A cross product is 1) Something I know about. 2) Something Ive heard - - PowerPoint PPT Presentation

A cross product is

1) Something I know about. 2) Something I’ve heard about but I can’t remember what it is. 3) Something I’ve never heard about.

Figure 27.4a

Magnetic Field (B)

• Produced by “magnets”
• Compass Needle points parallel to the magnetic field

Electric Force: Magnetic Force:

E

q  F E  

B

q   F v B   

Products between vectors

• Scalar (or Dot) Product

– The result of this product is a scalar (number).

• Vector (or Cross) Product

– The result of this product is another vector. – Direction: – Magnitude:

cos c    A B A B     

  C A B   

is perpendicular to both and . C A B    sin  C A B   

Vectors that go in or out

• Vector/Arrow pointing at you – you see the

sharp tip.

• Vector/Arrow pointing away from you – you

see the feathers on the tail.

Which way does the cross-product vector point?

• Right-hand rule (#1)

– Use your right hand! – Point fingers in direction of – Move fingers towards – Thumb points in direction of – Corollary: A 

B 

  C A B   

    B A A B    

The particle in the figure 1) is positively charged. 2) is negatively charged. 3) could be negatively or positively charged.

If the magnetic field vector is directed toward the north and a positively charged particle is moving toward the east, what is the direction of the magnetic force on the particle?

1) up 2) west 3) south 4) down 5) east

A positively charged particle is moving northward in a magnetic field. The magnetic force on the particle is toward the northeast. What is the direction of the magnetic field?

1) up 2) northeast 3) southwest 4) down 5) This situation cannot exist.

Figure 27.17