# Physics grade 12 3 identical charged particles in 3 corners of a triangle (read description)?

Need help studying before test, teacher was absent most of the week before the test and is terrible at explaining questions and is too fast for me to understand. Here's the question: Three identical charged particles sit at the corners of an equalateral triangle of side length 30cm (attached photo). Each particle has a charge of -8.5uC. Determine the magnitude and direction of the net force on each particle. Relevance

We know F = qE so the easiest way is to find the E field at one corner.  I will use the top corner.

The direction of the E field from the lower left charge at the top corner is 240°

The direction of the E field from the lower right charge at the top corner is 300°.

The distance squared = 0.3² = 0.09

The horizontal components are equal, opposite and cancel.

The vertical components are equal, both down and add.

Thus the E field at the top charge

= k*1e-6*8.5*(sin240+sin300)/0.09 = 1.47e6 V/m at 270°

The force on the top charge = qE = 8.5e-6*1.47e6 = 12.5N at 90°, opposite the field direction because the charge is negative.

The force on the lower left charge = qE = 8.5e-6*1.47e6 = 12.5N at 210°

The force on the lower right charge = qE = 8.5e-6*1.47e6 = 12.5N at 330°

This makes sense because like charges repel.

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