Can someone explain what exactly a dielectric constant is? I know dielectric means insulator but I do not understand what exactly it is!!! All help is appreciated 🙂
dielectric constant
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It is relating how the electrical force is effected by different mediums as compared to that same electrical force in a vacuum. Check out the picture below:
Let's say that (a) is an electric field set up by parallel capacitor plates in a vacuum. A test charge placed in that electric field will feel force F according to the equation F=kq1q2/r^2.
Now, let's say that (b), (c), and (d) show that same electric field, but we have added water to it. Look at (b), (c), and (d) as if it were snapshots taken over time, where (b) = time 0. When you put water which is a polar substance into an electric field, the partial positive charge on water (hydrogens) will align with the negative plate of the capacitor. Conversely, the oxygen which has a partial negative charge will align itself with the positive plate of the capacitor. What this does is effectively lowers the force from F to F' felt by a test charge if it were placed in the medium because the partial charges on water are "shielding" the test charge from the applied electric field.
Since the dielectric constant is a ratio of force felt by a test charge in a vacuum to the force felt by a test charge in the medium, if the force felt in the medium is really small, the dielectric constant will be really big and vice versa.
Hope this explains it. Just a helpful tip when you get to capacitors: When you put a dielectric in a capacitor, you are lowering the force felt by a test charge in between a capacitor i.e. you are decreasing the voltage/electrical potential between the plates. Since Capacitance = Q/V, and Q remains the same while V decreases, the capacitance will increase. This is why placing a dielectric in between the plates of a capacitor will increase the capacitance.
Let's say that (a) is an electric field set up by parallel capacitor plates in a vacuum. A test charge placed in that electric field will feel force F according to the equation F=kq1q2/r^2.
Now, let's say that (b), (c), and (d) show that same electric field, but we have added water to it. Look at (b), (c), and (d) as if it were snapshots taken over time, where (b) = time 0. When you put water which is a polar substance into an electric field, the partial positive charge on water (hydrogens) will align with the negative plate of the capacitor. Conversely, the oxygen which has a partial negative charge will align itself with the positive plate of the capacitor. What this does is effectively lowers the force from F to F' felt by a test charge if it were placed in the medium because the partial charges on water are "shielding" the test charge from the applied electric field.
Since the dielectric constant is a ratio of force felt by a test charge in a vacuum to the force felt by a test charge in the medium, if the force felt in the medium is really small, the dielectric constant will be really big and vice versa.
Hope this explains it. Just a helpful tip when you get to capacitors: When you put a dielectric in a capacitor, you are lowering the force felt by a test charge in between a capacitor i.e. you are decreasing the voltage/electrical potential between the plates. Since Capacitance = Q/V, and Q remains the same while V decreases, the capacitance will increase. This is why placing a dielectric in between the plates of a capacitor will increase the capacitance.
Last edited:
It is relating how the electrical force is effected by different mediums as compared to that same electrical force in a vacuum. Check out the picture below:
Let's say that (a) is an electric field set up by parallel capacitor plates in a vacuum. A test charge placed in that electric field will feel force F according to the equation F=kq1q2/r^2.
Now, let's say that (b), (c), and (d) show that same electric field, but we have added water to it. Look at (b), (c), and (d) as if it were snapshots taken over time, where (b) = time 0. When you put water which is a polar substance into an electric field, the partial positive charge on water (hydrogens) will align with the negative plate of the capacitor. Conversely, the oxygen which has a partial negative charge will align itself with the positive plate of the capacitor. What this does is effectively lowers the force from F to F' felt by a test charge if it were placed in the medium because the partial charges on water are "shielding" the test charge from the applied electric field.
Since the dielectric constant is a ratio of force felt by a test charge in a vacuum to the force felt by a test charge in the medium, if the force felt in the medium is really small, the dielectric constant will be really big and vice versa.
Hope this explains it. Just a helpful tip when you get to capacitors: When you put a dielectric in a capacitor, you are lowering the force felt by a test charge in between a capacitor i.e. you are decreasing the voltage/electrical potential between the plates. Since Capacitance = Q/V, and Q remains the same while V decreases, the capacitance will increase. This is why placing a dielectric in between the plates of a capacitor will increase the capacitance.
Thanks so much! it actually makes a lot of sense now 🙂
