This document provides an overview and review of topics covered in an AP Physics B test, including electrostatics, electric circuits, and magnetism. Key points covered are Coulomb's law, electric fields, Gauss' law, capacitance, Ohm's law, Kirchhoff's rules, and how moving charges produce magnetic fields. The review is organized into sections on electrostatics, electric potential, dielectrics and capacitors, electric current, DC circuits, and magnetism. Diagrams are provided to illustrate concepts like electric field lines, parallel plate capacitors, and Kirchhoff's rules.

1. AP Phys B
Test Review
Electrostatics, Circuits, and
Magnetism
4/29/2008

2. Overview
 Electrostatics
 Electric Potential
 Dielectrics and Capacitance
 Electric Current
 DC Circuits
 Magnetism

3. Electrostatics
 Charge is carried by subatomic particles
(protons, electrons)
• 99% of all charged effects caused by electron
transfer
 Charging by Conduction
• Physical contact
 Charging by Induction
• No physical contact

4. Coulomb’s Law
 This law determines the force of attraction or
repulsion between 2 charged objects
• ε0 is a constant – permittivity of free space
• Positive force = repulsive, negative force = attractive
• Remember: force is a vector!
F
Q Q
r
q =
1
4 0
1 2
2π ε

5. Electric field lines
 A visual
representation of
an electric field.
• More lines =
stringer force
• Point away from
positive, toward
negative.

6. Electric Fields and conductors
 The electric field inside any conductor is
zero
 The electric field is always perpendicular
to the surface of a conductor

7. Gauss’ Law
 Electric Flux: The amount of an electric field
passing through an area
 Gauss’ Law: The total electric flux passing
through a closed surface is proportional to the
charged enclosed in that surface.
Φ =
Q e n c l o s e d
ε 0
Φ = E A c o s θ

8. Electric Potential Energy
 Electric Potential energy can be determined
using mechanics
 Electric potential is defined as the electric
potential energy per unit charge
∆ U q E d= −
V
U
q
W
q
= = − ∆ ∆U q V= −

9. Equipotential lines or surfaces
 An equipotential surface is a surface
over which all points have the same
potential.
• An equipotential surface must be
perpendicular to the electric field!

10. Potential due to a point charge
V
Q
r
=
1
4 0π ε
• Remember: potential is a scalar!

11. Capacitance
 A capacitor is a device that stores electric
charge.
 The capacitance of an object is defined as:
 Capacitance is measured in farads.
C
Q
V
=

12. Parallel plate capacitors and
dielectrics
 For a parallel plate capacitor (two conducting
plates with a vacuum between the plates)
 Often, an insulator known as a dielectric is
placed between the plates to enhance
capacitance
• Dielectric constant: measures the strength of the
dielectric
C
A
d
=
ε 0

13. Capacitors and energy
 A charged capacitor stores an amount of
electric energy given by
• This energy can be thought of as stored in the electric
field between the plates.
U Q V=
1
2
2

14. Electric Current
 Electric current is defined as the amount
of charge that flows past a given point in
a second

15. Ohm’s Law
 Ohm’s Law related the resistance of an
object to the decrease in electric potential
across a point and the current flowing
through that point.
R
V
I
=

16. Electric Resistance
 Electric resistance is the innate ability of a
material to inhibit the passage of electrons.
• Measured in ohms.
• Given by the resistivity as well as the geometry of the
object.
R
L
A
= ρ

17. Circuits – emf and terminal
voltage
 A device that transforms one type of energy
into electrical energy is a “source of
electromotive force”
• emf: the potential difference between the terminals of a
battery when there is no current flowing to an external
source.
• A battery has some internal resistance
• The real voltage of a battery is then
V E I r= −

18. Resistors in series
 Voltage and
resistance are
additive
 Current is constant
everywhere in a
series circuit
R Re q i
i
= ∑
V Vt o t a l i
i
= ∑
I I It o t a l = = =1 2 . . .

19. Resistors in parallel
 Current additive
 Voltage is constant
everywhere in a
series circuit
 More resistors =
smaller equivalent
resistance
1 1
R Re q ii
= ∑I It o t a l i
i
= ∑
V V Vt o t a l = = =1 2 . . .

20. Complex Circuits

21. Kirchhoff’s rules
 Junction rule: At any junction point, the
total current into the junction has to be
equal to the total current out of the
junction.
 Loop rule: The sum of changes in
potential around and closed loop is zero.

22. Kirchhoff’s Rules

23. Magnetism
 Every magnet has two poles: north and
south
 Magnetic field & magnetic field lines:
analogous to electric field
• Direction: points north to south
 Electric current (moving charge)
produces a magnetic field!

24. Force due to magnetic fields
 The force on a charged particle moving through
a magnetic field
 The force in a current carrying wire immersed
in a magnetic field
F q v B= s i n θ
F I L B= s i n θ

25. Right hand rule

26. Ampere’s Law
 A moving charge (current) creates a magnetic
field.
• For a long wire, ∆l = 2πr
• Two wires can attract or repel due to this effect.
• A solenoid is a long coil of wire.
B l Ii
i
e n c l o s e d∆∑ = µ 0

27. Faraday’s Law
 A changing magnetic field induced an emf.
• A current produced by an induced emf moves in a
direction such that its magnetic field opposes the
original change in flux (Lenz’s Law)
• A coil rotating in a magnetic field is a good example
of this.
E N
t
= −
∆ Φ
∆