What Is the Force on a Charged Particle in a Magnetic Field?

AI Thread Summary
The discussion centers on calculating the force exerted on a charged particle moving in a magnetic field using the formula F = qv x B. A participant attempted to solve the problem using a determinant method but arrived at an incorrect direction for the force, believing it to be in the i direction instead of the -k direction as indicated in the textbook. Clarifications were requested regarding the correct application of the cross product, leading to the realization that the participant had made an error in their determinant calculation. The conversation highlights the importance of accurately setting up the determinant for vector cross products in physics problems. Ultimately, the participant corrected their mistake after receiving guidance on proper calculation methods.
bdh2991
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Homework Statement


a particle with a charge of -1.24 x 10^-8 c is moving with instantaneous velocity v= 4.19 x 10^4 i + -3.85 x 10^4 j (both in m/s). what is the force exerted on this particle by a magnetic field a) 1.4 T i and b) 1.4 T k ?



Homework Equations



F = qv x B (cross product not multiplication)



The Attempt at a Solution



I tried using a determinate for part a where you put i j k and the velocity vector multiplied by q and then the magnetic field vector underneath that but i got -6.68 x 10^-4 i, however the books answers says that it is in the -k direction.

I don't understand the way my physics teacher does the cross multiplication that's why i tried using a determinate like in calculus...please help??
 
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bdh2991 said:

Homework Statement


a particle with a charge of -1.24 x 10^-8 c is moving with instantaneous velocity v= 4.19 x 10^4 i + -3.85 x 10^4 j (both in m/s). what is the force exerted on this particle by a magnetic field a) 1.4 T i and b) 1.4 T k ?



Homework Equations



F = qv x B (cross product not multiplication)



The Attempt at a Solution



I tried using a determinate for part a where you put i j k and the velocity vector multiplied by q and then the magnetic field vector underneath that but i got -6.68 x 10^-4 i, however the books answers says that it is in the -k direction.

I don't understand the way my physics teacher does the cross multiplication that's why i tried using a determinate like in calculus...please help??
Can you show your work ?
 
SammyS said:
Can you show your work ?

sure, this is what i was trying to do: for part a)

i , j , k
q(4.19x10^4) , q(-3.85x10^4) , 0
1.4 , 0 , 0

(i added commas in-between to not confuse)

i did the cross product using this determinate thinking it would give me the right answer and i got the right number just the wrong direction...

q(-3.85x10^4)(1.4) in the i direction, the book says -k direction...
 
bdh2991 said:
sure, this is what i was trying to do: for part a)

i , j , k
q(4.19x10^4) , q(-3.85x10^4) , 0
1.4 , 0 , 0

(i added commas in-between to not confuse)

i did the cross product using this determinate thinking it would give me the right answer and i got the right number just the wrong direction...

q(-3.85x10^4)(1.4) in the i direction, the book says -k direction...
Use the code icon, https://www.physicsforums.com/Nexus/editor/code.png , to display items with lots of spaces, like your determinant ... or simply use [CODE ] [/CODE ] tags.

Code: 
i          ,                j            ,        k

q(4.19x10^4)  ,  q(-3.85x10^4)  ,    0

1.4           ,            0              ,     0

You are calculating your determinant incorrectly.

Show
what you multiply i by,
what you multiply j by,
what you multiply k by;​
including zeros, & prior to simplifying anything.
 
Last edited by a moderator:
I just figured out what i did wrong...i crossed out the columns and rows backwards...i didnt realize until you told me to write everything out lol thanks ...stupid mistake on my part
 
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