Chapter 20 Induced Voltages and Inductance CHAPTER 20 Conceptual Questions C1 A double loop of wire making 2 turns is in the x y plane centered at the origin A uniform magnetic field is increasing at a constant rate in the positive z direction Viewed from the positive z axis in which direction is the induced magnetic field in the loop a in the positive z direction b in the negative z direction c There is no induced field because of the double loop d There is no induced field because the rate of change of the magnetic field is constant C2 A circular loop of wire has its radius reduced in half in time t A uniform magnetic field is at an angle of 60 to the plane of the coil and the magnetic field doubles its intensity in the same time interval t During this interval what happens to the flux through the coil a It increases b It decreases c It remains the same d More information is needed to make this conclusion C3 Two solenoids wound from wire from the same spool have the same length and crosssectional area but solenoid 1 has half the turns of solenoid 2 If these solenoids are each connected to a circuit and the only non negligible resistance is that of the solenoids which solenoid gives the greater time constant and by what factor a 1 by a factor of 2 b 2 by a factor of 2 c 2 by a factor of 4 d No answer above is completely correct C4 One time constant after an RL circuit has its switch closed how does the current I in it compare to the maximum current Imax that occurs for this circuit a I Imax 2 b I Imax 2 c I Imax 2 d Without knowing R and L this cannot be determined C5 Three loops of wire one circular one rectangular and one square are made from identical lengths of wire If the loops are in the same increasing magnetic field perpendicular to the plane of the coils which loop has the greatest induced emf a the circular one 86 Chapter 20 Induced Voltages and Inductance b the rectangular one c the square one d All three would have the same emf induced 87 Chapter 20 Induced Voltages and Inductance 20 1 Induced emf and Magnetic Flux 1 A uniform 4 5 T magnetic field passes perpendicularly through the plane of a wire loop 0 10 m2 in area What flux passes through the loop a 5 0 T m2 b 0 45 T m2 c 0 25 T m2 d 0 135 T m2 2 A uniform 4 5 T magnetic field passes through the plane of a wire loop 0 10 m 2 in area What flux passes through the loop when the direction of the 4 5 T field is at a 30 angle to the normal of the loop plane a 5 0 T m2 b 0 52 T m2 c 0 39 T m2 d 0 225 T m2 3 A loop of area 0 250 m2 is in a uniform 0 020 0 T magnetic field If the flux through the loop is 3 83 10 3 T m2 what angle does the normal to the plane of the loop make with the direction of the magnetic field a 40 0 b 50 0 c 37 5 d This is not possible 4 A coil in a magnetic field encloses a flux of 0 256 T m 2 when the angle between the normal to the coil and the direction of the magnetic field is 70 0 What flux would go through the coil if the angle were changed to 40 0 a 0 332 T m2 b 0 198 T m2 c 0 114 T m2 d 0 573 T m2 5 A coil is placed in a magnetic field and has a flux B through it The coil is stressed so that its area reduces to 75 of its original value If the plane of the coil stays the same and the flux through it remains the same how must the magnetic field change a It must increase by 25 b It must increase by 33 88 Chapter 20 Induced Voltages and Inductance c It must increase by 125 d It must decrease by 25 89 Chapter 20 Induced Voltages and Inductance 20 2 Faraday s Law of Induction 6 The units T m2 s are equivalent to a W b V c N m d webers 7 A sensitive ammeter is connected to a wire loop and placed within the magnetic field of a strong horseshoe magnet The ammeter shows a deflection when a the wire is moved parallel to the field b the wire is moved perpendicularly to the field c neither wire nor magnet is moving d the wire s axis is parallel to the field 8 According to Lenz s law the direction of an induced current in a conductor will be that which tends to produce which of the following effects a enhance the effect which produces it b produce a greater heating effect c produce the greatest voltage d oppose the effect which produces it 9 GFI stands for a grand flux indicator b ground forcing indicator c ground fault interrupter d gauss free invention 10 The principle or law that says an induced emf in a circuit loop produces a current whose magnetic field opposes further change of magnetic flux is credited to a Faraday b Lenz c Ampere d Volta 11 A square coil enclosing an area with sides 2 0 cm long is wrapped with 2 500 turns of wire A uniform magnetic field perpendicular to its plane is turned on and increases to 0 25 T during an interval of 1 0 s What average voltage is induced in the coil 90 Chapter 20 Induced Voltages and Inductance a 0 25 V b 0 12 V c 2 0 V d 2 5 V 12 A 10 turn square coil of area 0 036 m2 and a 20 turn circular coil are both placed perpendicular to the same changing magnetic field The voltage induced in each of the coils is the same What is the area of the circular coil a 0 072 m2 b 0 60 m2 c 0 018 m2 d 0 036 m2 13 A bar magnet is falling through a loop of wire with constant velocity The south pole enters first As the magnet leaves the wire the induced current as viewed from above a is clockwise b is counterclockwise c is zero d is along the length of the magnet 14 A flat coil of wire consisting of 20 turns each with an area of 50 cm 2 is positioned perpendicularly to a uniform magnetic field that increases its magnitude at a constant rate from 2 0 T to 6 0 T in 2 0 s If the coil has a total resistance of 0 40 what is the magnitude of the induced current a 70 mA b 140 mA c 500 mA d 800 …