Unstable equilibrium in case of dipoles

In summary, the stability of a dipole in an electric field depends on the angle it makes with the field. When the angle is zero or 180 degrees, the dipole is in equilibrium and will return to its original position after a small displacement. This is because the torque of the electric forces will rotate the dipole back to the equilibrium position. However, when the angle is any other value, the dipole is in unstable equilibrium and will be rotated away from the equilibrium position. This is due to the fact that the torque is not zero in this case. The stability can be visualized through a free body diagram, where the forces on the dipole are shown. In the case of a dipole in an electric field, the
  • #1
gracy
2,486
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I know in case of unstable equilibrium of dipoles when dipole makes zero angle with electric field intensity ,But how we decide that this is unstable equilibrium I know in case of unstable equilibrium dipole returns to it's place after the small displacement ,I want to know why or how?why/how does it return to it's original position after the small displacement ?
 
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  • #2
gracy said:
in case of unstable equilibrium of dipoles when dipole makes zero angle with electric field vector
Shouldn't the dipole be in equilibrium when it makes zero angle with the E field?
 
  • #3
gracy said:
in case of unstable equilibrium of dipoles when dipole makes zero angle with electric field intensity
I meant 180 degrees
 
  • #4
When the angle is 180 degrees, the dipole will also be in equilibrium position. Free body diagram can explain all this.
 
  • #5
main question is
gracy said:
,I want to know why or how?why/how does it return to it's original position after the small displacement ?
 
  • #6
See these pictures, red is positive and blue is negative. After all, the system of a dipole in a uniform monodirection electric field is the same as a pendulum under gravitational field.
 

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  • #7
gracy said:
I know in case of unstable equilibrium of dipoles when dipole makes zero angle with electric field intensity ,But how we decide that this is unstable equilibrium I know in case of unstable equilibrium dipole returns to it's place after the small displacement ,I want to know why or how?why/how does it return to it's original position after the small displacement ?
In the first case (stable), if you rotate it a little bit from equilibrium the torque of the electric forces will rotate the dipole back to the zero angle.
In the second case (unstable) the torque will rotate it away from equilibrium.
The torque is zero for both cases (zero and 180) but but is not zero if the angle is changed a little bit.
 
  • #8
nasu said:
the torque will rotate it away from equilibrium.
nasu said:
torque of the electric forces will rotate the dipole back to the zero angle.
Why?That's my main concern!
 
  • #9
Why what? Why there are electric forces or why they rotate this way?
If it's the second part. just look at the force diagrams in the two cases.
 
  • #10
nasu said:
just look at the force diagrams in the two cases.
I am not able to grasp the diagrams.
 
  • #11
I want to know why Dipole tend to restore it's original position when displaced a little from 0 degree (with Electric field)but the dipole does not do the same(does not restore it's position)when displaced a little from 180 degree (with Electric field)
Want to understand with the help of force diagram but I am not getting those in post #6 because I want to take dipole as a whole not positive and negative charges
 
  • #12
gracy said:
I want to know why Dipole tend to restore it's original position when displaced a little from 0 degree (with Electric field)but the dipole does not do the same(does not restore it's position)when displaced a little from 180 degree (with Electric field)
Actually I have given you a very straightforward hint: pendulum under gravitation. Are you familiar with such mechanical system? In term of energy, it's a matter of which energy state is more favorable for this system to be in. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/diptor.html
gracy said:
Want to understand with the help of force diagram but I am not getting those in post #6 because I want to take dipole as a whole not positive and negative charges
Easy. Just move those force arrow lines to the complete dipole picture.
 
  • #13
gracy said:
I am not able to grasp the diagrams.
I don't mean the diagrams posted here.
Just draw the forces on each charge, from the external field. The forces between the charges are not relevant. In order to have a stable dipole these forces are already balanced by some sort of repulsive forces.
Imagine a rigid stick with forces applied to the ends and see which way will rotate.
The forces are along the vertical direction, either up or down, depending of the sign of the charges.
 

1. What is unstable equilibrium in case of dipoles?

Unstable equilibrium in case of dipoles refers to a state where the dipole is in a position of balance, but any slight disturbance can cause it to shift and become unbalanced. This is because the dipole is in a position where the forces acting on it are not in equilibrium, resulting in an unstable state.

2. How does unstable equilibrium affect dipoles?

Unstable equilibrium can affect dipoles by making them less stable and more prone to movement. This can result in changes in their orientation or alignment, as well as potential disruptions to their interactions with other particles or fields.

3. What factors contribute to unstable equilibrium in case of dipoles?

Several factors can contribute to unstable equilibrium in case of dipoles, including the strength and direction of the dipole's electric field, the presence of other dipoles or charged particles, and external forces such as gravity or applied electric fields.

4. How can unstable equilibrium in case of dipoles be observed or measured?

Unstable equilibrium in case of dipoles can be observed or measured through various techniques, such as using polarized light to visualize changes in the dipole's orientation, or measuring the strength of the dipole's electric field with sensitive instruments.

5. Can unstable equilibrium in case of dipoles be controlled or stabilized?

In some cases, unstable equilibrium in case of dipoles can be controlled or stabilized through external forces or by manipulating the properties of the dipoles themselves. However, it is important to note that this may not always be possible and can depend on the specific conditions and characteristics of the dipoles in question.

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