What are Dielectrics

• A dielectric is an insulating material in which all nuclei are tightly bound to the nuclei of the atom.
• There are no free electrons in a dielectric material so they can not carry current.
• Electric conductivity of a dielectric material is very low and that of an ideal dielectric is zero.
• Some examples of dielectric materials are glass, plastic, mica, oil etc.
• Dielectric constant of a material is the ratio of the capacitance of the capacitor completely filled with the material to the capacitance of the same capacitor in the vacuum i.e. dielectric constant K=C/C₀.
• If the space between a capacitor is filled with a dielectric material capacitance of the capacitor increases.
• The value of dielectric constant K is independent of the shape and size of the capacitor and its value is different for different insulating materials.

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Resonance Column Method and End Correction

This 2007 IIT JEE physics subjective practice problem requires the student to find the end correction, or difference between the frequency of a tuning fork and the corresponding sound waves inside of a tube, given the contextual information. This type of problem has an answer between 0 and 9999, with six points awarded for a correct answer. No points are subtracted for an incorrect response, so all problems in the subjective category may be attempted without penalty.
Problem
In the experiment for the determination of the speed of sound in air using the resonance column method, the length of the air column that resonates in the fundamental mode with a tuning fork is 0.30 m. When this length is changed to 1.00 m, the same tuning fork resonates with the first overtone. What is the end correction (in cm) for the column?
Solution
In the resonance column method, the pipe has one end closed and one end open. Let Δl be the end correction. Remember that the first resonance is, theoretically, one quarter of a wavelength, with the distance between resonances at half of a wavelength.
Thus, for the fundamental mode: 0.30 m + Δl = λ/4
For the first overtone: 1.00 m + Δl = 3λ/4
⇒ 3(0.30 m + Δl) = 1.00 m + Δl
⇒ Δl = 0.05 m = 5 cm.
Bio: Alexis Bonari is a freelance writer and blog junkie. She often can be found blogging about general education issues as well as information on college scholarships. In her spare time, she enjoys square-foot gardening, swimming, and avoiding her laptop.
Photo: Public Domain
URL: http://upload.wikimedia.org/wikipedia/commons/3/35/Kundt_tube.png