Chapter # 14 Magnetism and Electromagnetism

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CHAPTER # 14 Magnetism and Electromagnetism

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The sources of magnetic field are: a) Isolated magnetic poles b) Charges at rest c) Charges in motion d) None of the above A current carrying straight conductor is placed in a magnetic field perpendicular to it. The forece experienced by the conductor is: a) F = BIL b) F = BIL cos   c) F = BIL sin d) F0 The standard vector symbol for flux density is: a)  b) B c) L d) M Flux density is measured in: a) Webers b) Webers/m2 c) Weber/m d) Heries Gauss (G) is smaller unit of magnetic induction which is related to tesla (T) as: a) G = 10-1 T b) G = 10-2 T c) G = 10-3 T d) G = 10-4 T A 2m length of a wire is carrying a current of 3 amperes at right angles to uniform magnetic field of 0.4 weber/m2. The force on this length of wire is: a) 2.4 N b) 15 N c) 0.27 N d) 0.6 N The force acting on a charge moving in a magnetic field: a) is proportional to the magnetic of the charge b) is perpendicular to both the magnetic field and the direction of motion c) vanishes when the motion is directly opposite to the direction of the field d) All of the above 1 weber/m2 is equal to: a) One gauss b) 3  1010 gauss 4 c) 10 gauss d) 1/3  10-8 gauss The relative permeability of a material is measured in units of: a) Weber-amp/m b) Weber / amp-m c) Weber/m2 d) Weber  If permeability of material is and its relative permeability is designated  r then:

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Two parallel wires carry current in opposite direction: a) They repel each other b) They attract each other c) They do not effect on another d) Their individual magnetic field cancel each other out The phenomena by which a changing current in one circuit causes an induced emf in another is called: a) The Henry effect b) Self-induction c) Mutual induction d) The magnetic effect The field around a moving charge is called: a) Gravitational field b) Magnetic field c) Conservative field d) None of the above The magnetic effect near the current carrying conductor was discovered by: a) Ampere b) Bohr c) Faraday d) Hans Oersted The most suitable material making permanent magnet is: a) Soft iron b) Steel c) Aluminum d) Cobalt The magnetic field at a point due to a current carrying conductor is directly proportional to: a) Thickness of the conductor b) Resistance of the conductor c) Current passing through the conductor d) Distance from the conductor Two lines of magnetic force: a) Can cross each other b) Always cross each other c) Can never cross each other d) None of the above

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a)  r =  /  c)  r =  

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b)  =  r  d)  =  &  r

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A charged particle moving in a magnetic field experiences a magnetic force given by: a) Fm = qV  B b) Fm = qV. B c) Fm = V  B/q d) Fm = V. B/q A charged particle moving in a magnetic field experiences a resultant force: a) In the direction of the field b) In the opposite direction of the field c) In the direction perpendicular to both the field and its motion d) In the direction opposite to its motion The magnetic force experienced by a charged particle moving in a magnetic field will be maximum if it moves: a) At an angle of 60o to the field b) Parallel to the field c) Anti parallel to the field d) Perpendicular to the field Force on a charged particle having charge ‘q’ moving with velocity V parallel to magnetic field of intensity B is given as: a) F = qVB b) F = qV/B c) F = VB/q d) F = 0 The magnetic force acting on a unit positive charge moving perpendicular to the magnetic field with a unit velocity is called: a) Magnetic flux b) Magnetic filed intensity c) Magnetic induction d) Self inductance The SI unit of magnetic induction is: a) Weber b) Tesla c) Weber per meter d) Gauss A current carrying conductor is placed in a uniform magnetic field parallel to it. The magnetic force experienced by the conductor is: a) F = I/B b) F = I/B sin  c) F = 0 d) F = I/B cos  The SI unit of magnetic induction is tesla which is also equal to: a) Newton / ampere-meter or N/A-m b) Newton / ampere-meter2 or N/A-m2 2 2 c) Newton / ampere -meter or N/A -m d) None of these The relationship between tesla (T) and smaller unit Gauss (G) of magnetic induction is given by: a) 1T = 103 G b) 1T = 10-4 G -2 c) 1T = 10 G d) 1T = 104 G A 5 meter wire carrying a current of 2A is at right angles to the uniform magnetic field of 0.5 weber/m2. The force on the wire is: a) 2N b) 4N c) 5N d) 1.5N Total number of lines of magnetic induction passing through any surface placed perpendicular to the field is called: a) Flux density b) Magnetic induction c) Magnetic flux d) Self inductance Magnetic flux in terms of B and area A normal to B is defined as: a)  = B/A b)  = A/B c)  = BA The SI unit of magnetic flux is: a) NmA-1 c) NmA-2 The unit of magnetic flux is: a) Weber c) Weber-m3 Weber is the unit of: a) Magnetic field intensity c) Magnetic flux The SI unit of flux density is: a) Newton / Amp-m c) Newton-m / Amp The unit of flux density is also given by: a) Weber/m c) Weber

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d)  = B2A

A b) NAm-1 d) Nm2A-1 A b) Weber-m2 d) Henry C b) Magnetic induction d) Magnetic flux density A b) Newton-Amp/m d) Newton-m / Amp2 B b) Weber/m2 d) Weber-m

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The SI unit of flux density (or magnetic induction) is: a) Weber b) Tesla c) Weber per meter d) Gauss The standard vector symbol for flux density is: a)  r b)  o

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c) H d) B When an ion (or charged particle) is projected along a perpendicular path to a uniform magnetic D field, its trajectory is: a) Ellipse b) Helix c) Cycloid d) Circle An electron enters a region where the electric field E is perpendicular to the magnetic field B. It will C suffer no deflection if: a) E = Be  b) B = eE/   c) E = B d) E = Be  / 2 Magnetic field along the axis of a solenoid with n turns per meter carrying a current I is given by: C   a) B = o NI b) B = o /NI c) B =  o nI

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d) B =  o I/n

The equation B =  o NI/2  R for a toroid can be derived by applying: a) Ohm’s law b) Lenz’s law c) Ampere’s law d) Faraday’s law Which one of the following particles moving in the magnetic field cannot be deflected? a)  -particle b)  -particle c) Electron d) Neutron The experiments show that whenever there is a change in the magnetic flux linked with a loop or closed circuit there is always: a) Inductance induced b) An emf induced c) A charge induced d) Capacitance induced Electromagnetic induction is the phenomenon in which an emf is induced in the coil (or circuit) due to the change of flux through it when: a) The coil is moved in magnetic field b) The coil is placed in magnetic field c) The coil is moved in electric field d) The coil is placed in electric field Lenz’s law is in accordance with the law of conservation of: a) Momentum b) Angular momentum c) Charge d) Energy The process in which a change of current in one coil causes an induced emf in another coil nearby it is called: a) Self induction b) Mutual induction c) Self inductance d) The Henry effect The mutual inductance of coils depends upon: a) Stiffness of the coils b) Density of the coils c) Material of the coils d) None of above Mutual inductance has a practical role in the performance of the: a) Radio choke b) A.C. Generator c) D.C. Generator d) Transformer The phenomenon of producing emf in the coil due to change of current in the coil itself is called: a) Mutual induction b) Self induction c) Self flux change d) Mutual inductance The SI unit of self inductance or mutual inductance is: a) Maxwell b) Weber c) Henry d) Tesla Inductance is measured in: a) Ohm b) Volt c) Henry d) Weber A 50mh coil carries a current of 2 amp. The energy stored in its magnetic field is: a) 0.05 Joule b) 0.1 Joule c) 10 Joule d) 100 Joule

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The motional emf developed in a conductor depends upon: a) Length b) Orientation c) Magnetic field d) All of these A generator is a device which converts: a) Mechanical energy into electrical energy b) Chemical energy into mechanical energy c) Kinetic energy into potential energy d) Electrical energy into mechanical energy The emf is induced in a coil of a A.C. generator under the phenomenon of: a) Electrostatic induction b) Self-induction c) Mutual induction d) Electromagnetic induction In case of alternating current, the average value of current and voltage is: a) Less than zero b) Greater than zero c) Zero d) 1 An A.C. voltage measures Vo volts in a circuit. Its peak value is given by: a) Vo

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b) Vo /

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2 / Vo 2 Vo c) d) An alternating current is converted into direct current by a: a) Motor b) Rectifier c) Dynamo d) Transformer A.C. can be measured with the help of: a) Heating effect b) Magnetic effect c) Chemical effect d) The Henry effect Which of the following converts electrical energy into mechanical energy? a) Transformer b) Motor c) D.C. Generator d) A.C. Generator An electric motor is a device which converts: a) Mechanical energy into electrical energy b) Heat energy into mechanical energy c) Magnetic energy into mechanical energy d) Electrical energy into mechanical energy For electroplating we use: a) A D.C. source b) An A.C. source c) Any source d) None of the above The only difference between construction of D.C generator and an A.C. generator is that of: a) Carbon brushes b) Coil c) Commutator d) Magnetic field A.C. and D.C. have the same: a) Affect in charging a capacitor b) Affect in charging a battery c) Affect while passing through an inductance d) Heating effect through a resistance Device used for converting A.C. into D.C. is called: a) An amplifier b) An oscillator c) A voltmeter d) A rectifier A transformer is a device which: a) Only steps down A.C. voltage b) Only steps up S.C. voltage c) Steps up or steps down A.C. voltage d) Steps up D.C. voltage A transformer consists of an iron core with: a) A primary coil b) A secondary coil c) Neither primary nor secondary d) Primary coil and secondary coil A transformer is used to change: a) The voltage of direct current b) The voltage of alternating current c) The electrical energy d) The magnetic field A device consisting of two coils wound or iron core is called a: a) Rectifier b) A.C. Generator c) D.C. Generator d) Transformer The practical application of the phenomenon of mutual induction is: a) Electric motor b) Transformer c) A.C. Generator d) D.C. Generator Frequency of A.C. used in Pakistan is: a) 100 CPs b) 60 CPs c) 50 CPs d) 120 CPs

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A wire loop is moved parallel to a uniform magnetic field. The induced emf in the loop: a) Depends on the shape of the loop b) Depends on the area of the loop c) Depends on the nature of the loop d) Is zero Henry is the unit of: a) Self inductance only b) Mutual inductance only c) Both self-inductance and mutual inductance d) Induced emf The inductance of a coil plays the same role as: a) Angular momentum plays in mechanics b) Momentum plays in mechanics c) Energy plays in mechanics d) Inertia plays in mechanics An alternating current is that which: a) Changes continuously in magnitude and reverse periodically in direction b) Gets only its direction reversed after equal intervals of time c) Varies in magnitude d) Flows intermittently An A.C. voltmeter measures Vo volts in a circuit. Its peak value is: a)

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2 c) Vo d) According to Faraday’s law, the emf induced in a conductor that is moved in magnetic field depends upon: a) Change in magnetic flux b) Rate of change of magnetic flux c) Final magnetic flux d) Initial magnetic flux A transformer is used to: a) Transform alternating current voltage b) Convert direct current into alternating current c) Convert alternating current into direct current d) convert mechanical energy into electrical energy Tick the incorrect statement: a) There is always a lateral repulsion between adjacent lines of force b) The lines of force originate at the north pole and end at the south pole c) A compass needle sets itself perpendicular to the lines of force d) Line of force is an imaginary curve Tick the wrong statement in relation to an electric field: a) The tangent to a line of the force gives the direction of electric field b) The tangent to a line of force also gives the magnitude of the electric field c) The lines of force per unit cross-sectional area of field gives the magnitude of electric field d) The electric field is a conservative field Particles having positive electric charge occasionally come with high velocity from the sky towards the earth. On account of the magnetic field of the earth, they would be deflected towards: a) West b) East c) South d) North Flux density B is related to the magnetic flux N by the relation: N B a) B = A b) N = A c) A = BN d) B2 = AN A charge moves through a magnetic field with a certain velocity. Direction of force can be obtained by applying: a) Cork screw rule b) Rule of cross product of vectors c) Fleming’s right hand rule d) Ampere’s rule  In moving coil galvanometer, the deflection of the coil is related to the electric current by the relation: a) I  tan  b) I   2 c) I   d) I   A compass needle will be deflected if it is kept near a: a) Positively charged body at rest b) Charged body in motion c) Negatively charged body d) None of these

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CHAPTER # 14 Magnetism and Electromagnetism

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Magnetic field is measured by: a) Galvanometer b) Ammeter c) Fluxmeter d) Thermometer Which of the following substance will be most suitable for the transformer core: a) Soft iron b) Nickel c) Copper d) Steel A choke coil is used as a resistance in: a) Wheatstone circuit b) D.C. potentiometer circuit c) D.C. circuit d) A.C. circuit A.C. has replaced D.C. in our homes because: a) A.C. can be transmitted economically b) A.C. is more safe c) Production cost of D.C. is more d) A.C. can be produced easily When a coil is moved in a magnetic field, the induced emf in it depends on: a) Initial magnetic flux b) Final magnetic flux c) Rate of change of magnetic flux d) Change of magnetic flux The ratio of the turns in the primary and secondary coil of transformer is 10, then the ratio of e.m.f. will be: a) 10 : 5 b) 20 : 1 c) 10 : 1 d) 1 : 1 A current is flowing north along a power line. The direction of the magnetic filed above it, neglecting the earth’s field, is: a) West b) South c) East d) North The magnitude of e.m.f. across the secondary coil of a transformer does not depend upon: a) The magnitude of the e.m.f. applied across the primary coil b) The number of turns in the primary coil c) The number of turns in the secondary coil d) the resistance of the primary and secondary coils Magnetic fields do not interact with: a) Moving permanent magnets b) Stationary permanent magnets c) Moving electric charges d) Stationary electric charges The needle of a magnetic compass: a) Aligns itself perpendicular to a magnetic field b) Aligns itself parallel to a magnetic field c) Rotates in the magnetic field of an electric currentd) Is affected only by permanent magnets Tick the correct relation: a) 1T = 103G b) 1T = 104G 2 c) 1T = 10 G d) 1T = 10-2G Tick the wrong statement: a) The charge moving parallel to B with a certain velocity V experiences no force b) The charge moving with velocity V perpendicular to B experiences maximum force c) The force is always perpendicular to V and B d) The force is inversely proportional to q and V Electromotive force is most closely related to: a) Inductance b) Potential difference c) Magnetic flux density d) Electric field intensity The e.m.f. produced in a wire by its motion across a magnetic field does not depend upon: a) The orientation of the wire b) the composition of the wire c) The diameter of the wire d) The length of the wire A charged particle moves through a magnetic field. The effect of the field is to change the particle’s: a) Energy b) Velocity c) Speed d) Direction of motion The time required for a charged particle to make a complete revolution in a magnetic field does not depend upon: a) The magnetic flux density b) Its energy c) Its charge d) Its mass The radius of curvature of the path of a charged particle in a uniform magnetic field is directly proportional to: a) The flux density of the field b) The particles energy c) The particle’s momentum d) The particle’s charge

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The fact that an electric field is produced in a conductor whenever magnetic lines of force move across it is referred to as: a) Lenz’s law b) Faraday’s law c) Ohm’s law d) Ampere’s law The unit of magnetic induction is: a) weber.m2 b) weber / amp c) weber / m2 d) weber Transformers are not used in: a) A.C. circuits b) D.C. circuits c) Integrated circuits d) Both A.C. and D.C. circuits The direction of an induced current is such that it opposes the cause that produces it, is the statement of: a) Faraday’s law b) Lenz’s law c) Ampere’s law d) Gauss’s law The relation between Tesla and Gauss is: a) 1 T = 10 G b) 1 T = 102 G 3 c) 1 T = 10 G d) 1 T = 104 G The effective value of an alternating current is: a) 3 times its maximum value b) 2 times its maximum value 1 1 3 times its maximum value 2 its maximum value c) d) Tesla is equal to: a) N/Am b) N/Am2 2 2 c) N/A m d) N/A2m When a charged particle is projected perpendicularly to a uniform magnetic field its trajectory is: a) Straight line b) Elliptical c) Cycloid d) Circular The induced current is obtained by moving a loop of wire: a) Across a magnetic field b) Across an electric field c) Across a gravitational field d) In field free space The SI unit of magnetic induction is: a) Webber b) Webber per meter c) Henry d) Tesla Magnetic flux passing normally through a unit area is called: a) Flux density b) Magnetic filed intensity c) Magnetic field lines d) Magnetization The change of magnetic flux through a circuit will produce: a) Magnetic field b) Electric field c) Induced emf d) Alternating current A device used for converting AC into DC is: a) Amplifier b) Rectifier c) Oscillator d) Generator In Pakistan, the voltage stepped down for domestic use is: a) 260 volts b) 220 volts c) 200 volts d) 180 volts The magnetic flux through the area A is: a) A  B b) B . A c) B  A d) B / A When a wire of length 3 cm is moved with a velocity of 2m/s perpendicularly in a magnetic field of strength 10 tesla then the e.m.f. induced is: a) 0.2 V b) 0.4 V c) 0.6 V d) 0.8 V A 15 cm wire, moving with a velocity 2 m/sec acquires an induced e.m.f. of 0.003 V whenever dragged in a magnetic field of strength: a) 0.01 tesla b) 0.02 tesla c) 0.03 tesla d) 0.04 tesla

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CHAPTER # 14 Magnetism and Electromagnetism

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Which one of the following is magnitude of force acting on 1 m long wire carrying current 2A and held perpendicular to the magnetic field of 1 / 2 tesla? a) 1 N b) 1 / 2 N c) 1 / 3 N d) 1 / 4 N The phenomenon in which a change of current in one coil produces an induced emf in another coil nearby is called: a) Self inductance b) Self induction c) Mutual induction d) Mutual inductance A force of 5 N is acting on a wire of length 1 m, held perpendicular in a uniform magnetic field of strength 5 web/m2 then the value of current passing through it will be: a) 5 A b) 3 A c) 1 A d) 2 A The particle which cannot be deflected in a magnetic field is: a)  -particle b)  -particle c) Electron d) Neutron A particle of charge ‘q’ and mass ‘m’ moving with a velocity ‘v’ enters perpendicularly in a uniform magnetic field ‘B’ describes a circular path. What will be the radius of that path? a) mv / Bq b) mqv / B c) mvB / q d) mqB / v 240 KW electric power is sent to an area 20 km away from the power plant. If the transformer lines have total resistance of 5 Ohm, then 24  103 volts, the power loss will be: a) 200 watts b) 300 watts c) 400 watts d) 500 watts If a certain transformer having 200 turns in its primary coil converts 11000 voltage to 220 volts for domestic purpose then the number of turns in secondary coil should be: a) 3 b) 4 c) 5 d) 6 Transformer is used to: a) Increase alternating voltage only b) Decrease alternating voltage c) Increase or decrease alternating voltage d) Increase or decrease direct current voltage In step-up transformer: a) Ns > Np b) Ns < Np c) Ns = Np d) Ns = 0

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