The water molecule (shown below) has a net dipole moment p of magnitude 6.1 time
ID: 1533919 • Letter: T
Question
The water molecule (shown below) has a net dipole moment p of magnitude 6.1 times 10^-30 Cm, which can be considered as a vector sum of the two dipole moments p_1 and P-2 as shown. The H-0 distance is 0.96 angstroms and the angle the lines joining H-O-H make is 104 degree (a) Determine the effective charge q oil each H atom, (b) By adding the potential due to each dipole V_1 + V_2, show that the electric potential at large distances from the molecule is given by V = p cos theta/4 pi epsilon_0 r^2. Take V = 0 to be at infinity.Explanation / Answer
(a) The vector sum of the dipole moments is p = 2*q*d*cos(theta)
where, theta = the angle from the moments being parallel,
which is 52° in water.
Therefore P = 2*q*d*cos(52)
Given that p = 6.1*10^-30 C.m
d = 0.96*10^-10 m
Then 6.1*10^-30 = 2*(q*d)*cos(52)
q = 6.1*10^-30/(2*0.96*10^-10)*cos(52)
= 5.160*10^-20 C
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