture of a magnetic field can be made by sprinkling iron filings around a magnet. (See figure below.)
Figure A: Figure B:
The magnetic field changes the filings into little magnets that attract one another. This makes the filings form long and thin chains. The chains line up in the shape of the magnetic field.
Figure A shows the magnetic field around a bar magnet. The arrowheads show the direction of the magnetic lines of force, which come out of the N pole and enter the S pole. The concentration of lines of force at the poles shows that the field is strongest there.
Figure B shows the magnetic field around a U-shaped magnet. The shape crowds the lines of force together in between the two poles. This means that the magnetic force between the poles becomes very strong. This is also the reason why a horseshoe magnet can lift greater weights than a bar magnet.
Figure A: Bar magnet
Figure B: U-shaped magnet
(a) between two unlike poles (b) between like poles
Electromagnetism What did you do today? Did you listen to a recorder? Did you use or hear a motor at work in a mixer, blender, refrigerator, washing machine, hair dryer, fan, and vacuum cleaner? Did you hear a buzzer or doorbell sound? What about a cellular phone? If you saw or heard these devices or machines, you observed the combined effects of electricity and magnetism at work. Scientists learned how to use the relationship between electricity and magnetism to produce electric currents and to make machines that would make these devices function. These scientists and inventors have made amazing changes in the way you live.
A. Electricity Makes Magnetism On the morning of February 16, 1820, an important discovery was made by accident. Professor Hans Christian Oersted in Denmark was giving a lecture on electricity to his students. He closed a switch to demonstrate the flow of current. There happened to be a compass nearby. Every time the professor closed the switch, the compass needle turned. Oersted had discovered that an electric current is surrounded by a magnetic field.
( a) ( b)
Figure C: Magnetic Lines of Force
Hans Christian Oersted
This diagrams showed that electricity is produced in a wire as it moves through a magnetic field. It also shows that the direction in which the coil moves affects the direction of the current. The conducting material like the coil cuts the magnetic lines of force that produce electric current.
If we moved the magnet in and out of the magnetic field, is there a current produced? Yes, the effect is the same, but if the magnet does not move, no current is produced, because no magnetic lines of force exist.
Michael Faraday concluded that when a wire is moved through a magnetic field, a current is generated in the wire. This process of generating current by the relative motion between a wire and magnetic field is called electromagnetic induction.
Applications of Electromagnetic Induction What is the difference between the generator and a motor?
1. What is a generator?
A generator operates on the principle of electromagnetic induction. A generato r is a device that converts mechanical energy to electrical energy. It consists of a u-shaped magnet that produces magnetic field, and insulated loop of wire. The wire loop is attached to a power source placed between the magnetic poles. The power source slowly begins to rotate the wire clockwise. As the wire loop moves, it cuts through the magnetic lines of force that induce current. As the rotation of the wire loop
Michael Faraday
MAGNET
COIL
COMMUTATOR
BRUSHES SHAFT
continues, it moves parallel to the magnetic lines of force. When the wire is in this position, no lines of force are cut, therefore, there is no electricity. As it moves further clockwise, the lines of force are cut again producing electricity. The alternate movement of the wire causes alternating current. A rectifier changes alternating current into direct current.
A moving loop cuts through a magnetic field, which generates current in the wire.
Types of Generators
An A.C. generator is a rotating loop in a magnetic field which generates current that fluctuates in value and changes direction every half-rotation of the loop. The current produced is called alternating current (A.C.) A simple D.C. generator is a rotating loop in a magnetic field which generates current that fluctuates in value but does not change direction. The only difference between the simple A.C. and simple D.C. generator is the commutator used. An A.C. generator makes use of two slip rings while a D.C. generator makes use of a split ring commutator.
2. What is a motor?
One of the most important uses of electromagnetism is in the electric motor. An electric motor is a device that converts electrical energy to mechanical energy. A motor contains a movable electromagnet. If an alternating current is supplied to the electromagnet, its poles are reversed. Where it was once attracted by the opposite pole of fixed magnet, it will next be repelled. This process is repeated many times each second.
There are many types of electric motors. Each is designed for a particular purpose or use. They all operate on the principle of electromagnetism.
Electric Code
Electric Outlet
Electricity at Home Human lifestyles have changed. Years ago, most people thought of electricity as little more than a curiosity for amusing people. Too many scientists, however, it was a phenomenon to be studied in the laboratory. Today giant towers across the country carry electricity to every corner of the land. Electricity has become indispensable to our way of life. Look around your home. You will find electric outlets in nearly every wall. This is where electrical appliances are plugged in order to function. You use electricity in many ways.
A. Household Circuits When a house is built, an electrician must install electric outlets, wall switches, fuses, and circuit breakers. All of these devices must be connected by wires inside the walls. In one kind of installation, the wirings in the walls consist of plastic insulated cable. This type of cable is a group of three wires enclosed in a plastic casing. One wire, insulated with its own black cover, is the “hot” wire. This carries the alternating current to the outlet of 220 volts. Caution: DON’T TOUCH THIS WIRE! When touched, it would produce a potential difference of 220 volts that would be very dangerous. This could send enough current through your body to stop your heart from beating. The white insulated wire has no potential but it carries the AC ( alternating current ) back out of the appliances and it might be dangerous to touch. The third wire has no insulation. This wire is connected directly to the ground and it carries no current. This wire is a safety feature.
WHITE WIRE – (grounding)
The electric cable is used to carry electric current to homes and other buildings. The electric outlet, the figure at the left side, is where you insert a plug. The flat prongs are connected to the black and white wires of the cable inside the wall. Current flows in one prong, through the appliance, and back into the wall through the other prong. The potential difference between the prongs causes current to flow, delivering energy to the appliance. The round outlet is a provision for the round prong that serves as the ground wire. If you live in an older type of house, the outlets may not have the grounding terminals.
THIRD WIRE
HOT WIRE
BLACK
B. Short Circuits The 220-volt “hot” wire is very dangerous. Worn insulation or a poor connection can create a short circuit. A short circuit is any accidental connection that allows the current to go directly to the ground instead of passing through an appliance. A 220- volt potential difference can provide any enormous current if there is no appliance in the circuit to provide resistance. A short circuit can cause wires to carry more current than they were designed to carry. The wires can overheat and cause fires.
In modern homes, the ground wire in the cable protects people against short circuits. The metal shell of an appliance is connected to the ground wire through the round, third terminal of the plug. If the “hot” wire touches the shell, the current goes directly to the ground through this lowest – resistance path. If you touch the shell of the grounded appliance, very little of the current will go through your body. Appliances that have plastic shell insulate the user from the current. Such appliances do not need to be connected to the ground.
C. Overloads Have you ever plugged several appliances into the same outlet? If you have, you may have overloaded the circuit. Wires may contain too much current when they are overloaded. An overload may cause the circuit to heat up and melt the wires, much as a short circuit would. Often, this kind of overload occurs in the kitchen. For this reason, kitchens are usually wired with thicker wires that carry more current without overheating. Why are kitchens likely places for circuit overload?
D. Protecting the Circuits
To prevent wire from overheating, circuits are protected against overloads and short circuits. This protection is often provided by a fuse. A fuse is a device containing a short strip of metal with a low melting point. If too much current passes through the metal, it melts, or “blows”, and breaks the circuit. This is your signal to find and correct the overload and to replace the fuse.
Another device that protects circuit from overloads is a circuit breaker. One type of circuit breaker is a switch attached to a bimetallic strip of metal. When the metal gets hot, it bends, which opens, or “trips”, the circuit. This action does not harm the circuit breaker. After the problem has been corrected, the circuit breaker can be reset.
Circuit Breaker
Name: ______________________________________ Date: _________
Grade/Section: _______________________________ Score: _________
Title of the Activity: Let’s Be Magnified!
Directions: Answer what is required. Write your answer on the space provided.
A. Test your understanding by completing the blanks.
- The black metallic ore that has the property of attracting pieces of iron are called. _____________.
- The natural force of attracting pieces of iron is called ___________.
- The word magnet was believed to have been derived from the name of a shepherd named ______________.
- Lodestone was later called ____________ for its magnetic property.
- _________ was a Greek philosopher who first discovered the magnetic property of lodestone.
B. Arrange the jumbled letters to form the word(s) that best fits the statement. Statement/Phrase Jumbled letters Answer
- Natural magnets (^) COILAN
- Clusters of many atoms that act as tiny magnets in a material
MAINODS
- A region around a magnet (^) SFILEDGENAMICT
- Imaginary lines that represent magnetic field
SLIENSOFGENTMIC
FOECR
- Materials that are strongly attracted to magnet GENTAMICORREF
- Materials that are repelled by magnet
GENTAMICIAD
- Materials that are slightly attracted by magnet
GENTAMICARAP
- A substance that possesses magnetic properties
NETGAM
- Iron and other elements can become strongly magnetized
NETGAMITAZIONT
- A magnet has two SLOPES
Title of the Activity: DIAGRAM ANALYSIS: Let’s Trace It!
Directions: The diagram below illustrates a bar magnet that is suspended by a string. Another bar magnet is brought near it. Study the arrows in the diagram and answer the questions below. Write your answer on the space provided.
Answer the following questions:
- What happens to the suspended magnet when the S pole of the other magnet is brought near its N pole?
- What happens to the suspended magnet when the N pole of the other magnet is brought near its N pole?
- What happens to the suspended magnet when the N pole of the other magnet is brought near its S pole?
- What happens to the suspended magnet when the S pole of the other magnet is brought near its S pole?
- How is power distributed from the power plant to the consumer?
- Why is power transmitted at high voltage and low current through long distance?
- To decrease power loss, transmission lines must have low resistance. What materials are used as transmission lines?
- Transmission lines are large diameter wires made of several stranded thinner wires. Why are they made this way?
References
Books:
Alternative Delivery Mode Learning Resource Standards prescribed by the Department of education Central Office. 2020
Department of Education Central Office. Most Essential Learning Competencies (MELCs). 2020.
Hewitt, P.G. Conceptual physics. USA: Addison-Wesley Publishing Co., Inc. 1997.
Navasa, D. and Valdez, B.J. Physics. Quezon City: Sibs Publishing House, Inc. 2001.
Salmorin, L.M. and Florido, A. Physics IV. Quezon City: Abiva Publishing House, Inc.
See Tho Weng Fong Science for Secondary Schools. Singapore: Longman Singapore Publishers. 1995.
Santos, G.N C. and Ocampo J.P. RBS Science and Technology Series E-Physics IV. Sampaloc, Manila. Rex Book Store Inc. 2003.
Taffel, A. Physics: Its methods and meanings. USA: Prentice Hall Publishers.1992.
Tan, M TIMSS-LIKE Test Items in Science and Mathematics. DOST-SEI, UPNISMED, Pundasyon Para sa mga Guro ng Agham at Matematika, Ink.
Tillery, B.W. Physical science. Singapore: WCB McGraw-Hill. 1999.
