Physics 236 Topic Checklist

Unit II

At the end of each chapter make sure that you are familiar with all the listed topics and most importantly that you can do the homework problems associated with them.

 

Chapter 27: Electric Current is the flow of electric charge. The direction of the current is the direction positive carriers move.

q       Unit is the ampere (A).

A = C/s

q       Carriers and Drift Velocity  Electrons in metals, but could be positive or negative in electrolytes and semiconductors.

q       Current Density  Current per unit area. (A/m²)

 

q       Ohm’s Law  Current flows in a conductor if a potential difference is applied. The current density in a conductor is proportional to the electric field for many substances. Resistance (W). Resistivity  (W×m) and Conductivity.

q       Temperature Dependence of Resistance

 

q       Atomic Model of Conductivity  Carriers are driven forward by the electric field and slowed down by collisions with the atoms of the conductor. This affects drift velocity and mean time between collisions.

 

q       Electrical Energy and Power

Chapter 28: DC Circuits   These are electric circuits driven by voltage sources that do not vary with time.

q       EMF, Internal Resistance, and Terminal Voltage  The output of a source is affected by the circuit it sees. Maximum power is delivered to the load if the resistance of the source matches the resistance of the load.                 

q       Resistors in Series and Parallel

ü      Resistors in series have the same current.

 

ü      Resistors in parallel have the same voltage.

 

q       Kirchhoff’s Rules  Use this method if a circuit cannot be broken down into purely series and parallel connections.

ü      Current Rule: The sum of the currents entering a junction equals the sum of the currents leaving the junction.

ü      Voltage Rule: The sum of the voltages (accounting for polarity) around a closed circuit loop is zero.

q       RC Circuits;  Time constants.

ü      Charging:

ü      Discharging:

 

q       Electrical Meters   Know how to use power supplies, ammeters and voltmeters in the laboratory.

ü      Ammeter: Connect ammeters in series with the component(s) to be measured. Should have low resistance. The range is controlled by means of a parallel shunt resistor.

ü      Voltmeter: Connect voltmeters in parallel with the component(s) to be measured. Should have high resistance. The range is controlled by means of a series multiplier resistor.

Chapter 29: Magnetic Fields are produced by and exert force on moving charges.

q       Force Law  The magnetic force on a moving charge

 

q       Unit is the Tesla (T)

T = N^.s/kg^.m

q       Magnet Force on a Current Element

 

q       Torque on a Current Loop;  Magnetic Dipole Moment (A×m²)

 

q       Circular Orbits  Since the magnetic force is perpendicular to the velocity, it causes charges to move in circular paths.

q       Cyclotron  This is a device used in research labs to accelerate charged particles.

 

 

Chapter 30: Sources of Magnetic Fields

q       Magnetic Field of a Current Element (Law of Biot and Savart)

 

q       Field Lines and Right Hand Rules  Magnetic field lines form closed loops. Learn the right hand rules for determining the direction of the magnetic field produced by various sources.

q       Special Cases  Refer these formulas to the corresponding figures in the texybook.

ü      Straight Wire

ü      Long Straight Wire

ü      Current Loop

q       Amperes Law relates the magnetic field to its source current. It can be used to find the magnetic field for sources with a high degree of symmetry.

 

q       Torroids and Solenoids

q       Magnetic Flux is the number of magnetic field lines passing through an area.

 

q       Gauss’s Law for Magnetism Since magnetic field lines do not begin or end

 

q       Displacement Current  Magnetic field is produced by a changing electric field as well as by an ordinary current. Displacement current represents the changing electric field.

 

 

q       Generalized Ampere’s Law includes displacement current as well as ordinary current.

 

q       Magnetization in Matter,  Magnetization, and Magnetic Field Strength

 

 

§         B is the total magnetic field.

§         B₀ and H represent the contribution made by real currents.

§         M is the contribution made by atomic dipoles in the material.

q       Magnetic Susceptibility and Permeability

 

q       Types of Magnetic Materials

ü      Paramagnetic: m > m_o

ü      Diamagnetic: m < m_o

ü      Ferromagnetic: m >> m_o

q       Ferromagnetism  Ferromagnetic materials can be “permanently” magnetized.

Alignment of atomic dipoles into domains.

ü      B >> B₀

ü      Hysteresis.