PHYSICS 222 EXAM 2 REVIEW SI LEADER ROSALIE

PHYSICS 222 EXAM 2 REVIEW SI LEADER: ROSALIE DUBBERKE

TOPICS: • Magnetic Fields and Forces • Magnetic Flux • LC/LR/LRC circuits • AC power sources • Mutual Inductance

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• Three particles travel through a region of space where the magnetic field is out of the page, as shown in the figure. The electric charge of each of the three particles is, respectively,

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• The figure shows a velocity selector that can be used to measure the speed of a charged particle. A beam of particles is directed along the axis of the instrument. A parallel plate capacitor sets up an electric field E, which is oriented perpendicular to a uniform magnetic field B. If the plates are separated by 2. 0 mm and the value of the magnetic field is 0. 60 T, what voltage between the plates will allow particles of speed 5. 0 × 105 m/s to pass straight through without deflection?

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When an external magnetic field is applied along a positive z – direction to a diamagnetic material, the magnetic moment induced inside the material • A) points in a positive (+z) – direction • B) points in a negative (–z) – direction • C) iz zero • D) points in a positive (+x) - direction • E) is somewhere in the xy-plane (perpendicular to the z-direction)

LETS SOLVE IT When an external magnetic field is applied along a positive z – direction to a diamagnetic material, the magnetic moment induced inside the material • A) points in a positive (+z) – direction • B) points in a negative (–z) – direction • C) iz zero • D) points in a positive (+x) - direction • E) is somewhere in the xy-plane (perpendicular to the z-direction) By definition, magnetic moment in the diamagnetic material opposes the applied field, so it will be in a negative (-z) – direction

A capacitor is charging in a simple RC circuit with a dc battery. Which one of the following statements about this capacitor is accurate? • A) The magnetic field between the capacitor plates is increasing with time because the charge on the plates is increasing. • B) There is a magnetic field between the capacitor plates because charge travels between the plates by jumping from one plate to the other. • C) There is no magnetic field between the capacitor plates because no charge travels between the plates. • D) There is a magnetic field between the capacitor plates, even though no charge travels between them, because the magnetic flux between the plates is changing. • E) There is a magnetic field between the capacitor plates, even though no charge travels between them, because the electric flux between the plates is changing.

LETS SOLVE IT! • E is the correct answer! • Why? As the charge on the capacitor is changing, the electric field between the two plates is changing, leading to a changing electric flux, which generates a magnetic field. However, it is important to realize that there is no actual charge moving between the plates.

• The three loops of wire shown in the figure all subject to the same uniform magnetic field that does not vary with time. Loop 1 oscillates back and forth as the bob in a pendulum, loop 2 rotates about a vertical axis, and loop 3 oscillates up and down at the end of a spring. Which loop, or loops, will have an emf induced in them?

HINT: •

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• Two round concentric metal wires lie on a tabletop, one inside the other. The inner wire has a diameter of 22. 0 cm and carries a clockwise current of 16. 0 A, as viewed from above, and the outer wire has a diameter of 36. 0 cm. • What must be the direction (as viewed from above) of the current in the outer wire so that the net magnetic field due to this combination of wires is zero at the common center of the wires?

LETS SOLVE IT • Two round concentric metal wires lie on a tabletop, one inside the other. The inner wire has a diameter of 22. 0 cm and carries a clockwise current of 16. 0 A, as viewed from above, and the outer wire has a diameter of 36. 0 cm. • What must be the direction (as viewed from above) of the current in the outer wire so that the net magnetic field due to this combination of wires is zero at the common center of the wires? It should be counterclockwise. The first coils creates a magnetic field vector going into the table, so the second wire needs to create a magnetic field vector coming out of the table to balance it. This means it should have a counterclockwise current

• The figure shows four different sets of insulated wires that cross each other at right angles without actually making electrical contact. The magnitude of the current is the same in all the wires, and the directions of current flow are as indicated. For which (if any) configurations will the magnetic field at the center of the square formed by the wires be equal to zero?

LETS SOLVE IT We know the current through each of the wires is the same, which means they are creating magnetic fields (following the right hand rule) of equal magnitude. Next, we need to balance the directions C is the only possible correct answer, because it is the only one where it has 2 magnetic field vectors going “into” it and 2 coming “out” of it.

• Two long parallel wires placed side-by-side on a horizontal table carry identical size currents in opposite directions. The wire on your right carries current toward you, and the wire on your left carries current away from you. From your point of view, the magnetic field at the point exactly midway between the two wires

LETS SOLVE IT • Two long parallel wires placed side-by-side on a horizontal table carry identical size currents in opposite directions. The wire on your right carries current toward you, and the wire on your left carries current away from you. From your point of view, the magnetic field at the point exactly midway between the two wires • We can use the right hand rule to determine that the magnetic field should be into the table.

A circular coil lies flat on a horizontal table. A bar magnet is held above its center with its North Pole pointing down. The magnet is fixed and does not move. What kind of current does it induce in what direction?

LETS SOLVE IT A circular coil lies flat on a horizontal table. A bar magnet is held above its center with its North Pole pointing down. The magnet is fixed and does not move. What kind of current does it induce in what direction? It induces no current! The magnet isn’t moving, the coil isn’t moving, so there is no change in flux, meaning no current.

An L-shaped metal machine part is made of two equal-length segments that are perpendicular to each other and carry a 4. 50 -A current as shown in the figure. This part has a total mass of 3. 80 kg and a total length of 3. 00 m, and it is in an external 1. 20 -T magnetic field that is oriented perpendicular to the plane of the part, as shown. What is the magnitude of the NET magnetic force that the field exerts on the part?

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A 2. 0 -m long conducting wire is formed into a square and placed in the horizontal xy plane. A uniform magnetic field is oriented 30 degrees above the horizontal with a strength of 9 T. What is the magnetic flux through the square?

LETS SOLVE IT A 2. 0 -m long conducting wire is formed into a square and placed in the horizontal xy plane. A uniform magnetic field is oriented 30 degrees above the horizontal with a strength of 9 T. What is the magnetic flux through the square? 30 °

• A series LR circuit consists of a 2. 0 -H inductor with negligible internal resistance, a 100 -ohm resistor, an open switch, and a 9. 0 -V ideal power source. After the switch is closed, what is the maximum power delivered by the power supply?

HINT: • How will the inductor affect the power, knowing we want the maximum power possible?

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• There is an LC circuit with inductor L = 1 H, capacitor C = 1 F and an open switch. Initially capacitor is fully charged. Now the switch is closed. How many times the voltage on the capacitor will be zero during 341 seconds?

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HINT •

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SOME HELPFUL EQUATIONS FOR AC POWER SOURCES (I would write these on my equation sheet very clearly so that they are easy to understand)

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• When an LRC series circuit is at resonance, which of the following statements about the circuit is correct? (there may be more than one answer) • The reactance of the capacitor is zero • The reactance of the inductor is zero • The reactance due to the inductor and the capacitor is at its maximum value • The impedance is at its maximum value • The current amplitude is a maximum

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• Which of the following phasor diagrams shown below best represents a series LRC circuit at resonance?

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When the current in a toroidal solenoid is changing at a rate of 0. 03 A/s, the magnitude of the induced emf is 15 m. V. When the current equals 1. 40 A, the average flux through each turn of the solenoid is 2. 8 m. Wb. How many turns does the solenoid have?

LETS SOLVE IT When the current in a toroidal solenoid is changing at a rate of 0. 03 A/s, the magnitude of the induced emf is 15 m. V. When the current equals 1. 40 A, the average flux through each turn of the solenoid is 2. 8 m. Wb. How many turns does the solenoid have?

• A 4. 0 m. H coil carries a current of 5. 0 A. How much magnetic field energy is stored in the coil's magnetic field?

LETS SOLVE IT • A 4. 0 m. H coil carries a current of 5. 0 A. How much magnetic field energy is stored in the coil's magnetic field?

QUESTIONS?