Magnets and Magnetic Fields Magnets Magnets attract iron-containing

Magnets and Magnetic Fields Magnets Magnets attract iron-containing objects. Magnets have two distinct poles called the north pole and the south pole. These names are derived from a magnets behavior on Earth. Like poles of magnets repel each other; unlike poles attract each other. Magnets and Magnetic Fields Magnetic Domains

Magnetic Domain A region composed of a group of atoms whose magnetic fields are aligned in the same direction is called a magnetic domain. Some materials can be made into permanent magnets. Soft magnetic materials (for example iron) are easily magnetized but tend to lose their magnetism easily. Hard magnetic materials (for example nickel) tend to retain their magnetism. Magnets and Magnetic Fields

Magnetic Fields A magnetic field is a region in which a magnetic force can be detected. Magnetic field lines can be drawn with the aid of a compass. Magnets and Magnetic Fields Magnetic Field of a Bar Magnet Magnets and Magnetic Fields

Magnetic Fields, continued Earths magnetic field is similar to that of a bar magnet. The magnetic south pole is near the Geographic North Pole. The magnetic north pole is near the Geographic South Pole. Magnetic declination is a measure of the difference between true north and north indicated by a compass. Magnets and Magnetic Fields Earths Magnetic Field

Magnetism from Electricity Magnetic Field of a Current-Carrying Wire A long, straight, current-carrying wire has a cylindrical magnetic field. Compasses can be used to shown the direction of the magnetic field induced by the wire. The right-hand rule can be used to determine the direction of the magnetic field in a current-carrying wire. Magnetism from Electricity

The Right-Hand Rule Magnetism from Electricity Magnetic Field of a Current-Carrying Wire Magnetism from Electricity Magnetic Field of a Current-Carrying Wire Negative Current

Zero Current Positive Current Magnetism from Electricity Magnetic Field of a Current Loop Solenoids produce a strong magnetic field by combining several loops. A solenoid is a long, helically wound coil of insulated wire. Magnetic Force

Charged Particles in a Magnetic Field A charge moving through a magnetic field experiences a force proportional to the charge, velocity, and the magnetic field. B Fmagnetic qv magnetic force on a charged particle magnetic field = (magnitude of charge)(speed of charge)

Magnetic Force Charged Particles in a Magnetic Field, continued The direction of the magnetic force on a moving charge is always perpendicular to both the magnetic field and the velocity of the charge. An alternative right-hand rule can be used to find the direction of the magnetic force. A charge moving through a magnetic field follows a circular path.

Magnetic Force Alternative Right-Hand Rule: Force on a Moving Charge Magnetic Force Sample Problem Particle in a Magnetic Field A proton moving east experiences a force of 8.8 1019 N upward due to the Earths magnetic field.At this location, the field has a magnitude of 5.5 105 T to the north. Find the speed of the particle.

Magnetic Force Sample Problem, continued Particle in a Magnetic Field Given: q = 1.60 1019 C B = 5.5 105 T Fmagnetic = 8.8 1019 N Unknown: v=? Magnetic Force

Sample Problem, continued Particle in a Magnetic Field Use the definition of magnetic field strength. Rearrange to solve for v. B v Fmagnetic qv Fmagnetic qB

8.8 19 19 N (1.60 19 19 )(5.5 10 5 ) v 1.0 105 m/s Magnetic Force Magnetic Force on a Current-Carrying Conductor A current-carrying wire in an external magnetic field undergoes a magnetic force.

The force on a current-carrying conductor perpendicular to a magnetic field is given by: magnitude of magnetic force = (magnitude of magnetic field) (current) (length of conductor within B)) Magnetic Force Force on a Current-Carrying Wire in a Magnetic Field Magnetic Force

Magnetic Force on a Current-Carrying Conductor, continued Two parallel current-carrying wires exert a force on one another that are equal in magnitude and opposite in direction. If the currents are in the same direction, the two wires attract one another. If the currents are in opposite direction, the wires repel one another. Loudspeakers use magnetic force to produce sound. Magnetic Force

Force Between Parallel Conducting Wires Magnetic Force Sample Problem Force on a Current-Carrying Conductor A wire 36 m long carries a current of 22 A from east to west. If the magnetic force on the wire due to Earths magnetic field is downward (toward Earth) and has a magnitude of 4.0 102 N, find the magnitude and direction of the magnetic field at this location.

Magnetic Force Sample Problem, continued Force on a Current-Carrying Conductor Given: I = 22 A Fmagnetic = 4.0 102 N Unknown: B=? Magnetic Force Sample Problem, continued

Force on a Current-Carrying Conductor Use the equation for the force on a current-carrying conductor perpendicular to a magnetic field. Rearrange to solve for B. Magnetic Force Sample Problem, continued Force on a Current-Carrying Conductor Using the right-hand rule to find the direction of B, face north with your thumb pointing to the west (in the direction of the current) and the palm of your hand down (in the direction of the force). Your fingers point

north. Thus, Earths magnetic field is from south to north. Multiple Choice 1. Which of the following statements best describes the domains in unmagnetized iron? A. There are no domains. B. There are domains, but the domains are smaller than in magnetized iron. C. There are domains, but the domains are oriented randomly. D. There are domains, but the domains are not magnetized.

Multiple Choice, continued 1. Which of the following statements best describes the domains in unmagnetized iron? A. There are no domains. B. There are domains, but the domains are smaller than in magnetized iron. C. There are domains, but the domains are oriented randomly. D. There are domains, but the domains are not magnetized. Multiple Choice, continued

2. Which of the following statements is most correct? F. The north pole of a freely rotating magnet points north because the magnetic pole near the geographic North Pole is like the north pole of a magnet. G. The north pole of a freely rotating magnet points north because the magnetic pole near the geographic North Pole is like the south pole of a magnet. H. The north pole of a freely rotating magnet points south because the magnetic pole near the geographic South Pole is like the north pole of a magnet. J. The north pole of a freely rotating magnet points south because the magnetic pole near the geographic South Pole is like the south pole of a magnet.

Multiple Choice, continued 2. Which of the following statements is most correct? F. The north pole of a freely rotating magnet points north because the magnetic pole near the geographic North Pole is like the north pole of a magnet. G. The north pole of a freely rotating magnet points north because the magnetic pole near the geographic North Pole is like the south pole of a magnet. H. The north pole of a freely rotating magnet points south because the magnetic pole near the geographic South Pole is like the north pole of a magnet. J. The north pole of a freely rotating magnet points south

because the magnetic pole near the geographic South Pole is like the south pole of a magnet. Multiple Choice, continued 3. If you are standing at Earths magnetic north pole and holding a bar magnet that is free to rotate in three dimensions, which direction will the south pole of the magnet point? A. straight up B. straight down C. parallel to the ground, toward the north D. parallel to the ground, toward the south

Multiple Choice, continued 3. If you are standing at Earths magnetic north pole and holding a bar magnet that is free to rotate in three dimensions, which direction will the south pole of the magnet point? A. straight up B. straight down C. parallel to the ground, toward the north D. parallel to the ground, toward the south Multiple Choice, continued 4. How can you increase the strength of a magnetic field inside a solenoid?

F. increase the number of coils per unit length G. increase the current H. place an iron rod inside the solenoid J. all of the above Multiple Choice, continued 4. How can you increase the strength of a magnetic field inside a solenoid? F. increase the number of coils per unit length G. increase the current H. place an iron rod inside the solenoid J. all of the above

Multiple Choice, continued 5. How will the electron move once it passes into the magnetic field? A. It will curve to the right and then continue moving in a straight line to the right. B. It will curve to the left and then continue moving in a straight line to the left. C. It will move in a clockwise circle. D. It will move in a counterclockwise circle.

Multiple Choice, continued 5. How will the electron move once it passes into the magnetic field? A. It will curve to the right and then continue moving in a straight line to the right. B. It will curve to the left and then continue moving in a straight line to the left. C. It will move in a clockwise circle. D. It will move in a

counterclockwise circle. Multiple Choice, continued 6. What will be the magnitude of the force on the electron once it passes into the magnetic field? F. qvB G. qvB H. qB/v J. Multiple Choice, continued

6. What will be the magnitude of the force on the electron once it passes into the magnetic field? F. qvB G. qvB H. qB/v J. Multiple Choice, continued 7. An alpha particle (q = 3.2 1019 C) moves at a speed of 2.5 106 m/s perpendicular to a magnetic field of strength 2.0 104 T. What is the magnitude

of the magnetic force on the particle? A. 1.6 1016 N B. 1.6 1016 N C. 4.0 109 N D. zero Multiple Choice, continued 7. An alpha particle (q = 3.2 1019 C) moves at a speed of 2.5 106 m/s perpendicular to a magnetic field of strength 2.0 104 T. What is the magnitude of the magnetic force on the particle? A. 1.6 1016 N B. 1.6 1016 N

C. 4.0 109 N D. zero Multiple Choice, continued Use the passage below to answer questions 89. A wire 25 cm long carries a 12 A current from east to west. Earths magnetic field at the wires location has a magnitude of 4.8 105 T and is directed from south to north. 8. What is the magnitude of the magnetic force on the wire? F. 2.3 105 N G. 1.4 104 N

H. 2.3 103 N J. 1.4 102 N Multiple Choice, continued Use the passage below to answer questions 89. A wire 25 cm long carries a 12 A current from east to west. Earths magnetic field at the wires location has a magnitude of 4.8 105 T and is directed from south to north. 8. What is the magnitude of the magnetic force on the wire? F. 2.3 105 N G. 1.4 104 N

H. 2.3 103 N J. 1.4 102 N Multiple Choice, continued Use the passage below to answer questions 89. A wire 25 cm long carries a 12 A current from east to west. Earths magnetic field at the wires location has a magnitude of 4.8 105 T and is directed from south to north. 9. What is the direction of the magnetic force on the wire? A. north B. south

C. up, away from Earth D. down, toward Earth Multiple Choice, continued Use the passage below to answer questions 89. A wire 25 cm long carries a 12 A current from east to west. Earths magnetic field at the wires location has a magnitude of 4.8 105 T and is directed from south to north. 9. What is the direction of the magnetic force on the wire? A. north B. south

C. up, away from Earth D. down, toward Earth Multiple Choice, continued Wire 1 carries current I1 and creates magnetic field B1. Wire 2 carries current I2 and creates magnetic field B2.

10. What is the direction of the magnetic field B)1 at the location of wire 2? F. to the left G. to the right H. into the page J. out of the page Multiple Choice, continued Wire 1 carries current I1 and

creates magnetic field B1. Wire 2 carries current I2 and creates magnetic field B2. 10. What is the direction of the magnetic field B)1 at the location of wire 2? F. to the left G. to the right H. into the page

J. out of the page Multiple Choice, continued Wire 1 carries current I1 and creates magnetic field B1. Wire 2 carries current I2 and creates magnetic field B2.

11. What is the direction of the force on wire 2 as a result of B)1? A. to the left B. to the right C. into the page D. out of the page Multiple Choice, continued Wire 1 carries current I1 and creates magnetic field B1.

Wire 2 carries current I2 and creates magnetic field B2. 11. What is the direction of the force on wire 2 as a result of B)1? A. to the left B. to the right C. into the page D. out of the page

Multiple Choice, continued B 2 I 22 Wire 1 carries current I1 and creates magnetic field B1. Wire 2 carries current I2 and

creates magnetic field B2. 12. What is the magnitude of the magnetic force on wire 2? Multiple Choice, continued B1 I11 B1 I 12 B1 I 2 2 B2 I 2 2

Wire 1 carries current I1 and creates magnetic field B1. Wire 2 carries current I2 and creates magnetic field B2. 12. What is the magnitude of the magnetic force on wire 2? Short Response 13. Sketch the magnetic field lines around a bar

magnet. Short Response, continued 13. Sketch the magnetic field lines around a bar magnet. Answer: Short Response, continued 14. Describe how to use the right-hand rule to determine the direction of a magnetic field around a current-carrying wire. Short Response, continued

14. Describe how to use the right-hand rule to determine the direction of a magnetic field around a current-carrying wire. Answer: Imagine wrapping the fingers of your right hand around the wire and pointing your thumb in the direction of the current. The magnetic field lines form concentric circles that are centered on the wire and curve in the same direction as your fingers. Short Response, continued 15. Draw a diagram showing the path of a positively charged particle moving in the plane of a piece of paper if a uniform magnetic field is coming out of the

page. Short Response, continued 15. Draw a diagram showing the path of a positively charged particle moving in the plane of a piece of paper if a uniform magnetic field is coming out of the page. Answer: Magnetism from Electricity Magnetic Field of a Current Loop

Electricity from Magnetism Electromagnetic Induction Electromagnetic induction is the process of creating a current in a circuit by a changing magnetic field. A change in the magnetic flux through a conductor induces an electric current in the conductor. The separation of charges by the magnetic force induces an emf. Electricity from Magnetism

Electromagnetic Induction in a Circuit Loop Electricity from Magnetism Electromagnetic Induction, continued The angle between a magnetic field and a circuit affects induction. A change in the number of magnetic field lines induces a current.

Electricity from Magnetism Characteristics of Induced Current Lenzs Law The magnetic field of the induced current is in a direction to produce a field that opposes the change causing it. Note: the induced current does not oppose the applied field, but rather the change in the applied field. Electricity from Magnetism

Characteristics of Induced Current, continued The magnitude of the induced emf can be predicted by Faradays law of magnetic induction. Faradays Law of Magnetic Induction M emf N t average induced emf = the number of loops in the circuit the time rate of change in the magnetic flux

The magnetic flux is given by M = ABcos Electricity from Magnetism Sample Problem Induced emf and Current A coil with 25 turns of wire is wrapped around a hollow tube with an area of 1.8 m2. Each turn has the same area as the tube. A uniform magnetic field is applied at a right angle to the plane of the coil. If the field increases uniformly from 0.00 T to 0.55 T in

0.85 s, find the magnitude of the induced emf in the coil. If the resistance in the coil is 2.5 , find the magnitude of the induced current in the coil. Electricity from Magnetism Sample Problem, continued Induced emf and Current 1. Define Given: t = 0.85 s A = 1.8 m2 N = 25 turns

R = 2.5 Bi = 0.00 T = 0.00 Vs/m2 Bf = 0.55 T = 0.55 Vs/m2 Unknown: emf = ? I=? = 0.0 Electricity from Magnetism Sample Problem, continued Induced emf and Current

1. Define, continued Diagram: Show the coil before and after the change in the magnetic field. Electricity from Magnetism Sample Problem, continued Induced emf and Current 2. Plan Choose an equation or situation. Use Faradays law of magnetic induction to find the induced emf in the coil. AB cos

M emf N N t t Substitute the induced emf into the definition of resistance to determine the induced current in the coil. emf I R Electricity from Magnetism

Sample Problem, continued Induced emf and Current 2. Plan, continued Rearrange the equation to isolate the unknown. In this example, only the magnetic field strength changes with time. The other components (the coil area and the angle between the magnetic field and the coil) remain constant. B emf NA cos t

Electricity from Magnetism Sample Problem, continued Induced emf and Current 3. Calculate Substitute the values into the equation and solve. Vs 0.55 0.00 2

m emf (25)(1.8 m2 )(cos0.0 ) 29 V (0.85 s) 29 V I 12 A 2.5 emf 29 V I 12 A

Electricity from Magnetism Sample Problem, continued Induced emf and Current 4. Evaluate The induced emf, and therefore the induced current, is directed through the coil so that the magnetic field produced by the induced current opposes the change in the applied magnetic field. For the diagram shown on the previous page, the induced magnetic field is directed to the right and the current that produces it is

directed from left to right through the resistor. Generators, Motors, and Mutual Inductance Generators and Alternating Current A generator is a machine that converts mechanical energy into electrical energy. Generators use induction to convert mechanical energy into electrical energy. A generator produces a continuously changing emf.

Generators, Motors, and Mutual Inductance Induction of an emf in an AC Generator Generators, Motors, and Mutual Inductance Generators and Alternating Current, continued Alternating current is an electric current that changes direction at regular intervals. Alternating current can be converted to direct

current by using a device called a commutator to change the direction of the current. Generators, Motors, and Mutual Inductance Motors Motors are machines that convert electrical energy to mechanical energy. Motors use an arrangement similar to that of generators. Back emf is the emf induced in a motors coil that tends to reduce the current in the coil of a motor.

Generators, Motors, and Mutual Inductance Mutual Inductance The ability of one circuit to induce an emf in a nearby circuit in the presence of a changing current is called mutual inductance. In terms of changing primary current, Faradays law is given by the following equation, where M is the mutual inductance: M I

emf N M t t AC Circuits and Transformers Objectives Distinguish between rms values and maximum values of current and potential difference. Solve problems involving rms and maximum values of current and emf for ac circuits. Apply the transformer equation to solve problems

involving step-up and step-down transformers. AC Circuits and Transformers Effective Current The root-mean-square (rms) current of a circuit is the value of alternating current that gives the same heating effect that the corresponding value of direct current does. rms Current Irms Imax

2 0.707 Imax AC Circuits and Transformers Effective Current, continued The rms current and rms emf in an ac circuit are important measures of the characteristics of an ac circuit. Resistance influences current in an ac circuit. AC Circuits and Transformers

Sample Problem rms Current and emf A generator with a maximum output emf of 205 V is connected to a 115 resistor. Calculate the rms potential difference. Find the rms current through the resistor. Find the maximum ac current in the circuit. 1. Define Given: Vrms = 205 V R = 115 Unknown: Vrms = ? Irms = ? Imax = ?

AC Circuits and Transformers Sample Problem, continued rms Current and emf 2. Plan Choose an equation or situation. Use the equation for the rms potential difference to find Vrms. Vrms = 0.707 Vmax Rearrange the definition for resistance to calculate Irms. Vrms Irms

R Use the equation for rms current to find Irms. Irms = 0.707 Imax AC Circuits and Transformers Sample Problem, continued rms Current and emf 2. Plan, continued Rearrange the equation to isolate the unknown. Rearrange the equation relating rms current to maximum current so that maximum current is calculated.

Irms Imax 0.707 AC Circuits and Transformers Sample Problem, continued rms Current and emf 3. Calculate Substitute the values into the equation and solve. Vrms (0.707)(205 V) 145 V 145 V Irms

1.26 A 115 1.26 A Imax 1.78 A 0.707 4. Evaluate The rms values for emf and current are a little more than two-thirds the maximum values, as expected. AC Circuits and Transformers Transformers

A transformer is a device that increases or decreases the emf of alternating current. The relationship between the input and output emf is given by the transformer equation. N V2 2 V1 N1 induced emf in secondary = number of turns in secondary number of turns in primary applied emf in primary

AC Circuits and Transformers Transformers, continued The transformer equation assumes that no power is lost between the primary and secondary coils. However, real transformers are not perfectly efficient. Real transformers typically have efficiencies ranging from 90% to 99%. The ignition coil in a gasoline engine is a transformer. AC Circuits and Transformers

A Step-Up Transformer in an Auto Ignition System Electromagnetic Waves Propagation of Electromagnetic Waves Electromagnetic waves travel at the speed of light and are associated with oscillating, perpendicular electric and magnetic fields. Electromagnetic waves are transverse waves; that is, the direction of travel is perpendicular to the the direction of oscillating electric and magnetic fields.

Electric and magnetic forces are aspects of a single force called the electromagnetic force. Electromagnetic Waves Propagation of Electromagnetic Waves, continued All electromagnetic waves are produced by accelerating charges. Electromagnetic waves transfer energy. The energy of electromagnetic waves is stored in the waves oscillating electric and magnetic fields. Electromagnetic radiation is the transfer of energy

associated with an electric and magnetic field. Electromagnetic radiation varies periodically and travels at the speed of light. Electromagnetic Waves The Sun at Different Wavelengths of Radiation Electromagnetic Waves Propagation of Electromagnetic Waves, continued

High-energy electromagnetic waves behave like particles. An electromagnetic waves frequency makes the wave behave more like a particle. This notion is called the wave-particle duality. A photon is a unit or quantum of light. Photons can be thought of as particles of electromagnetic radiation that have zero mass and carry one quantum of energy. Electromagnetic Waves The Electromagnetic Spectrum

The electromagnetic spectrum ranges from very long radio waves to very short-wavelength gamma waves. The electromagnetic spectrum has a wide variety of applications and characteristics that cover a broad range of wavelengths and frequencies. Electromagnetic Waves The Electromagnetic Spectrum, continued Radio Waves longest wavelengths communications, tv

Microwaves 30 cm to 1 mm radar, cell phones Infrared 1 mm to 700 nm heat, photography Visible light 700 nm (red) to 400 nm (violet)

Ultraviolet 400 nm to 60 nm disinfection, spectroscopy X rays 60 nm to 104 nm medicine, astronomy, security screening Gamma Rays less than 0.1 nm

cancer treatment, astronomy Electromagnetic Waves The Electromagnetic Spectrum Multiple Choice 1. Which of the following equations correctly describes Faradays law of induction? A. emf B. emf C. emf

D. emf ( AB tan ) N t ( AB cos ) N t ( AB cos ) N t ( AB cos ) M

t Multiple Choice, continued 1. Which of the following equations correctly describes Faradays law of induction? A. emf B. emf C. emf D. emf ( AB tan ) N t

( AB cos ) N t ( AB cos ) N t ( AB cos ) M t Multiple Choice, continued 2. For the coil shown at right, what must be done to induce a clockwise current?

F. Either move the north pole of a magnet down into the coil, or move the south pole of the magnet up and out of the coil. G. Either move the south pole of a magnet down into the coil, or move the north pole of the magnet up and out of the coil. H. Move either pole of the magnet down into the coil. J. Move either pole of the magnet up and out of the coil. Multiple Choice, continued 2. For the coil shown at right, what must be

done to induce a clockwise current? F. Either move the north pole of a magnet down into the coil, or move the south pole of the magnet up and out of the coil. G. Either move the south pole of a magnet down into the coil, or move the north pole of the magnet up and out of the coil. H. Move either pole of the magnet down into the coil. J. Move either pole of the magnet up and out of the coil. Multiple Choice, continued

3. Which of the following would not increase the emf produced by a generator? A. rotating the generator coil faster B. increasing the strength of the generator magnets C. increasing the number of turns of wire in the coil D. reducing the cross-sectional area of the coil Multiple Choice, continued 3. Which of the following would not increase the emf produced by a generator? A. rotating the generator coil faster B. increasing the strength of the generator magnets C. increasing the number of turns of wire in the coil

D. reducing the cross-sectional area of the coil Multiple Choice, continued 4. B)y what factor do you multiply the maximum emf to calculate the rms emf for an alternating current? F. 2 G. H. 2 1 1

J. 2 2 Multiple Choice, continued 4. B)y what factor do you multiply the maximum emf to calculate the rms emf for an alternating current? F. 2 G. H. 2

1 1 J. 2 2 Multiple Choice, continued 5. Which of the following correctly describes the composition of an electromagnetic wave? A. a transverse electric wave and a magnetic transverse wave that are parallel and are moving in the same direction

B. a transverse electric wave and a magnetic transverse wave that are perpendicular and are moving in the same direction C. a transverse electric wave and a magnetic transverse wave that are parallel and are moving at right angles to each other D. a transverse electric wave and a magnetic transverse wave that are perpendicular and are moving at right angles to each other Multiple Choice, continued 5. Which of the following correctly describes the composition of an electromagnetic wave?

A. a transverse electric wave and a magnetic transverse wave that are parallel and are moving in the same direction B. a transverse electric wave and a magnetic transverse wave that are perpendicular and are moving in the same direction C. a transverse electric wave and a magnetic transverse wave that are parallel and are moving at right angles to each other D. a transverse electric wave and a magnetic transverse wave that are perpendicular and are moving at right angles to each other Multiple Choice, continued

6. A coil is moved out of a magnetic field in order to induce an emf. The wire of the coil is then rewound so that the area of the coil is increased by 1.5 times. Extra wire is used in the coil so that the number of turns is doubled. If the time in which the coil is removed from the field is reduced by half and the magnetic field strength remains unchanged, how many times greater is the new induced emf than the original induced emf ? F. 1.5 times G. 2 times H. 3 times J. 6 times

Multiple Choice, continued 6. A coil is moved out of a magnetic field in order to induce an emf. The wire of the coil is then rewound so that the area of the coil is increased by 1.5 times. Extra wire is used in the coil so that the number of turns is doubled. If the time in which the coil is removed from the field is reduced by half and the magnetic field strength remains unchanged, how many times greater is the new induced emf than the original induced emf ? F. 1.5 times G. 2 times H. 3 times J. 6 times

Multiple Choice, continued Use the passage below to answer questions 78. A pair of transformers is connected in series, as shown in the figure below. 7. From left to right, what are the types of the two transformers? A. B)oth are step-down transformers.

B. B)oth are step-up transformers. C. One is a step-down transformer; and one is a step-up transformer. D. One is a step-up transformer; and one is a step-down transformer. Multiple Choice, continued Use the passage below to answer questions 78. A pair of transformers is

connected in series, as shown in the figure below. 7. From left to right, what are the types of the two transformers? A. B)oth are step-down transformers. B. B)oth are step-up transformers. C. One is a step-down transformer; and one is a step-up transformer.

D. One is a step-up transformer; and one is a step-down transformer. Multiple Choice, continued Use the passage below to answer questions 78. A pair of transformers is connected in series, as shown in the figure below. 8. What is the output potential difference from

the secondary coil of the transformer on the right? F. 400 V G. 12 000 V H. 160 000 V J. 360 000 V Multiple Choice, continued Use the passage below to answer questions 78. A pair of transformers is connected in series, as

shown in the figure below. 8. What is the output potential difference from the secondary coil of the transformer on the right? F. 400 V G. 12 000 V H. 160 000 V J. 360 000 V Multiple Choice, continued

9. What are the particles that can be used to describe electromagnetic radiation called? A. electrons B. magnetons C. photons D. protons Multiple Choice, continued 9. What are the particles that can be used to describe electromagnetic radiation called? A. electrons B. magnetons C. photons

D. protons Multiple Choice, continued 10. The maximum values for the current and potential difference in an ac circuit are 3.5 A and 340 V, respectively. How much power is dissipated in this circuit? F. 300 W G. 600 W H. 1200 W J. 2400 W Multiple Choice, continued

10. The maximum values for the current and potential difference in an ac circuit are 3.5 A and 340 V, respectively. How much power is dissipated in this circuit? F. 300 W G. 600 W H. 1200 W J. 2400 W Short Response 11. The alternating current through an electric toaster has a maximum value of 12.0 A. What is the rms value of this current?

Short Response, continued 11. The alternating current through an electric toaster has a maximum value of 12.0 A. What is the rms value of this current? Answer: 8.48 A Short Response, continued 12. What is the purpose of a commutator in an ac generator? Short Response, continued

12. What is the purpose of a commutator in an ac generator? Answer: It converts ac to a changing current in one direction only. Short Response, continued 13. How does the energy of one photon of an electromagnetic wave relate to the waves frequency? Short Response, continued 13. How does the energy of one photon of an electromagnetic wave relate to the waves frequency?

Answer: The energy is directly proportional to the waves frequency (E = hf ). Short Response, continued 14. A transformer has 150 turns of wire on the primary coil and 75 000 turns on the secondary coil. If the input potential difference across the primary is 120 V, what is the output potential difference across the secondary? Short Response, continued 14. A transformer has 150 turns of wire on the primary

coil and 75 000 turns on the secondary coil. If the input potential difference across the primary is 120 V, what is the output potential difference across the secondary? Answer: 6.0 104 V Extended Response 15. Why is alternating current used for power transmission instead of direct current? B)e sure to include power dissipation and electrical safety considerations in your answer.

Extended Response, continued 15. Answer: For electric power to be transferred over long distances without a large amount of power dissipation, the electric power must have a high potential difference and low current. However, to be safely used in homes, the potential difference must be lower than that used for long-distance power transmission. B)ecause of induction, the potential difference and current of electricity can be transformed to higher or lower values, but the current must change continuously (alternate) for this to happen.

Extended Response, continued Base your answers to questions 16. Why must the current enter 1618 on the information below. the coil just as someone comes up to the table? A device at a carnivals haunted house involves a metal ring that flies upward from a table when a patron passes near the tables edge. The device consists of a photoelectric switch that activates

the circuit when anyone walks in front of the switch and of a coil of wire into which a current is suddenly introduced when the switch is triggered. Extended Response, continued Base your answers to questions 16. Why must the current enter 1618 on the information below. the coil just as someone comes up to the table? A device at a carnivals haunted

house involves a metal ring that flies upward from a table when a Answer: The change in current in the coil will produce a patron passes near the tables changing magnetic field, edge. The device consists of a which will induce a current in photoelectric switch that activates the ring. The induced current the circuit when anyone walks in produces a magnetic field front of the switch and of a coil of that interacts with the

wire into which a current is magnetic field from the coil, suddenly introduced when the causing the ring to rise from switch is triggered. the table. Extended Response, continued Base your answers to questions 17. Using Lenzs law, explain 1618 on the information below. why the ring flies upward when there is an increasing

A device at a carnivals haunted current in the coil? house involves a metal ring that flies upward from a table when a patron passes near the tables edge. The device consists of a photoelectric switch that activates the circuit when anyone walks in front of the switch and of a coil of wire into which a current is suddenly introduced when the switch is triggered.

Extended Response, continued Base your answers to questions 17. Using Lenzs law, explain why the ring flies upward 1618 on the information below. when there is an increasing A device at a carnivals haunted current in the coil? house involves a metal ring that flies upward from a table when a Answer: According to Lenzs law, patron passes near the tables the magnetic field induced in

edge. The device consists of a the ring must oppose the photoelectric switch that activates magnetic field that induces the circuit when anyone walks in the current in the ring. The front of the switch and of a coil of opposing fields cause the ring, which can move freely, wire into which a current is to rise upward from the coil suddenly introduced when the under the tables surface.

switch is triggered. Extended Response, continued Base your answers to questions 1618 on the information below. A device at a carnivals haunted house involves a metal ring that flies upward from a table when a patron passes near the tables edge. The device consists of a photoelectric switch that activates the circuit when anyone walks in front of the switch and of a coil of

wire into which a current is suddenly introduced when the switch is triggered. 18. Suppose the change in the magnetic field is 0.10 T/s. If the radius of the ring is 2.4 cm and the ring is assumed to consist of one turn of wire, what is the emf induced in the ring?

Extended Response, continued Base your answers to questions 1618 on the information below. A device at a carnivals haunted house involves a metal ring that flies upward from a table when a patron passes near the tables edge. The device consists of a photoelectric switch that activates the circuit when anyone walks in front of the switch and of a coil of wire into which a current is suddenly introduced when the

switch is triggered. 18. Suppose the change in the magnetic field is 0.10 T/s. If the radius of the ring is 2.4 cm and the ring is assumed to consist of one turn of wire, what is the emf induced in the ring? Answer: 1.8 104 V Electricity from Magnetism

Ways of Inducing a Current in a Circuit

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