SI leader: Rosalie Dubberke Physics 222 Exam 2 review SI leader: Rosalie Dubberke

Topics: Kirchhoff’s laws Magnetic Fields and Forces Magnetic Flux LC/LR/LRC circuits AC power sources Mutual Inductance

What are Kirchhoff’s laws? The sum of voltage drops through any loop are equal to zero The sum of currents going into any junction must equal the sum of the currents leaving it How can we use these?

Question from Fall 2014 exam 𝑅 1 =5 𝑂ℎ𝑚𝑠 𝑅 2 =10 𝑂ℎ𝑚𝑠 r = 1 Ohm ε= 9V Find the voltage drop across 𝑅 2 ?

Magnetic Fields

Question from Fall 2014 Exam An electron moving with a velocity = 5.0 × 10 7 m/s enters a region of space where perpendicular electric and a magnetic fields are present. The electric field is E = 1j. What magnetic field will allow the electron to go through the region without being deflected?

Question from fall 2013 exam 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,

Magnetism and Current

Question from Fall 2013 exam The three loops of wire shown in the figure are 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?

Question from a past exam 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?

Induced Current and Mutual inductance Two coils have mutual inductance of M= 3.25× 10 −4 H. The current 𝐼 1 in the first coil increases at a uniform rate of 860 A/s. What is the magnitude of the induced emf in the second coil? Suppose that the current described is in the second coil rather than the first. What is the magnitude of the induced emf in the first coil?

Magnetic Flux

Question from Fall 2013 exam 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?

LR, LC, and LRC circuits

Question from the 2013 Fall Exam 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?

Question from the 2013 Exam In a series LRC circuit, the frequency at which the circuit is at resonance is 𝑓 0 . If you double the resistance, the inductance, the capacitance, and the voltage amplitude of the ac source, what is the new resonance frequency?

AC Power Source

Some helpful equations for AC power sources (I would write these on my equation sheet very clearly so that they are easy to understand)

Question from Past exam The 60-Hz ac source of a series circuit has a voltage amplitude of 120 V. The resistance, capacitive reactance, and inductive reactance are as shown in the figure. What is the rms current in the circuit? (rms current is the root mean square current, so it’s 𝐼 𝑟𝑚𝑠 = 𝐼 𝑚𝑎𝑥 2 )

More Questions for practice

When the current in a toroidal solenoid is changing at a rate of 0 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 mV. When the current equals 1.40 A, the average flux through each turn of the solenoid is 2.8 mWb. How many turns does the solenoid have?

Question from fall 2013 Exam 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?

Question from a past exam A 4.0 mH coil carries a current of 5.0 A. How much magnetic field energy is stored in the coil's magnetic field?

Problem from a past exam 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.

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?

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)

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?

Questions?