# Find i j k force on charge

1. Oct 1, 2009

### inconceivable

1. Find in the i, j, k format, the force on the +8 micro-Coulomb charge (pic att'd)

F = 1.6 x 10^-4 N

no clue where to start

thx

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• ###### dipole.jpg
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Last edited: Oct 1, 2009
2. Oct 1, 2009

### Delphi51

Use the formula for electric field causing a force on a charge: Fe = q*E

3. Oct 1, 2009

### inconceivable

got that. that's where the 1.6 x 10^-4 came from.

4. Oct 1, 2009

### Delphi51

Are you finished then, or do you need to add the electric field due to the other charge? A good idea to show formula and numbers - the answer is not much of a clue as to what you have done.

5. Oct 2, 2009

### inconceivable

electric field strength is on the image - 20 N/C

the issue here is, they want it in i, j k format

6. Oct 2, 2009

### Delphi51

Okay.
1.6 x 10^-4 * cos(60) i + 1.6 x 10^-4 * sin(60) j + 0k

7. Oct 2, 2009

### inconceivable

thanks delphi. can you explain the cos and sin portion a bit? i never really could understand why those are used to express a single side of a triangle

8. Oct 2, 2009

### Delphi51

Expressing a vector as a horizontal part plus a vertical part makes it very convenient to add vectors (just add the h and v parts separately without worrying about angles). Also, in something like a trajectory problem the motion in two perpendicular directions is independent, so you can do the horizontal part of the problem without worrying about the vertical part.