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Class 2 Today we will: • learn the basic characteristics of the electrostatic force • review the properties of conductors and insulators • learn what is meant by “electrostatic induction” • find out why static electrostatic forces are usually attractive • discuss the problem of force at a distance • learn the basics of two types of models that explain why there are forces Clicker Question 1 When babies are rubbed, they gain a net charge. Does the ceiling need a net charge for the babies to stick to it? A. yes B. no Clicker Question 2 If the ceiling has no net charge, is it possible for the babies to be repelled by the ceiling? A. yes B. no Clicker Question 3 If the virtual particles were uncharged real particles, the force would be A. always attractive. B. always repulsive. C. either attractive or repulsive. D. There would be no force. Answers 1B 2B 3B Class 3 Today we will: • learn how the thread model describes the force between point charges at rest • construct Coulomb’s law from the thread model • learn how to use Coulomb’s law to calculate the force between charges at rest Clicker Question 1 source charge field charge Force The field particle is A. positive B. negative C. neutral D. You can’t tell. Clicker Question 2 qs q f r F 40 r 3 +3C (2, 3) −4C (7, 1) If we wish to find the force on the blue particle, A. the blue particle is the source particle. B. the blue particle is the field particle. C. both particles are source particles. D. both particles are field particles. E. none of the above. Clicker Question 3 qs q f r F 40 r 3 +3C (2, 3) −4C (7, 1) The vector r goes from the source particle to the field particle. A. r 7 xˆ 1 yˆ B. r 2 xˆ 3 yˆ C. r 5 xˆ 2 yˆ D. r 5 xˆ 2 yˆ E. r 5.39 Answers 1A 2B 3D Class 4 Today we will: • review the meaning of potential energy • find the potential energy of point charges at rest • learn a few basic ideas about relativity • find out how relativity affects the threads emitted by a moving source Clicker Question 1 In a region of space, the force on a positive test charge is zero. In this region, the potential energy is A. positive. B. negative. C. zero. D. a constant, but not necessarily zero. F 0 Clicker Question 2 v c The SI units for β are: A. m/s2 B. m2/s C. m2/s2 D. β is dimensionless Clicker Question 3 rest moving H 0 L H' L' A. L L and 0 B. H H and 0 C. L L and 0 D. H H and 0 E. L L and 0 Answers 1D 2D 3E Class 5 Today we will: • learn the meaning of head lines, tail lines, and ray lines. • find a force equation for a moving source charge (like Coulomb’s law, but for a source with constant velocity). • learn how stubs can be used to make a account for the motion of field particles. Clicker Question 1 P B D E - out of screen C S A U A source charge and a field charge are both positive. The source at S emits threads that arrive at P when the source has moved to U. What is the direction of the thread? Clicker Question 2 P B D E - out of screen C S A U A source charge and a field charge are both positive. The source at S emits threads that arrive at P when the source has moved to U. What is the direction of the thread (electric) force? Clicker Question 3 P B D E - out of screen C S A U A source charge and a field charge are both positive. The source at S emits threads that arrive at P when the source has moved to U. What is the direction of the head line? Clicker Question 4 P B D E - out of screen C S A U A source charge and a field charge are both positive. The source at S emits threads that arrive at P when the source has moved to U. What is the direction of the stub? Clicker Question 5 B A P v E - out of screen C D S U A source charge and a field charge are both positive. The source at S emits threads that arrive at P when the source has moved to U. What is the direction of the stub (magnetic) force? Answers 1B 2B 3D 4E 5D Class 6 Today we will: • learn that threads and stubs can be aligned to form electric and magnetic field lines. • derive the Lorentz force law. • integrate to find the electric and magnetic fields of a proton beam. Clicker Question 1 P B D E - out of screen C S A U A source charge and a field charge are both positive. The source at S emits threads that arrive at P when the source has moved to U. What is the direction of the stubs? Clicker Question 2 A proton travels vertically downward through a region where there is an electric field pointing to the east. What is the direction of the force? A. downward B. to the east C. to the south D. to the north E. to the west Clicker Question 3 A proton travels vertically downward through a region where there is a magnetic field pointing to the east. What is the direction of the force? A. downward B. to the east C. to the south D. to the north E. to the west Clicker Question 4 An electron travels vertically downward through a region where there is a magnetic field pointing to the east. What is the direction of the force? A. downward B. to the east C. to the south D. to the north E. to the west Answers 1E 2B 3C 4D Class 7 Today we will: • learn how to do problems using the Lorentz force law. • learn the meaning of the electric potential and how it relates to the potential energy. • learn three ways of representing fields geometrically. Clicker Question 1 v 5.00 m/s xˆ. B 3.50 mT xˆ 2.00 mT yˆ. If we change the magnetic field to B 7.00 mT xˆ 2.00 mT yˆ. what happens to the force? Before: A. B. C. D. E. It doubles. Its get smaller by a factor of 2. Its z-component doubles. Its z-component gets smaller by factor of 2. Nothing changes. Clicker Question 2 An electron passes through a 1.0 V battery. The electron charge is e 1.602 1019 C. By how much does the energy of the electron increase? A. U 1.602 10 19 J. B. U 3.204 10 19 J. C. U 0.80110 19 J. D. U 0 J. Clicker Question 2 An electron passes through a 1.0 V battery. The electron charge is e 1.602 1019 C. Batteries increase the potential energy of electrons by pushing them closer together. Clicker Question 3 Two identical spheres have charges +q. They are separated by a distance d. At the midpoint between the spheres, the magnitude of the electric field is: 1 8q A. E 40 d 2 1 2q C. E 40 d 2 1 4q B. E 40 d 2 1 q D. E 40 d 2 E. E 0 +q +q Clicker Question 4 Two identical spheres have charges +q. They are separated by a distance d. At the midpoint between the spheres, the electric potential is: 1 4q A. V 40 d 1 q C. V 40 d 1 2q B. V 40 d 1 q D. V 40 2d E. V 0 +q +q Answers 1E 2A 3E 4A Class 8 Today we will: • learn about static electric fields and electric potentials in conductors. • learn how charges move in regions where there are electric and magnetic fields. • learn about some practical devices that use electric and magnetic fields. Clicker Question 1 A net charge of +1.0 mC is placed on a steel ball. The ball is then placed in the electric field of a Van de Graaff generator. The total charge on the surface of the steel ball is: A. zero B. + 0.5 mC C. – 0.5 mC D. + 1.0 mC E. – 1.0 mC Clicker Question 2 After a positive charge is “shot” into a region where there is a uniform magnetic field, it spirals clockwise out of the screen. If a negative charge were shot into this region, it would: A. spiral clockwise out of the screen B. spiral clockwise into the screen C. spiral counterclockwise out of the screen D. spiral counterclockwise into the screen Answers 1D 2C Class 9 Today we will: • learn about current, voltage, and power in circuits. • learn about resistance of materials and how resistance depends on geometry and temperature. • introduce Ohm’s law. Clicker Question 1 What current passes through a 60 W light bulb? (Line voltage is 120 V.) A. 0.5 A B. 1.0 A C. 2.0 A D. 7200 A E. All of the above Clicker Question 2 One block has resistance R. What is the resistance when two blocks are joined at the midpoints as shown: A.R/2 B.R C.3R/2 D.5R/4 E.2R Clicker Question 2 One block has resistance R. What is the resistance when two blocks are joined at the midpoints as shown: A.R/2 B.R C.3R/2 D.5R/4 E.2R Hint: Divide the combination into three regions. Answers 1A 2D Class 10 Today we will: • learn how to determine if two resistors are in series or parallel. • find out how resistors combine when connected in series and parallel. • work examples of series-parallel reduction to find current, voltage and power in resistance networks. Clicker Questions 1-6 Series-Parallel Quiz Answer the following six questions to see if you understand what series and parallel mean. 1. Resistors A and B are in 1. series 2. parallel 3. neither 2. Resistors A and B are in 1. series 2. parallel 3. neither 3. Resistors A and B are in 1. series 2. parallel 3. neither 4. Resistors A and B are in 1. series 2. parallel 3. neither 5. Resistors A and B are in 1. series 2. parallel 3. neither 6. Resistors A and B are in 1. series 2. parallel 3. neither Quiz Answers 1. series 2. neither 3. neither 4. parallel 5. series 6. parallel Class 11 Today we will: • discuss Kirchoff’s loop and node equations. • learn how to determine the number of loop and the number of node equations we will need. • write Kirchoff’s equations for a sample circuit. Clicker Question 1 A. I1 I 2 I 3 The junction equation for junction A is: B. I 3 I1 I 6 C. I 3 I 6 I1 A I1 D. I 3 I1 I 6 I3 E. I1 I 6 I 3 0 B I6 D I4 I5 I2 C Clicker Question 2 The loop equation for loop 2 is: A I1 A. I 6 I 3 6 I 5 I 6 0 + B. 3I 6 2 I 3 6 6 I 5 7 I 6 0 I3 ++ 1 C. 3I 6 2 I 3 6 6 I 5 7 I 6 0 B D. 3I 6 2 I 3 6 6 I 5 7 I 6 0 + + E. 3I 6 2 I 5 6 I 5 6 I 5 7 I 6 I04 I2 + 2 D 3 + C I5 + I6 Answers 1C 2D Class 12 Today we will: • discuss test policies. • review Lessons 1 – 4 to prepare for the exam. Clicker Question 1 Your answer is 0.00467. What is the first significant digit? A: 0 B: 4 C: 5 Clicker Question 2 Your answer is 1.38×103. What is the exponent? A: 1 B: 2 C: 3 D: 4 Answers 1B 2C Class 13 Today, we will: • review characteristics of field lines and contours • learn more about electric field lines and contours of point charges • learn more about magnetic fields and contours of long, straight wires Clicker Question 1 The strength of a field is given in terms of field lines by: A. the number of lines per unit length. B. the number of contours per unit length. C. the number of lines per unit area. D.the number of contours per unit area. Clicker Question 2 The wire law for magnetic fields is represented geometrically by A. the magnetic field lines. B. the magnetic field contours. C. the electric field lines. D.the electric field contours. Answers 1C 2B Class 14 Today, we will: • learn how to draw the total electric field of two point charges. • find that the electric field is like a single point in the near field and the far field. • use symmetry to find the electric field lines of charged spheres, cylinders, and planes. Clicker Question 1 Is this picture OK? A – yes B -- no +1 –1 Clicker Question 1 Is this picture OK? A – yes B -- no +1 –1 •Field lines can not cross. •The near field is incorrect. Clicker Question 2 Is this picture OK? A – yes B -- no +2 –1 Clicker Question 2 Is this picture OK? A – yes B -- no +2 –1 •The far field is incorrect. •The near field isn’t drawn well. Answers 1B 2B Class 15 Today, we will: • learn to visualize magnetic field lines for two wires. • learn to visualize electric and magnetic field contours for two charges or wires. Clicker Question 1 In three dimensions, the closed, blue lines are deformed: A. loops B. spheres C. cylinders D. disks Clicker Question 2 In three dimensions, the elements of the field contour are sections of: A. loops B. spheres C. cylinders D. disks Answers 1B 2C Class 16 Today, we will: • learn what a capacitor is. • learn the definition of capacitance. • find the electric field and voltage inside a parallel-plate capacitor. • find the capacitance of the capacitor. • learn that a dielectric is a material with polar molecules. • learn how dielectrics increase capacitance. • find the energy stored in a capacitor and in the electric field. Clicker Question 1 A 4μF capacitor with a plate separation d is charged by connecting it to a 6 V battery. The battery is disconnected and the plates separated to 2d. The new capacitance and voltage are: A. B. C. D. E. 8 μF and 12 V. 8 μF and 3 V. 2 μF and 12 V. 2 μF and 3 V. Nothing changes. Q E 0 A C 0 A d Clicker Question 2 When compared to a capacitor with no dielectric, adding a dielectric A. always increases capacitance. B. sometimes increases capacitance. C. never increases capacitance. Answers 1C 2A Class 17 Today, we will: • learn how to combine capacitors in series and parallel • find that circuits RC circuits have charges and currents that depend on exponential functions • learn the meaning of the exponential time constant • find that the exponential time constant for an RC circuit is τ=RC Clicker Question 1 A. 1F What is the equivalent capacitance of these three capacitors? B. 3F C . 6 F D. 9 F E . 12 F 3F 3F 3F 3F 3F 3F Clicker Question 2 What is the equivalent capacitance of these three capacitors? A. 1F B. 3F C . 6 F D. 9 F E . 12 F Clicker Question 3 What is the time constant of the green (middle) curve? A. 1 s B. 2 s C. 3s D. 4s E. 5 s 1 e Answers 1A 2D 3C Class 18 Today, we will: • learn the definition of a Gaussian surface • learn how to count the net number of field lines passing into a Gaussian surface • learn Gauss’s Law of Electricity • learn Gauss’s Law of Magnetism Clicker Question 1 What is the net number of field lines passing through the Gaussian surface? A. -8 B. -4 C. 0 D. +4 E. +8 Clicker Question 2 What is the net number of field lines passing through the Gaussian surface? A. -8 B. -4 C. 0 D. +4 E. +8 Clicker Question 3 What is the net number of field lines passing through the Gaussian surface? A. -8 B. -4 C. 0 D. +4 E. +8 Clicker Question 4 What is the net number of field lines passing through the Gaussian surface? A. -8 B. -4 C. 0 D. +4 E. +8 Clicker Question 5 What is the net number of field lines passing through the Gaussian surface? A. -8 B. -4 C. 0 D. +4 E. +8 Clicker Question 6 What is the net number of field lines passing through the Gaussian surface? A. -8 B. -4 C. 0 D. +4 E. +8 Answers 1E 2E 3A 4A 5C 6C Class 19 Today, we will: • learn how to use Gauss’s law and symmetry to find the electric field inside a shperical charge distribution • show that all the static charge on a conductor must reside on its outside surface • learn that why cars are safe in lightning but cows aren’t Clicker Question 1 The magnitude of the electric field E(r) outside a uniformly charged sphere (that means ρ is a constant) of radius a is best represented by which of the following graphs? E(r) E(r) A. B. a r E(r) E(r) C. D. a r a r a r Clicker Question 2 The magnitude of the electric field E(r) inside a uniformly charged sphere of radius a is best represented by which of the following graphs? E(r) E(r) A. B. a r E(r) E(r) C. D. a r a r a r Answers 1B 2A Class 20 Today, we will: • learn how integrate over linear, surface, and volume charge densities to find the total charge on an object • learn that flux is the mathematical quantity that tells us how many field lines pass through a surface Clicker Question 1 A cylinder of length L and radius R has a charge density z where is a constant and z is the distance from one end. Find the total charge on the cylinder. 4 How do you slice the cylinder? A. into cylindrical shells B. into discs C. into wedges D. into rectangles E. into rectangular prisms Clicker Question 2 A cylinder of length L and radius R has a charge density z where is a constant and z is the distance from one end. Find the total charge on the cylinder. 4 What is the volume of each slice? A. dV 2rdz B. dV 2Rdz C. dV 2rLdr D. dV r dz 2 E. dV R dz 2 Clicker Question 3 A cylinder of length L and radius R has a charge density z where is a constant and z is the distance from one end. Find the total charge on the cylinder. 4 What are the limits of integration? A. 0 to z B. -z to +z C. 0 to L D. -L to +L E. 0 to r Clicker Question 4 A sphere of radius R has a charge density r where is a constant. Find the total charge on the sphere. How do you slice the sphere? A. into discs, sliced in the x-direction. B. into discs, sliced in the y-direction. C. into discs, sliced in the z-direction. D. into spherical shells. E. into wedges. Clicker Question 5 A sphere of radius R has a charge density r where is a constant. Find the total charge on the sphere. What is the volume of each slice? A. dV 2rdr B. dV 4R 2 dr C. dV 4r 2 dr D. dV r 2 dz 4 3 E. dV r dr 3 Clicker Question 6 A sphere of radius R has a charge density r where is a constant. Find the total charge on the sphere. What are the limits of integration? A. 0 to R B. 0 to r C. –R to +R D. –r to +r E. all of the above Answers 1B 2E 3C 4D 5C 6A Class 21 Today, we will: • learn how to use Gauss’s law to find the electric fields in cases of high symmetry • insdide and outside spheres • inside and outside cylinders • outside planes Clicker Question 1 Gauss’s law states: EA qenc 0 The Gaussian surface we choose: A. B. C. D. can be any surface can be any closed surface can be only an element of a field contour can be only an element of a field contour where the magnitude of the E field is the same everywhere on the surface. Clicker Question 2 Gauss’s law states: EA qenc 0 In this equation, A represents: A. the surface area of the charged object. B. the surface area of the Gaussian surface. C. the surface area of Mars. Clicker Question 3 Gauss’s law states: EA qenc 0 In this equation, qenc always represents: A. the total charge of the object. B. only the charge enclosed within the Gaussian surface. C. the charge of an electron. D. the charge off an electron. Answers 1D 2E 3C Class 22 Today, we will: • learn the meaning of an Amperian loop • learn how to count the number of perpendicular surfaces pierced by a line • learn Ampère’s law: the net number of perpendicular surfaces pierced by an Amperian loop is proportional to the current passing through the loop • find how Ampère’s law and symmetry show that the magnetic field inside a hollow wire is zero • learn that the number of pierced surfaces is mathematically represented by the line integral. Clicker Question 1 What is the net number of surfaces pierced by this Amperian loop? A. -16 B. -8 C. 0 D. +8 E. +16 Clicker Question 2 What is the net number of surfaces pierced by this Amperian loop? A. -16 B. -8 C. 0 D. +8 E. +16 Answers 1E 2C Class 23 Today, we will use Ampere’s law to find the magnetic fields • inside and outside a long, straight wire with radial charge density • of a plane of wires • of a solenoid • of a torus Clicker Question 1 A wire of radius R has current density j r.2 Find the magnetic field inside the wire. What is the correct expression for the ℓ in the line integral? A. r 2 B. R C. 2 r D. 2 R 2 E. None of the above. Clicker Question 2 A wire of radius R has current density j r.2 Find the magnetic field inside the wire. What is the correct expression for ienc ? r A. ienc r 2 rdr 2 R B. ienc r 2 rdr 0 0 r R C. ienc r 4 r dr 2 2 2 D. ienc r 4 r dr 0 0 E. None of the above. 2 2 Clicker Question 3 A wire of radius R has current density j r 2. Find the magnetic field inside the wire. A. B(r ) 0 r 3 4 3 r C. B(r ) 0 3 B. B(r ) 0 R 4 4r 3 R D. B(r ) 0 3 E. None of the above. Clicker Question 4 A wire of radius R has current density j r 2. Find the magnetic field outside the wire. A. B(r ) 0 r 3 4 3 r C. B(r ) 0 3 B. B(r ) 0 R 4 4r 3 R D. B(r ) 0 3 E. None of the above. Answers 1C 2A 3A 4B Class 24 Today, we will use direct integration to find • electric fields of charged rods and loops • electric potentials of charged rods and loops • magnetic fields of current-carrying wire segments and loop segments (Biot-Savart law) Clicker Question 1 Are you here? A.Yes B. No Clicker Question 2 Are you still here? A.Yes B. No Answers 1A 2A Class 25 Today, we will: • learn the definition of divergence in terms of flux. • learn the definition of curl in terms of the line integral. • • find the gradient, divergence, and curl in terms of derivatives (differential operators) • write Gauss’s laws and Ampere’s law in differential form • work several sample problems Clicker Problem 1 You know both the electric and magnetic fields in a region of space. If you wish to find the volume charge density, you could use the differential form of A. Gauss’s law of electricity B. Gauss’s law of magnetism C. Ampere’s law D. Faraday’s law E. Coulomb’s law Clicker Problem 2 12xy j ( x, y ) zˆ 0 Which picture best describes the current? Take red to be out of the screen and blue to be into the screen. y y x A y x B y x C x D Answers 1A 2B Class 27 Today we will: • learn the definitions of electric and magnetic dipoles. •find the forces, torques, and energies on dipoles in uniform fields. •learn what happens when we put dipoles in nonuniform fields. Clicker Question 1 At what angle θ is the torque on the dipole maximum? A. 0° B. 45° C. 90° D. 135° E. 180° B A Clicker Question 2 At what angle θ is the potential energy of the dipole maximum? A. 0° B. 45° C. 90° D. 135° E. 180° B A Answers 1C 2E Class 28 Today we will: • define magnetization and magnetic susceptiblity • learn about paramagnetic, diamagnetic, and ferromagnetic materials • learn about the opposing effects of domain alignment and thermal disalignment • learn how to understand hysteresis curves • characterize ferromagnetic materials in terms of residual magnetization and coercive force Clicker Question 1 If this sphere is uniformly charged, it must be N A. positive B. negative C. neutral S Answers 1A Class 29 Today we will: •learn about threads and stubs of accelerating point charges. • learn that accelerating charges produce radiation (except in quantum mechanics). • learn the characteristics of radiation fields. Clicker Question 1 If a charged particle has velocity in the +x direction, but acceleration in the –x direction: A.the threads get smaller in time B.the threads get larger in time C. I don’t want to think about it, it’s almost Thanksgiving. Clicker Question 2 If a charged particle has velocity in the +x direction, but acceleration in the –x direction: A.the threads become perpendicular to the head line B.the threads become parallel to the head line Clicker Question 3 If a charged particle has velocity in the +x direction, but acceleration in the –x direction: A.the direction of the thread is the same as when the particle’s acceleration is in the +x direction B.the direction of the thread is in the opposite direction to that when the particle’s acceleration is in the +x direction Answers 1B 2A 3B Class 30 Today we will: •learn how accelerating charges affect circuits in significance ways •learn about induced electric fields •learn about induced magnetic fields and displacement current •learn Faraday’s Law •learn Maxwell’s Term of Ampere’s Law Clicker Problem 1 What is the direction of the electric acceleration field? A.right P B.left C.in R D.out E.up a i Clicker Problem 2 What is the direction of the magnetic acceleration field? A.right P B.left C.in R D.out E.up a i Clicker Problem 3 What is the direction of E B ? A. right B. left P C. in D. out R E. up a i Answers 1B 2D 3E Class 31 Today we will: • learn about EMF • learn how Faraday’s law works • learn Lenz’s Law and how to apply it Clicker Question 1 What happens if all sides of the loop move together? A. Current flows. B. Current doesn’t flow. B v v Clicker Question 2 • The external B is into the screen and is constant. • A copper wire is placed in the field and rotated about the axis shown. In what direction is the induced current? A. cw B. ccw C. depends on the direction of rotation x x x x x x x x x x x x x x x x Bexternal Answers 1B 2A Class 32 Today we will: • work several Faraday’s law problems • learn about Eddy currents Class 32 No new questions… Class 33 Today we will: •learn how motors and generators work •learn about split commutators and their use in DC motors and generators Clicker Question 1 The flux through the loop is: A. B BA B. B B cos C. B A cos D. B AB cos B A Clicker Question 2 If we rotate the handle with angular speed , A. t B. / t C. t / B A Clicker Question 3 If we rotate the handle with angular speed , the EMF is: A. BA cos t B. BA sin t C. BA sin t D. BA E. sin t BA sin t B A Answers 1D 2A 3B Class 34 Today we will: •learn about inductors and inductance •learn how to add inductors in series and parallel •learn how inductors store energy •learn how magnetic fields store energy •learn about simple LR circuits Clicker Question 1 The direction of induced current will be A.always opposite the direction of the current from the battery. B. always in the direction of the current from the battery. V C. possibly in either direction. N L R Clicker Question 2 The inductive time constant will be proportional to A. LR B. L/R C. R/L D. 1/(LR) Answers 1C 2B Class 35 Today we will: •learn more about LR circuits •learn the LR time constant •learn about LC circuits and oscillation •learn about phase angles Clicker Question 1 The voltage around the circuit loop at any given time must be: A. positive B. negative C. zero V L R Clicker Question 2 If the current is decreasing, the inductor will V A. cause the current to decrease faster B. cause the current to R decrease more slowly C. not affect the rate the current decreases 1 2 L Answers 1C 2B Class 36 Today we will: •learn about phasors •define capacitive and inductive reactance •learn about impedance •apply Kirchoff’s laws to AC circuits Clicker Question 1 The phasor to the right represents: A. B. C. D. E. 1.5 sin 60 2.7 sin 30 3 sin 30 3 cos 30 None of the above Clicker Question 2 Which of the following is a phasor diagram for a capacitor, and inductor, and a resistor in series? Blue is voltage, red is current. A. B. C. D. Answers 1C 2C Class 37 Today we will: • study the series LRC circuit in detail. • learn the resonance condition • learn what happens at resonance • calculate power in AC circuits Clicker Question 1 What is the same for each element in the circuit? 0 A. The magnitude of the voltage B. The magnitude of the current C. The current phasor D.The voltage phasor R i L C Answers 1C Class 38 Today we will: • find out how transformers work • learn about how electrical power is generated and delivered to our homes. Clicker Question 1 A transformer has 100 turns in its primary coil and 200 turns in its secondary coil. The voltage across the primary coil is 12.0 V. The voltage across the secondary coil is: A. 3.0 V B. 6.0 V C. 12.0 V D. 24.0 V E. 48.0 V Clicker Question 2 A step up transformer provides greater voltage in the primary and the secondary. This implies that A. energy is not conserved in electrical circuits. B. energy is not conserved in transformers. C. the secondary cannot provide as much current as the primary. D. the secondary can provide more current than the primary. Answers 1D 2C Class 39 Today we will: • learn about wires used in homes • learn how switches and outlets are wired • learn how to wire a 3-way switch • find out about safety devices: grounds, GFCI’s, and AFCI’s Clicker Question 1 If one switch is up and the other is down: A. the light is off. B. the light is on. C. It depends on which switch is up and which is down. down down Clicker Question 2 Most of the current flows: big resistance A. through the ground wire B. through you C. through the toast D. you are toast small resistance Answers 1A 2A Class 40 Today we will: • review basic characteristics of waves • introduce definitions of wave terminology • show how Maxwell’s Equations predict electromagnetic waves • discuss the spectrum of electromagnetic radiation • learn how radio antennas send and receive signals Clicker Question 1 If a wave has a wavenumber of k=4, what is its wavelength? A. B. C. D. E. π/4 π/2 π 2π 4π Clicker Question 2 What is the wavelength of an FM radio wave that has a frequency of 100 MHz? A. 3 m B. 3 cm C. 3 mm D. 3 μm E. 3 nm Answers 1B 2A Class 41 Today we will: • learn how digital information is transmitted on electromagnetic waves • learn the meaning of polarization • learn about polarized light and its applications Clicker Question 1 Which figure best represents the wave along the z axis? C A B D Red is E, blue is B. Clicker Question 2 Unpolarized light passes through 1)a polarizing filter 2)a second polarizing filter at 45° with respect to 1. 3)a third polarizing filter at 45° with respect to 2. Does any light emerge? A. yes B. no Answers 1C 2A