Question

An electret is similar to a magnet, but rather than being permanently magnetized, it has a permanent electric dipole moment. Suppose a small electret with electric dipole moment 1.0 × 10−7 Cm is 25 cm from a small ball charged to + 80 nC, with the ball on the axis of the electric dipole.

Answer 1

In this question, we need to find the magnitude of the electric force on the ball; the answer is
`9.21`
`*`
`10^(-3)`N.

Explanation:

To resolve this question, we're going to need E=
`(k(2p))/(r3 )` that is the magnitude of an electric field in the axis of a dipole at some distance "r" .

where "p" is the magnitude of the electric dipole moment, so in this case p= 1.0
`*`
`10^(-7)` Cm or what is the same
`10^(-7)`cm; and k is a constant k value is =
`k=8.99`
`*`
`10^(9)`
`(Nm2)/(C2)`

now to get the force on the ball we need to use F=qE where
`E=`
`(k(2p))/(r3 )`

so we have

`F= q*`
`(k(2p))/(r3 )`

for this, "q" is the charge on the ball, so we got 80nC or what si the same 80×
`10^(-9)`C, and r is the distance between the ball and the dipole, r= 25cm= 0.25m (1m=100cm, so we need to divide 25cm into 100 to get it in meters)

Replacing we got:

F=(80×
`10^(-9)`)(8.99×
`10^(9)`)(2(
`10^(-7)`)) /
`(0.25)^(3)`

and calculating this the answer is
`9.21`
`*`
`10^(-3)N`