Physics122
Exam #2
November 6, 2013
12:00 to 12:50 pm
Constants and equations for exam 2. You may detach this page if you wish.
Coulumb’s Law constant
k=8.99 x109 N m2/C2
Permittivity of free space
ε0=8.85 x10-12 C2/N m2
Charge of one electron
-e=-1.60 x10-19 C
Magnetic permeability of free space
µ0=4π x10-7 T m /A
________________________________________________________________________________
Electric current
Definition: I=ΔQ/Δt
V=IR – Ohms law
Power: P=IV
In a resistor: P=I2R=V2/R
Resistance and resistivity: R=ρl/A
Resistors in DC circuits
Series connection:
Parallel connection:
1
1
1
1
Req=R1+R2+R3
=
+
+
Req R1 R2 R3
V=V1+V2+V3
V=V1=V2=V3
I=I1=I2=I3
I=I1+I2+I3
Kirchhoff’s rules
Junction rule (charge conservation): At any junction point the sum of all current entering the
junction must equal the sum of all currents leaving the junction
-Assign initial signs based on your best guess – if you were wrong the currents will turn to be
negative (opposite to initial guess)
Loop rule (energy conservation): The sum of the changes in potential around any closed path of a
circuit must be zero
-For resistor Vab=-IR – negative if the current is along the loop direction, positive otherwise,
-For battery Vab – positive if the loop direction is from – to + , negative otherwise
_______________________________________________________________________________
Magnetic field
µ I
Ø B = 0 – magnetic field created by electric current, 1st right hand rule: thumb long the
2π r
current – fingers show the magnetic field
  
Ø F = BIl sin θ ; F = Il × B magnetic force on electric current, 2nd right hand rule: fingers
along the current, bend in the direction of the magnetic field, thumb shows the force.
Ø F=qvB sin θ – magnetic force on moving charged particle in magnetic field
a=v2/r – centripetal acceleration
Ø B=KB µ In – magnetic field in solenoid, n=N/l
 
Ø ∫ Bdl = µ0 I encl - Ampere’s law
 
 µ 0 I dl × rˆ
Ø dB =
- Biot-Savart law.
4π r 2
________________________________________________________________________________
Trigonometry review
sin θ = (opp) /(hyp), cosθ = (adj) /(hyp), tan θ = (opp) /(adj)
Pythagorean theorem: (hyp) 2 = (opp) 2 + (adj) 2
0
5