1. Introduction: A look at calendar- Walk-in Lab 1; What is it? Where do you find the lab sheets? Where is the lab?_____ When are they due? The Teaching Associate will visit the walk-in lab, when?

Help sections?
 

2. Review of qualitative aspects of static electricity

How to produce a dipole using electrical induction
 

3. Quantitative aspects: (See SG 3-4) or Ex 23-2 of text. Approaching vector force law: 3 charges in a line.
 

4. EX3 Superposition: We mean by superposition that the total force is the vectorial sum of all the individual forces
 

How do you write the Electric force Law in vector form?

5. What is a Vector?

How do we write a vector in cartesian form?
 

What is i hat?
 

What does (1,2,0) mean? Write it in terms of unit vectors:

What is its length?

What is r hat? It is given by: r hat = r/r.
 

6. Electrical Force Law

If we write the Electric force Law in vector form as F=k_eq₁q₂r/r³ is it a 1/r³ law?

How do you write the Electric Field Law in vector form?
 

7. Electrical Field See 4-6 on sheet 2. Faraday was an nonmathematical genius. It we say that a value for the air temperature can be assigned to each point in space in a room then we say that there is a s_______ field in the room. So what does it mean that there is an electrical field around a charge distribution?

Is it a scalar or a Vector field?

[We will also use MU to capture concept of field]
 

8. Math review exam (see sample review in packet): Vector part: know dot and cross product, length of vector and angle between vectors,

Vector Math Review Style Problems from Serway, components- 53-75,

dot [or scalar] product. Description is on page 174-76, Sample problems: chapt.7: 12-21.

cross [or vector] product. Description is on page 309-311:

Sample problems; chapt. 11: 7-14. These are all in volume 1, copies in tutorial lab.

HW set B 1 & 2 Hints:

P10 : q = 2 x10^-6C.

P24: 1.8 x 10⁴ i -2.2 x10⁵ j N/C, or 2.2 x 10⁵N/C at -85^o from the positive x-axis.
 

1.There are point charges,q at (0,-1,2), (1,2,0) and (-2,0,-1) what is the force a charge, -q, fields at the origin?
 
 
 
 
 
 
 
 
 
 
 

2. What is the y-component of the cross product of [2,-2,1] and [3,4,1]?

a. determinant = i j k (see Serway vol. 1, Chpt 11: pp 310-311:)

2 -2 1 (Sample HW problems are on page 327.also see Web page.)

3 4 1

b. Other facts: i x j = k =-j x i j x k = - k x j = i

k x i = - i x k = j
 

A x B = 3i + 4j + k

x[2i - 2j + k]
 

= [6ixi + 8ixj + 2ixk] + [(-2)(3)jxi + (-2)(4)jxj + (-2)(1)jxk] +

[(1)(3)kxi + (1)(4)kxj + (1)(1)kxk]= - 6i +[3 -2]j + [8-(-6)]k

= -6i + j + 14k
 

3. What is the angle between the vectors [2,-2,1] and [3,4,1]?

Should we use the cross product or dot (scalar) product? Clue: NEVER USE CROSS PRODUCT for ANGLES!!!
 

dot product D = AB = A_xB_x + A_yB_y + A_zB_z = (2)(3)+

(-2)(4) +(1)(1)=-1 (see Serway vol. 1, Chpt 7: pp 175-76 and 194-5)*
 

mag A=sqrt(AA) =(A_xA_x + A_yA_y + A_zA_z)

=[A_x²+ A_y²+ A_z²] =[2²+2²+1²]^½= 3
 

mag B=sqrt(BB)=(B_xB_x + B_yB_y + B_zB_z)

=[B_x²+ B_y²+ B_z²] =[3²+4²+1²]^½= 5.1
 

cos = D/AB =-1/[3x5.1] =-0.0654

= arccos(D/AB) =arccos(-0.0654)=93.7º

____________________________________________________
 

CROSS PRODUCT?: mag(AxB) = (mag A)(mag B)sin

Sin=mag(AxB)/(magA)(magB)={[(-6)²+1²+14²]^½=[233]^½}/[ 3x5.1] = 0.998

= arcsin[ 0.998] = 86.3º {ACCORDING TO YOUR CALCULATOR.}

SO WHICH ONE IS RIGHT? DOT PRODUCT: 93.7º. CROSS PRODUCT CAN'T GET ANGLES BETWEEN 90º AND 180º.

*You can find Serway cross product problems at http://128.187.18.10/~allred/s310.gif 9 also s311.gif and s327.gif. Dot or scalar products are at http://128.187.18.10/~allred/s175.gif, s176.gif, and s195.gif, Solns to odd numbered problems are at back of the 122 book (Serway, Vol. 2) .