In the picture below, the 3 charges Q 1 , Q 2 and Q 3 are located at positions (

Question

In the picture below, the 3 charges Q1, Q2 and Q3 are located at positions (-a,0), (a,0) and (0,-d) respectively. (The origin is the point halfway between Q1 and Q2.)

a) Select true or false for each statement.

1.The external work done to bring these charges to this configuration (from infinity) was positive.
2.The work required to move Q3 from its present position to the origin is zero.
3.The electric potential at the origin equals Q3/(40d).

(Here k = 1/(40))

4.The force on Q3 due to the other two charges is zero.
5.The electric potential at any point along the y-axis is positive.
6.If Q3 is released from rest, it will initially accelerate to the right.
7. The electric field at the origin points in the positive y direction.

Explanation / Answer

a . true , the force x component on the Q3 due to Q2 is to the right , the force x component due to Q1 is to the right , so the Q3 will accelerate to the right , b.True , since Q2 = -Q1 ,potential due to them cancels ;we are left with only Q3 , c . false , had the force been zero , the chagre would not accelerate to the right as shown in a , d . false , since the field due to Q! is to the right , the field due to Q2 is to the right , field due to Q3 is along y direction , obviously the vector sum of these cant point in y direction , e ,true at any point along y axis , the potential due to Q2 and Q1 cancels becasue that point remains equidiastant from Q1 and Q2 , and Q1 = - Q2 ; The V = k Q / r ; f .true the potential at the present positons is 0 , the potential at the fina l positon is also zero , becuse it is at equla distance from Q1 and Q2 , and Q1 = - Q2 ; W = 0 ; g . false no work was done to bring the third charge , negtive work was done to bring the poisitve and negative charges

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