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Homework Statement
A charge Q is fixed at the centre of a train track, radius R. An electric dipole with charges Q, -Q, separated by distance d. Show that the net force on the dipole is given by F = Q2d/(4πε0R3)
b) What direction is this force?
c) What is the torque on the dipole?
Homework Equations
F = (1/4*π*ε0) * (Qq/R2)
F = qE+-qE-
The Attempt at a Solution
sinθ = d/2R
F = (Q*Q / 4*π*ε0R2) (d/2R) - (-Q*Q / 4*π*ε0R2) (d/2R)
F = (Q2 d / 8*π*ε0R3) + (Q2 d / 8*π*ε0R3)
F = (2*Q2 d / 8*π*ε0R3)
F = Q2 d / (4*π*ε0R3)
b) The direction of the force is in the counter-clockwise direction (CCW). The charge on the left side of the dipole is repulsive, so it points away from the charge in the middle, while the charge on the right side is attractive, so it points towards the charge. The net force is then pointed towards the left.
c) I'm a bit lost with c) and I'm not really sure where to start. Any guidance would be much appreciated. :)
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