Danyal Education. Magnetism. ffil f'r"ts to Know. .a(

Transcription

1 Magnetism d{:.l ffil f'r"ts t Knw,-\rlr-* Q: tate the prperties f a magnet.. magnet attracts magnetic materials such as irn, cbalt, nickel and sme ther allys such as steel.. magnet has tw ples, the rth-seeking ple (-ple) and the uth-seeking ple (-ple). When suspended freely, -ple always pints twards the nrth and the -ple always pints twards the suth.. Like ples repel and unlike ples attract. Q: Describe induced magnetism.. nduced magnetism is the temprary magnetisatin f a magnetic material when it is placed near t r in cntact with a magnet. t is the prcess f inducing magnetism in a magnetic material. Q: Distinguish between magnetic and nn-magnetic materials.. magnetic material is ne, which can be magnetised and is attracted t magnets. ll magnetic materials cntain irn, nickel r cbalt. Fr eample, steel is mainly irn.. nn-magnetic material is ne, which cannt be magnetised and is nt attracted by magnets, which include metals, such as brass, cpper, zinc, tin, aluminum, as well as nn-metals. Q: Draw the magnetic field pattern arund a bar magnet and between the ples f tw bar magnets. tl( )).a( 155 Chapter 19 Magnetism

2 Q: Describe electrical methds f magnetisatin and demagnetisatin.. Magnetisatin: cil made up f cpper wire is cnnected in series with a battery. The steel bar, which is t be magnetised, is inserted int the cil. direct current flws thrugh the cil and a magnetic field is prduced arund it. The magnetic field will magnetise the steel bar. a teel ar Demagnetisatin: magnet is inserted int a cpper cil. n alternating current flws thrugh the cil. When the magnet is withdrawn slwly frm the cil, the magnetic field arund the cil causes the magnet t lse its magnetism. This happens because the magnet is cnstantly being magnetised in ppsite directin by the alternating current. s the magnet is being slwly withdrawn frm the cil, the diples in the magnet will be arranged different directins, cancelling their magnetic effect bar ----) Pull ut slwly ) -> ) <_ ----,7 156 Chapter 19 Magnetism t

3 Q: Describe the pltting f magnetic field lines with a cmpass. pparatus: ar magnet, pltting cmpass, plain paper Z. 1 a jx Prcedure: l. Place the bar magnet at the centre f the piece f paper s that its rth ple faces nrth and its uth ple faces suth. 2. Place the cmpass near ne ple f the magnet, and mark with pencil dts and label the psitins f the ends, and, f the cmpass needle and X. 3. Mve the cmpass until ne end f the cmpass needle is eactly ver mark and mark the new psitin f the ther end with a third dt Z. 4. Repeat the abve until the cmpass reach the ther ple f the bar magnet. Jin the series f dts and this will give a field line f the magnetic field. Use this methd t plt ther field lines n bth sides f the magnet. 5. ndicate the directin f the magnetic field lines as given by the cmpass needle. Q: Distinguish between the prperties and uses f temprary magnets and permanent magnets.. Temprary magnets are made frm sft magnetic materials such as irn. They can be magnetised and demagnetised easily. They can be magnetised by a weak magnetic field and are used in electrmagnets, transfrmer cres and magnetic shields.. Permanent magnets are made frm hard magnetic materials such as steel. Hard magnetic materials are harder t magnetise and demagnetise. They have the ability t retain their magnetism and are used t make permanent magnets such as the needle f a pltting cmpass. 157 Chapter 19 Magnetisn

4 ffiprblems t lve steel bar is being strked by a bar magnet and an irn bar is inserted int a slenid as shwn belw. a. tate the plarities at X and. (1mark) b. tate the plarities at P and Q. (1mark) c. Which bar is used as a permanent magnet? Eplain yur answer. ( 2 marks ) d. The irn bar is taken ut frm the slenid and place clse t the steel bar as shwn belw. Eplain what will happen t the tw bars. ( 3 marks ) P a P a 158 Chapter 19 Magnetisn

5 2. pltting cmpass is separately mved slwly twards three metal bars alng paths l, 2 and 3. The final psitins f the cmpass needle are as shwn in the diagram belw. ar X \ r r ar 2 2 <F v. --- path 1 a. What can yu cnclude abut bar X based n the diagram abve? Eplain yur answer. ( 3 marks ) b. What can yu cnclude abut bar based n the diagram abve? Eplain yur answer. ( 4 marks ) c. What can yu cnclude abut bar Z based n the diagram abve? Eplain yur answer. ( 4 marks ) path2 zl c ry t ar Z path 3 Z^ 159 Chapter 19 Magnetism

6 Miscnceptins t Clari$ Which f the fllwing crrectly shws the directins f the pltting cmpasses placed arund a bar magnet? C D 2. Which f the fllwing is the best way t demagnetised a magnet using the heating methd? Heat the magnet in biling water and allw it t cl in the rth-uth directin. Heat the magnet in biling water and allw it t cl in the East-West directin. C Heat the magnet t becme red ht and allw it t cl in the rth-uth D Heat the magnet t becme red ht and allw it t cl in the East-West directin. 3. The diagram belw shws a pltting cmpass placed abve a cpper wire when there is n current flwing in the wire. 4 What is the directin f the cmpass needle when a large direct current flws frm pint t pint?.' C1 E DJ The diagram belw shws a pltting cmpass placed abve a cpper wire when there is n current flwing in the wire. ( ) What happens t the cmpass needle when a large alternating current flws frm pint t pint? The cmpass needle pints twards the right. The cmpass needle pints twards the left. C The cmpass needle scillates left and right. D The cmpass needle spins in circular mtin. ( ) 160 Chapter 19 Magnetisn

7 5. Which f the fllwing cnectly shws the directin f the pltting cmpasses when current flws frm X t? {- C D t6t Chapter 19 Magnetism