Material Covered on Exam 1

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Background Material

You should remember the vector addition of forces from Chapter 9 and the definitions of work and energy from Chapter 6, as well as basic relationships for linear motion (Chapter 2) and circular motion (Chapter 5). These concepts are a very basic part of physics and may appear throughout the course. If you need any thermodynamic relations, they will be given. All physical constants needed will be given.

Chapter 16

Concepts:

Electric charge, Coulomb Force Law, Coulombs, charge conservation, electric conductors and insulators, electric field lines. Remember the rules for drawing electric field lines.

Equations:

Force between two charges Q, Q' :

F = kQQ'/r2.

Force on test charge q in electic field E:

F = qE.

Forces and electric fields are both vectors, and must be added using vector addition.

Units:

The unit of charge is the Coulomb (C).

Chapter 17

Concepts:

Electric potential, potential energy of charges in fields, voltage, equipotential surfaces, capacitors, Farads, dielectrics, dielectric constant K, energy stored in capacitors and electric fields. Remember the rules for drawing equipotential lines.

Equations:

Potential energy of charge q in electric potential V:

PE = q V.

Electric Potential of point charge Q:

V = kQ/r .

The definition of Capacitance:

Q = C V.

Parallel Plate Capacitance, area A, separation d, dielectric constant K:

C = K e0 A/d

Energy stored in a capacitor:

U = QV/2 = CV2/2 = Q2/(2C).

Energy density stored in an electric field:

u = Energy/Volume = e0 E2.

Units:

Electric Potential: 1 Volt = 1 Joule/Coulomb
Capacitance: 1 Farad = 1 Coulomb/Volt

Chapter 18

Concepts:

Electric current, Amperes, Ohm's Law, resistance, resistivity, electric power, direct current, alternating current, rms voltage and current, average power.

Equations:

Current due to n charges e per unit volume moving with average velocity v through a wire of cross-sectional area A:

I = neAv

Ohm's Law:

V = I R.

Resistivity r of a wire of length L and cross-sectional area A:

R = r L / A .

Dependence of resistance on temperature if the temperature coefficient of resistivity is a and the resistance at temperature T0 is R0:

RT = R0 [1 + a (T - T0)] .

Power carried by current I across a potential difference V:

P = VI = I2 R = V2/R.

AC Current:

The rms voltage is the peak voltage divided by the square root of 2.
The rms current is the peak current divided by the square root of 2.
The average power is half the peak power.

Units:

Current: 1 Ampere = 1 Coulomb/second
Resistance: 1 Ohm = 1 Volt/Ampere

Chapter 19

Concepts:

Series and parallel combinations of resistors or capacitors, Kirchoff's Rules, terminal voltage and emf, RC circuits and time constants.

Equations:

Series Resistors:

R = R1 + R2 + ...

Parallel resistors:

1/R = 1/R1 + 1/R2 + ...

Parallel Capacitors:

C = C1 + C2 + ...

Series capacitors:

1/C = 1/C1 + 1/C2 + ...

Terminal Voltage when current I flows out of a battery with given emf E and internal resistance r:

Vab = E - I r .

Kirchhoff's Junction Rule:

The sum of all currents entering a junction is zero.

Kirchhoff's Loop Rule:

The sum of all potential changes around a closed circuit is zero.

Discharging a capacitor with maximum charged voltage V0:

V(t) = V0 exp(-t/RC)

Charging a capacitor with maximum charged voltage V0:

V(t) = V0[1 - exp(-t/RC)]

The product RC is called the time constant of the RC circuit, and is in seconds if R is in Ohms and C is in Farads.

For DC circuits with capacitors, two rules are helpful when the capacitor is first connected, or when the capacitor has been connected for a long time:

Physics 222 Department of Physics University of Tennessee