Waves and
Physics Grade 10 Advanced level-895350233680 Electrostatics and magnetismContents-323850-228600 UNIT 6: Electrostatics and magnetism-476250154305-890270353695Core Standards …………………………………..… 3 Objectives ………………………………..………… 430.1- Electrostatics ………………………………..……………………… 530.2 Friction and charge ………………………………..……………. 830.3 Electric Field ………………………………..…………………….. 1930.4 Magnetism ………………………………..……………………….. 2530.5 Magnetic Field ………………………………..…………………… 32-37465085090 Questions ………………………………..….……… 35-46672512700 References ………………………………..…..…… 394659289-211540-151547-21154010A.30.1 Distinguish between conductors, semiconductors and insulators with reference to moving electrons or ions; know how the properties of semiconductors can be influenced by the presence of small quantities of impurities.10A.30.2 Know that friction can generate two kinds of electric charge on an insulator and that opposite charges attract but like charges repel each other.10A.30.3 Describe an electric field as an example of a field of force and know that electric field strength can be defined as force per unit positive charge and that an electric field can be represented by means of field lines.10A.30.4 Make magnets from magnetic materials by a variety of methods. Know that they have north and south poles and that unlike poles attract and like poles repel each other.10A.30.5 Describe a magnetic field as an example of a field of force and know that it can be represented by means of field lines.-215265-4572004526915-457200By the end of the unit, students generate electrostatic charge in insulators, know the rules of electrostatic attraction, know how to use an electroscope to investigate charge and understand distribution of charge on a conductor. They detect electric fields and know that they can exert a force on a charge They know that magnets have north and south poles and generate fields, the shape of which they plot, that exert forces on other magnets.Students who progress further define electric field strength and draw and interpret field lines representing the strength and direction of electric and magnetic fields.30.1Electrostatics???????? ???????Lighting is a common occurrence during a heavy rain. Have you ever wondered how lighting is produced and why it is usually strikes during a heavy rain?????? ????? ???? ?? ?????? ??????? ??? ???? ??? ???? ??????5038725234950 Some Common Phenomena of Static electricity4000500494665Have you ever placed your hand next to a television screen when the television has just been switched on? The hair on your hand will stand on end.?? ???? ???? ???? ???? ???? ??? ?????? ??? ????? ??????? ???? ???????4000500459105Try walking across a rug and reaching for a doorknob in a dry environment. You will experience a shock!???? ??? ???? ????? ?? ??? ??? ??? ????? ??? ????? ????.????? ?????? ?????.30.2Friction and charge???????? ???????Some objects (such as a glass rod or an ebonite rod) acquire a new property of being able to attract small pieces of paper after they have been rubbed with another material (such as silk or fur). This phenomenon belongs to the branch of Physics called electrostatics or static electricity. It involves the study of static electric charges. Before rubbing, these objects do not attract small pieces of paper. This implies that friction due to rubbing has changed the nature of the surfaces of the rods. We say that friction has caused the rods to be 'electrified' or 'charged'.??? ?????? ????? ?? ???? ????? ??? ?????? ?? ????? ??? ???? ????? ?? ?????? ?? ?????. ??? ???? ??????? ????????? ???????. ??? ??? ??????? ?? ???? ??? ?? ???? ?????? ?????.??? ???? ?? ???????? ????? ????? ??? ??? ?????? ?????? ????????. Some electrostatic experimentsTable gives a summary of some electrostatic experiments and the corresponding observations and inferences. ??? ????? ???????? ??????? ?????????? ????????????. ExperimentObservationsInferencesExperiment 1The pith ball remains in its rest position when the uncharged glass rod is brought near to it.???? ??? ???????? ????? ??? ????? ???? ?????? ??? ??????? ????.The gravitational force of attraction between the pith ball and the uncharged glass rod is too weak to cause any movement in the pith ball.??? ??????? ?????? ????? ??? ???? ?? ???? ???? ?????.1. For Experiment 2, the pith ball is seen to move towards the glass rod after the rod has been rubbed with silk???? ????? ?????? ?????? ??? ???? 2. For Experiment 3, the pith ball is seen to move towards the ebonite rod after the rod has been rubbed with fur.3. The angles of displacement θ1 and θ2 of the pith ball are generally large??????? θ1 and θ2 ????? ???? ???? ?????.1. Both the glass and ebonite rods are able to attract light objectsafter they are rubbed with silk and fur respectively, i.e. they are electrified or charged.???? ???? ?????? ??? ???? ??????? ????? ??? ????????.2. The attraction between the pith ball and each rod is fairly large, i.e. the electrostatic force is much stronger than the gravitational force between the pith ball and the rods.??? ??????? ??????? ???? ?? ??? ??????? ??????.The angle of displacement of the pith ball θ3 is smaller than θ1 or θ2,??????? θ3 ???? ????? ?? ????????? θ1 ?θ2The electrified states of the glass and ebonite rods tend to weaken each other. In other words, there exist twoelectrified or charged states.???? ????? ?????? ????????? ????????? ??? ????? ?????? ?????.The two charged glass rods are seen to repel each other. (Note: Repulsion also occurs between two chargedebonite rods.)???? ????? ?????? ???? ???????.The electrified glass rods have similar or like charges.????? ????? ?????? ??????.The two charged rods are seen to attract each other.???? ????? ??? ????????. The glass rod and ebonite rod have different or unlike charges.????? ???????? ??????.4743450208280Based on the results of the experiments in Table we can conclude that: ??? ??????? ?? ??????? ???????.Friction produces two different kinds of charges on different materials (Such as glass and ebonite) .1- ???????? ???? ????? ?????? ??? ??? ???? ??????. Like charges always repel each other. And unlike charges always attract each other.2- ??????? ???????? ?????? ????????? ??????Only two kinds of charges exist. 3- ???? ????? ?? ???????.An explanation of charging by friction????? ????? ?? ???? ????????Matter is made up of indivisible particles called atoms. Each atom has negatively-charged electrons orbiting round a small massive nucleus which consists of positively-charged particles called protons and neutral particles called neutrons. Figure shows an atomic model of a beryllium atom.?????? ????? ?? ???? ????? ????? ????? ?? ??????????? ???? ??? ???? ????? ???????? ????? ?????????? ???????In charging by friction (such as rubbing a glass rod with silk), some electrons from the surface atoms of one object (the glass rod, in this case) are transferred to another object (silk, in this case). This makes the glass rod positively charged as it is now short of electrons. The silk becomes negatively charged as it gains excess electrons. Charge is never made or destroyed in the friction process; it is transferred from one material to another.??? ??? ?????? ??? ??????????? ????? ?? ???? ????? ??? ???? ?????? ???? ?????? ????? ??????????? ????? ????? ?????? ???? ??????????? ?????. ??? ??? ???? ?????? ????? ??????? ????????? ????? ?????? ????? ????????? ?????????.??????? ?? ???? ?? ???? ????? ????? ?? ???? ?????.The Table summarizes the charges produced on some common materials due to the friction process.?????? ?????? ???? ??? ?????? ??? ?? ???? ??? ????? ???????.MaterialsPositive chargeNegative chargeGlass rod rubbed with silkGlass ???? Silk ???? Ebonite rod rubbed with furFur??? Ebonite ??????? Perspex ruler rubbed with woolen dusterPerspexDuster ???? Plastic comb rubbed with hairHair ??? Plastic combPolythene strip rubbed with woolen dusterDuster Polythene ?????? Unit of charge???? ?????? ???? ?????? The SI unit of charge is the coulomb (C). It is equal to the charge on about 6 million million million electrons, although it is not defined in this way. One coulomb is a relatively large quantity of charge, and it is often more convenient to measure charge in microcoulombs: 1 microcoulombs (?C) = 10-6 Cthe charge on a rubbed polythene rod is, typically, only about 0.005 ?C. ?????? ??????? ?????? ?? ???????. ??? ????? ????? 6 ????? ????? ????? ???????. ?????? ?? ???? ???? ???????. ??? ????? ???? ??? ??? ?????? ???? ???????????? . ?????? ??? ??? ???????? ?????? ????? 0.005 ??????????.Conductors and InsulatorsWhen some materials gain charge, they lose it almost immediately. This isbecause electrons flow through them or the surrounding material until thebalance of negative and positive charge is restored.Conductors????? ????? ??? ?????? ???? ? ????? ?????? ????? . ??? ???? ?? ??????????? ????? ???? ?????? ??? ?????? ?????? ??????? ??????? ???????. 421957529845 are materials that let electrons pass through them. Metals are the best electrical conductors. Some of their electrons are so loosely held to their Atoms that they can pass freely between them. These free electrons also make metals good thermal conductors. Most non-metals conduct charge poorly or not at all, although carbon is an exception.???????? ?? ???? ???? ??????????? ??????? ??????. ??????? ????? ???? ???????? ????????? ??? ????????? ????? ???????? ?????? ??? ????? ????? ??? ??????. ??????? ??? ???????? ??? ????? ??????? ?? ??? ????? ???????? ???????. Insulators4133850-95250are materials that hardly conduct at all. Their electrons are tightly held to atoms and are not free to move - although they can be transferred by rubbing. Insulators are easy to charge by rubbing because any electrons that get transferred tend to stay where they are.???????? ?? ???? ?? ???? ??????????? ??????? ?????? ??? ??????????? ?????? ???? ???????. ?????? ???? ?????? ??? ????? ??? ??????????? ???????? ???? ?????? ??? ??. Semiconductors413385018415These are 'in -between' materials. They are poor Conductors when cold, but much better conductors when warm.????? ???????? ?? ??? ???????? ????????? ????? ???? ?????? ??? ??? ???????.Charging conductors by induction??? ???????? ????????Induction is the process of charging a conductor without any contact with the charging body. ????? ???????? ???????? ??? ??? ?????? ????? ??????? ????? ?????To charge two conductors with equal and opposite charges:?- ??? ?????? ??????? ???????? ?????????.-161925158115 Step 1: The two conductors (metallic spheres) on insulator stands are brought into contact with one another (Figure 1) ?????? ??????? ??? ????? ????? ?????????. -475615254635-161925-92710Step 2: A negatively-charged rod is brought near to sphere A (Figure 2) . This causes the electrons from A to be repelled to the farthest side of sphere B. Under this condition, sphere A alone will have excess positive charge (due to electron loss) while B alone has excess negative charge (due to gain of electrons). ???? ???? ????? ??????? ?? ?????? A ??? ???? ?????? ??????????? ??? ???? ???? ?????? B ????? A????? ??????? ????????? ?B????? ???????? ?????????.-161925131445Step 3: With the negatively-charged rod in place, the two spheres A and B are separated a distance apart using the insulating stands (Figure 3)????? 3 ???? ???????? ???????? ?????? ?????? ????? ?????? ??????? ???????30162529210-151765-200025 Step 4: The sphere A will now have induced positive charges while B will carry an equal number of induced negative charges. The charge on the charging rod remains unchanged (Figure 4) . ??? ????? ?????? ??????? ???? ??? ?????? ??????? ?????? ??????(b) To charge a single conductor by induction.?- ??? ???? ???????? . -6667527305-561340699135Step 1: Bring a charged rod (say positively charged) to the vicinity of the conductor held by an insulating stand (Figure 1) .???? ???? ???? ?????? ?? ???? ???? ????? ????3810074930Step 2: The free electrons in the conductor will be drawn towards the end of the conductor nearer to the positively-charged rod. Leaving the other remote end to have excess positive charge. Note that the conductor is still electrically neutral despite the redistribution of the free electrons on it (Figure 2).????? ??????????? ????? ?????? ?????? ???? ?????? ????? ????? ????? ?????? ???? ??????? ?????? ?????? ???? ?????? ?????? ??? ????? ?? ????? ????? ??????????? ????? ????. -267970114300Step 3: With the positively-charged rod still in place, the conductor to be charged is earthed. This can be done by touching the conductor with our body momentarily. Being a relatively good conductor, our body will allow electrons to flow to the conductor to neutralize the excess positive charge on the far side of the conductor. Note that now the conductor will carry an excess negative charge (Figure 3).????? ?????? ??????? ???? ?????? ??????? ???? ???????? ????? ????? ????? ????? ????? ????????? ??? ?????? ?????? ??????? ??????? ????? ?????? ????? ?????? ????? ???.75247574930-15113091440Step 4: On removing the charging rod, the excess negative charge (electrons) will redistribute on the surface of the conductor to attain electrostatic equilibrium (Figure 4) ?????? ?????? ??????? ???? ?????? ???? ??????? ??? ????? ??????????? ??? ???? ????? ??????? ???????????????. Note also that charging a single conductor by induction will always result in a charge that has the opposite sign to that of the charging rod.?????? : ?????? ?????? ??????? ???? ???? ?????? ??? ???? ??????.Electroscope?????? ??????? (Figure 1&2) shows the structure of a typical electroscope used for thedetection of charges and to test for the sign of the charge.????? ???? ????? ?????? ??????? ???? ?????? ?????? ?? ??? ????? ????? ?? ?? ????? ??? ?????? ?? ??? ??????.11239501885951638300260985Detection of charge?- ????? ?? ???????In Figure 3, the gold leaf is close to the brass plate. It is in a collapsed state. The brass cap, brass rod, brass plate and the gold leaf are electrically neutral (there is no excess charge).-952506330953400425575945?? ????? 3 ?????? ??????(???????? ????????? ?????????? ??????? ???????? ?????? ??????? ????????? ????????? ?????? ??????? ?????? When a charged insulator (such as a positively-charged glass rod) is brought near to the brass cap, the free electrons from the brass and gold parts of the electroscope are attracted to the brass cap, leaving the brass plate and gold leaf positively charged. This causes the gold leaf to diverge due to the repulsion between like positive charges (Figure 4). In this way, we can conclude that the glass rod is charged.?????? ???? ????? ??????? ?? ????? ??????? ?????? ????? ??????????? ????? ??? ????? ??? ????? ?????? ????????? ??????? ??? ???? ????? ???????? ????? ???? ?? ?????? ??? ??????.(b) Testing for the sign of charge ?- ????? ?? ??? ??????To test for the sign of a charge on a charged body, we need to charge the electroscope first. The electroscope can be charged easily by induction. The following diagrams show the sequence of charging the electroscope positively by induction (Figure 5).-28575771525????? ?? ???? ??? ?? ????? ???? ?????? ???? ?????? ????????. ??????? ??????? ???? ??? ?????? ????? ????? ????????.37147503486785????? 5 ???? ????? ??? ?????? ??????? ????? ?????.To charge the electroscope negatively, we can slide a negatively-charged rod on the brass cap of the electroscope (Figure 6) so that some electrons from the charged rod can be transferred to the cap causing the gold leaf to deflect or diverge.????? 6 ???? ??? ?????? ????? ?????. ???? ??????? ??? ????? ???? ?????? ??? ?? ??? ??????????? ????? ????? ????? ???????? ????????? ???????.Negative charge detection????? ?? ???? ????? 367665062865If a charged rod with an unknown charge is brought near to a negatively charged electroscope and there is an increase in the divergence of the gold leaf, we can conclude that the charge on the charged rod is negative (Figure 7).??? ????? ??? ????? ?????? ?? ???? ????? ??????? ???? ?????? ???????? ????????? ??? ????? ???? ????? ???????.Positive charge detection????? ?? ???? ????? Similarly if a charged rod is brought near to a positively-charged electroscope and the divergence of the gold leaf increases, we can conclude that the charge on the charged rod is positive (Figure 8). Note that for both cases of testing the sign of the charge, only the phenomenon of repulsion between like charges is used. Do you know why attraction between unlike charges cannot be used to test the kind of charge?3333750163830??? ????? ??? ????? ?????? ?? ???? ????? ??????? ???? ?????? ???????? ????????? ??? ????? ???? ????? ???????.( ????? ?? ???????? ??????? ????? ??????? ??? ???????? ??? ?????? ???? ??????? ?????? ??? ?????? ???? ????? ???)Electric Field ?????? ??????? 30.3Michael Faraday developed an approach that helps us both understand and calculate the influence of a charged particle on other charged particles??? ??? ??????? ?????? ????? ??????? ??? ????? ????? ???????? ???????? ??? ????? ?? ????????This approach is called the field concept ??? ??????? ?? ?? ???? ????? ?????? We say that a charged particle creates a field throughout all of space???? ???????? ???????? ?????? ???? ????? ???? ?????? ????? ?? ???????? ???????? ???????Other charged particles then interact with this field4419600429260Here a charge Q sets up a field that points away from the charge in three-dimensional space. ?? ??? ????? ???? ???? ?? ????? ???? ?????? ???? ??? ????? ?? ?????? ???????.If we place a test charge at point P, we can measure the field at that point by looking at the force exerted on the test charge by the field.??? ??? ???? ???????? ??? ?????? ( P) ?????? ???? ????? ?????? ??? ??? ?????? ?? ???? ????? ??????? ??? ?????? ??????????.We bring in a positive charge q0 as a test charge, which is carefully selected with a very small magnitude, so that it does not alter the locations of the other charges1743075237490The electric field E that exists at a point is the electrostatic force F experienced by a small test charge q0 placed at that point divided by the charge itself:??? ????? ???? ???????? ????? ???? qo ?? ???? ????? ??? ?????? ??????? ??? ??? ?????? ????? ????? ???????? ??????? ???????? ??????? ?????????? ????? ??? ????? ??? ?????? .1739265106680The electric field is a vector, and its direction is the same as the direction of the force F on a positive test charge ?????? ??????? ?? ???? ???? ????? ?????? ?? ??? ????? ????? ??? ?????? ?????????? ??????? SI Unit of Electric Field: Newton per coulomb (N/C) Important about electric field????? ?? ?????? ??????? It is the surrounding charges that create an electric field at a given point.???? ?????? ??????? ??????? ???????? ?? ??? ??????.Any charge q placed at the point with the electric field E will experiences a force, F=qE. For a positive charge, the force points in the same direction as the electric field; for a negative charge, the force points in the opposite direction as the electric field. ?? ???? ?????? ?????? ?? ???? ????? ?????? ???? ???? ???????? ??????? ?????. ???????? ?????? ??????? ??? ????? ???? ?? ??? ????? ?????? ??????? ??? ??? ?? ???? ?? ?????? ???????.At a particular point in space, each of the surrounding charges contributes to the net electric field that exists there3114675645795161290665480?? ???? ?? ?? ?????? ? ?? ???? ????? ????? ?? ?????? ??????? ????? ??????? ?? ??? ??????.Example?: Electric Field Leads to a Force???? : ?????? ??????? ???? ??? In Figure a the charges on the two metal spheres and the ebonite rod create an electric field E at the spot indicated. This field has a magnitude of 2.0 N/C and is directed as in the drawing. Determine the force on a charge placed at that spot, if the charge has a value of (a) qo=+18×10–8 C and (b) qo =–24×10–8 C.?? ????? ?????? ??????? ????????? ??? ?????? ???????? ???? ??? ???????? ???? ?????? ??????? ??? ?????? ???????. ????? ??? ?????? ?? 2 ?????/ ????? ??????? ??? ?? ????? . ??? ????? ??????? ??? ?????? ???????? ??? ??? ?????? ??? ???? ?? ????? ?????? ?? ?????? (?) ?? qo=+18×10–8 C ??? ?????? (?) ?? qo=–24×10–8 C752475104140Electric Field Lines ???? ?????? ??????? What does an electric field look like?-152400187960An electric field can be visualized on paper by drawing lines of force, which give an indication of both the size and the strength of the field. Lines of force are also called field lines. Field lines start on positive charges and end on negative charges, and the direction of the field line at a point tells you what direction the force experienced by a charge will be if the charge is placed at that point. If the charge is positive, it will experience a force in the same direction as the field; if it is negative the force will be opposite to the field. ???? ????? ?????? ??????? ???? ???? ????? ????? ???? ???? ?? ????? ???? ?????? ???????. ???? ????? ???? ????? ????? ??????. ???? ???? ?????? ?? ?????? ??????? ?????? ??? ?????? ???????.The fields from isolated, individual charges look like this: ?????? ?????? ?? ??????? ???????? ????????? ???? ??? ??? :When there is more than one charge in a region, the electric field lines will not be straight lines; they will curve in response to the different charges. In every case, though, the field is highest where the field lines are close together, and decreases as the lines get further apart. ??? ??? ???? ???? ?? ???? ?? ????? ????? ??? ???? ???? ?????? ??????? ???? ????? ??? ????? ??????? ??????. ??? ?? ??????? ??? ??? ?????? ??????? ???? ???? ?? ???? ????? ?????? ???? ?????? ???? ????? ?????? ???? ??????.587375104775340233021717024269701031875Rank the magnitudes E of the electric field at points A, B, and C shown in the figure.??? ????? ?????? ??????? ??? ?????? ??????? ??? ??? ?????? A) EC>EB>EA B) EB>EC>EA C) EA>EC>EB D) EB>EA>EC 83820-2885440 E) EA>EB>EC30.4??????????? Magnetism In our childhood, most of us might have come across a few objects that attracted pins, needles, blades, etc. We realized that they did not attract things like paper, wooden blocks, plastic scales, etc. Later, we learnt that such objects belonged to a class called magnets. In this chapter we will study the types and properties of magnets. 2009775714375?? ??????? ???????? ??????? ????? ?? ???? ??? ?????? ????? ????????? ( ??? ???????? ???????? ???????? ) ?????? ?? ????? ?? ??? ????? ??????. ?????? ??? ??? ?? ???? ?????????? ???? ????? ??? ?????.Properties of Magnets???? ??????????? To understand the properties of a magnet, try and do the following:???? ???? ????????? ????? ?????? ??????? ?????? :1. Suspend a bar magnet horizontally with the help of a string.?When you disturb the magnet, you will observe that the magnet starts oscillating. After some time, it comes to rest in the same direction in which it was undisturbed. ?? ?????? ???? ?? ????????? ?????? ?????? ???. ??? ???? ????????? ?????? ?? ????????? ??? ????????? ???? ???? ????? ???????? ?? ??? ??????? ???? ??? ???? ???????? 1543050-20427952.Repeat the experiment. If you watch the magnet’s direction carefully you will notice that the magnet always comes to rest in the earth’s north–south direction. It is one of the inherent properties of magnets. On all bar magnets, the end that points to the earth’s north is called the north pole – it always marked with a white dot. The other end, pointing towards the Earth’s south is called the south pole.?? ?? ??????????? ???????? ???? ????? ???? ???? ??? ????? ??????? ????? ??? ????????? ?? ????? ??????? ????????? ????? ?? ???? ?? ????? ????? ? ????? ????? ?????? ?????? ???????.A magnet’s directional property is used in a mariner’s compass. Keep the compass in any direction; it comes to rest in the north–south direction. The compass has a thin needle pivoted freely and it is made out of a magnet. In ancient times, the compass helped travelers to navigate and know their directions. ???? ????? ????????? ????????? ?????? ?????? ????????. ???????? ????? ?? ???? ????????? ????? ?????? ????? ????? ??? ????????? ??? ????? ?????.We can therefore say that the magnets preferably attract iron and does not attract copper or aluminum. This is known as the attractive property of a magnet.????? ??????? ????????? ??? ??? ?? ???? ???? ????? ????????? ??? ?????? ????? ?? ????? ??? ?????? ???????????3. The iron filings are seen to be attracted only to the ends of the bar magnet. Therefore, it can be concluded that the end regions of a magnet have greater strength to attract iron filings. We call these regions of a magnet – the north pole and the south pole. ????? ????? ?????? ??? ???? ????????? ??? ??? ???? ?? ????? ?????? ????????? ????? ?? ??????? 15335251289054. Take two bar magnets. Try and bring the two like poles together. Then try and bring two unlike poles together. You will observe that north–north poles and south – south poles repel each other. Whereas north – south poles of the two bar magnets attract each other.????? ????????? ????????? ?????? ????????? ?????? ????? ??? ????? ??????:73342565405This rule is similar to the rule for the forces between electric charges, where like charges repel one another and unlike charges attract. But there is a very important difference between magnetic poles and electric charges. Whereas electric charges can be isolated, magnetic poles cannot.??? ??????? ???? ????? ????? ???????? ??? ??????? ???????? ?? ??? ??????? ???????? . ??? ???? ?????? ????? ??? ??????? ???????? ???????? ???? ????? ?? ????? ????? ?? ???? ??? ??????? ??????????? ?? ????? We see that the attraction or repulsion of the poles is observed even if the poles are at a distance from each other. We say that there is a force, a 'actions at a distance' force, that is acting on these magnets. The magnetic poles are experiencing a force due to what we call 'magnetic fields'.13335001165860???? ????? ????????? ???? ??? ??????? ??????????? ??????? ???? ?? ???? ?? ???? ??????? ??????????.30.4Methods of making magnets ??? ????? ????????? ‘Stroke’ method ????? ?????? A piece of magnetic material can be turned into a magnet if it is stroked by a magnet. As the magnet moves along the magnetic material, it causes the magnetic dipoles in the magnetic material to become aligned in one direction and give rise to a magnetic field.???? ????? ???? ?????? ??? ??????? ?? ???? ????? ????????. ???? ????? ???? ?????? ???????? ??? ????? ???? ?????? ????? ?????? ????? ???? ???? ????????.942975182880Electromagnets ????????? ???????Activity???? 952515240To make an electromagnet you may implement the following steps. ?????? ??????? ????? ????? ????? ??????? ???????:Step 1 - Gather the Materials ??? ?????? -438785175260 One iron nail fifteen centimeters (15cm) long???? ?????? ???? 15 ?? Three meters (3m) of insulated, copper wire3 ??? ?? ??? ????? ?????One or more D-cell batteries ?????? ?? ???? ?? ????? ?????? wire strippers ????? ????? -381000617855 Step 2 - Remove some Insulation ????? ????? Some of the copper wire needs to be exposed so that the battery can make a good electrical connection. Use a pair of wire strippers to remove a few centimeters of insulation from each end of the wire.??? ????? ???? ????? ?????? ??? ?? ???? ????? ??????? ??????? -25781074295Step 3 - Wrap the Wire Around the Nail ?? ????? ??? ??????? Neatly wrap the wire around the nail. The more wire you wrap around the nail, the stronger your electromagnet will be. Make certain that you leave enough of the wire unwound so that you can attach the battery.?????? ?????? ?? ????? ??? ??????? ? ????? ???? ??? ?????? ???? ???? ??? ?????????When you wrap the wire around the nail, make certain that you wrap the wire all in one direction. ??? ?? ????? ???? ?? ???? ???? ??? ?? ????? ????.-15113040005 Step 4 - Connect the Battery ????? ???????? Attach one end of the wire to the positive terminal of the battery and the other end of the wire to the negative terminal of the battery. If all has gone well, your electromagnet is now working.??? ???? ???? ????? ??? ????? ?????? ???????? ?????? ????? ????? ?? ??? ???????? ??????.Don't worry about which end of the wire you attach to the positive terminal of the battery and which one you attach to the negative terminal. Your magnet will work just as well either way. What will change is your magnet's polarity. One end of your magnet will be its north pole and the other end will be its south pole. Reversing the way the battery is connected will reverse the poles of your electromagnet.?? ???? ???? ??? ??????? ???? ???????? ( ????? ??????? ) ??? ??? ??? ???? ????? ?????? ?????? ????????? ?????? ? ???? ????? ??????? ???? ????? ????????? ??????? ??????.Magnetic Field ?????? ??????????30.5A magnetic field is an invisible field which exerts magnetic force on substances which are sensitive to magnetism. A classic example of a magnetic field is the field created by an iron magnet; to see how the energy in such a field works, you can place a small magnet under a piece of paper and sprinkle iron filings on it. As the filings respond to the magnetic field, they will slowly orient themselves along an axis. 819150776605?????? ?????????? ?? ???? ??? ???? ???? ???? ????????? ??? ?????? ???????????. ??? ??????? ???????? ?? ?????? ?????????? ????? ???????? ??? ???? ???? ???? ?? ???? ????? ?????? ??? ???? ??? ??????? ??????? ?? ?????? ????? ?????? ??. Magnets are surrounded by magnetic fields. A magnetic field can be thought of as consisting of lines of force. The forces of magnetic attraction and repulsion move along the lines of force. The iron filings line up along the magnetic field lines of the magnet. Note the circular pattern of the field lines. By convention, we say that the field lines emanate from the north pole of the magnet and re-enter the magnet through the South Pole. Note also that the field lines are closer together at the poles than at the center of the magnet. More iron filings are attracted to the poles because the strength of the magnetic field is greater at the poles. Discover the affect on magnetic field lines when two magnets are placed close to each other.?????? ?????????? ???? ?????????? ??? ??? ???? ???? ???? ???? ????? ? ???? ??????? ???????? ????? ?? ?????? ??? ??? ??????. ????? ??? ?????? ????? ???? ???? ?? ????? ??????? ??? ????? ??????? . ????? ??????? ??? ??? ??????? ??????? ???? ?????????, ??? ????? ????? ??? ???? ?? ????? ?????? ??? ??????? . ???? ??? ??? ?????? ?????????? ???? ??? ??????? . ????? ?????? ???? ?????? ?????????? ??????????? ????????. Larger examples of magnetic fields include the Earth's magnetic field,???? ??? ?????? ?????????? ?? ???? ????? ??????????. Earth's magnetic field?????? ?????????? ????? Earth is a huge magnet. For points near earth's surface, its magnetic field can be approximated as the field of huge bar magnet – a magnetic dipole – that straddles the center of the planet. Hence a suspended magnet or compass points northward. The compass aligns with the magnetic field of the earth.438150984885 ????? ????? ??????? ????? ? ?????? ???? ?? ??????? ???? ??????? ????? ?? ????? . ??? ??? ?????? ??????????? ????? ?? ?????? ????? ????? Questions-510806-5740991- The diagrams below show charged and neutral bodies being brought together.??????? ???? ?????? ?????? ????? ??????? ?????? ?? ????? ?????. -438150365125Indicate whether the objects attract or repel each other.??? ?? ???? ??? ??????? ?????? ?? ??????DiagramObservation(a)(b)(c)(d)2. When someone pulls a plastic comb through their hair, the comb becomes negatively charged ??? ??????? ??? ?? ????????? ???? ????? ???? ????? ???? ?????? . a) Which ends up with more electrons than normal, the comb or the hair??? ??????? ????? ????????? ???? ????? ?? ??????b) Why does the hair become positively charged?????? ???? ????? ?? ???? ??????3. On the right, a charged rod is held close to a metal can. The can is on an Insulated stand?? ????? ??? ?????? ?????? ?? ???? ?????? ?????? ??? ???? ???? 1724025217170a) Copy the diagram. Draw in any induced charges on the can.?- ???? ????? ????? ?? ???? ????? ??? ?????? ????????. b) Why is the can attracted to the rod even though the net (overall) charge on the can is zero? ?- ??? ????? ?????? ????? ?? ?? ????? ??????? ????? ?????c) If you touch the can with your finger, electrons flow through it. In which direction is the flow??- ?? ???? ?????? ????? ???? ????? ??????????? ? ?? ?? ????? ???? ??? ??????? d) What type of charge is left on the can after it has been touched??- ?? ??? ?????? ???????? ??? ?????? ??? ????? ?????? 4- If you are given a negatively-charged rod. Describe how you can use it to charge a neutral electroscope positively.??? ????? ??? ?????? ??????? . ?? ??? ???? ???????? ???? ???? ????? ?????? ????? ?????.5- Tow small light balls coated in metallic paint are Suspended by long insulating threads from points A and B as shown below.????? ??????? ???????? ????? ????? ??????? ????? ????? ?????? ??? ????? A ? B ??? ?? ?????.193357527305a- Both balls are given a positive charge. Complete the figure below to show the new positions of the balls and their suspending threads.??? ???? ??????? ????? ????? . ???? ????? ????? ??????? ??????? ??????? ????? ???? ???????.2009775154305b- The ball suspended from B is carefully moved and suspended from C without altering the charges on either of the two balls. Complete the figure below to show the new positions of the balls and their suspending threads. ??? ???? ????? ??????? ? B ???? ????? ?? C ??? ????? ?? ???? ??????? . ???? ????? ????? ??????? ??????? ??????? ????? ???? ???????.19335751022354877435-54610Resources:Books:1-Physics A Course for “ O” level.(Charles Chew. Leong See Cheng) 2- Complete physics (Stephen Pople)3- Essentials of physics (Julie Quah. Chuen Wee Hong)4-Longman GCSE physics (Brin Arnold . Steve Woolley)5- Advanced physics for youWebsites: ................
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