Moon:

MCAT Physics Mini-Tutorial: Capacitors & Dialectrics

6 months ago
Moon:

6 months ago
Moon:

$${\bf{Capacitors:}}$$ - for the MCAT you will mostly be concerned with parallel-plate capacitors which are typically two metal plates connected to a voltage source and separated by some distance - capacitance: Q/V basically, stored charge/voltage - units are the Farad but are often given as microFarads since 1 Farad is a very large amount - for parallel plate capacitors: C = ε_0 * (A/d) where ε_0 is the permittivity of free space (given on the constants sheet), A is the area of the capacitor surface, and d is the distance between them - capacitors also produce a uniform electric field given by E = V/d with the field lines pointing from the positive plate to the negative plate - capacitors also store potential energy U = (1/2)CV^2

6 months ago
Moon:

$${\bf{Dialectrics:}}$$ - dialectric material: an insulating material placed between the plates of a capacitor to increase the capacitance - increases by a factor κ (kappa). new capacitance = κ * old capacitance - isolated capacitors (aka not connected to a circuit): dialecctric decreases the voltage while charge stays the same - circuit capacitors: dialectric increases the stored charge while voltage stays the same - the energy from a capcitor can discharge across the plates or by adding a conductive material

6 months ago
Moon:

$${\bf{Capacitor~Calculations:}}$$ - for capacitors in series: 1/total capacitance = sum of 1/C for each capacitor - for capacitors in parallel: total capacitance = sum of all capacitances note: this rule is the opposite of the rules for resistors |dw:1531616827062:dw|

6 months ago
Moon:

Anyway, that's the end of my tutorial, I hope it was a helpful resource. Source material is the Third Edition Kaplan Physics & Mathematics Prep Book for the new MCAT

6 months ago