Chapter 17 2 Capacitance By Diego Hernandez Diego

Chapter 17 -2 Capacitance By: Diego Hernandez, Diego Ayala, and Dilpreet Kahlon. 1 of 9 © Boardworks Ltd 2009

Formula Chart Formula Name Capacitance for a Parallel. Plate Capacitor in a Vacuum Electrical Potential Energy Stored in a Capacitor 2 of 9 Equation Explanation Capacitance is equal to the charge on each plate divided by the potential difference. Capacitance is equal to the permittivity of a vacuum multiplied to the quotient of the area of one of the plates and the distance between the plates. Electrical Potential Energy is equal to PEelectric = half of the product of the charge on (½)(Q)(∆V) one plate and the final potential difference. © Boardworks Ltd 2009

Chart Measurement Name Definition Capacitance C Electric Potential V 3 of 9 Units SI Unit The ability of a conductor to store energy in the form of electrically separated charges F F How energetic charges are V V © Boardworks Ltd 2009

Capacitance explained Capacitance is the ability of any body to store an electrical charge. Any material that can be made to hold a charge experiences capacitance. Charges may be placed on these materials by static electricity or by an electric current. “Capacitor” is another name for these kinds of objects that are charged by electrical currents. As charge is added to a capacitor, the potential energy inside of the capacitor increases. Capacitors tend to (Circuit board symbol) 4 of 9 look like this: © Boardworks Ltd 2009

Capacitance cont. The capacitance of a capacitor depends on two things, its charge (Q), and change in potential difference (V). Normally, a large charge will produce a smaller potential difference, and thus, a larger capacitance. Reversely, a small charge produces a bigger potential difference, and a smaller capacitance. Capacitance is measure in Farads (F), though normally you will find that the capacitance is in microfarads (µF) because of the small sizes of capacitors on a circuit board. 5 of 9 © Boardworks Ltd 2009

Electric Potential and Permittivity Electric Potential is the amount of work it takes to move a charge from one of the capacitor’s parallel plates, to the other. Once a charge moves to another plate, a small potential difference is created between the two plates. As the next charges flow through this potential difference, the electrical potential energy of the entire system increases. 6 of 9 © Boardworks Ltd 2009

Practice 17 B #1, a A 4. 00 µF capacitor to a 12. 0 V battery. What is the charge on each plate of the capacitor 2 C = 4. 00µF 1 ∆V = 12. 0 V 3 Q = 4 (C x ∆V) 5 6 7 of 9 Q = (4. 00 x 10 -6 F)(12. 0 V) = 4. 80 x 10 -5 C © Boardworks Ltd 2009

Practice 17 B #1, b If the same capacitor is connected to a 1. 50 V battery, how much electrical potential 1 energy is stored? (refer to previous example) 2 C = 4. 00µF ∆V = 1. 5 V 3 PEelectric = 4 (½)(C)(∆V)2 5 6 8 of 9 PEelectric = (½)(4. 00 x 10 -6 F)(1. 5 V)2 = 4. 5 x 10 -6 J © Boardworks Ltd 2009

Quiz 1. What is capacitance? A. Capacitance is the ability of any body to store an electrical charge. 2. What is the value of the permittivity constant? A. 8. 85 x 10 -12 2 C /Nm 2 3. What is electric potential? A. Electric Potential is the amount of work it takes to move a charge from one of the capacitor’s parallel plates, to the other 9 of 9 © Boardworks Ltd 2009