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This algebra-based course covers basic concepts of physics including practical examples of the role of physics in other disciplines. The course is designed to develop physical intuition and problem-solving skills. Main keywords in this lecture are: Parallel-Plate Capacitor, Capacitance, Capacitor, K-Dielectric Constant, Isolated Charged Capacitor, Energy Stored in a Capacitor, Electric Current and Batteries, Batteries, Electric Current, Direct Current
Typology: Study notes
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Parallel-Plate Capacitor: Device used to store electrical potential energy and charge. It consists of two conducting sheets with equal and opposite charges. When the sheets are close to each other, the electric field inside is approximately uniform.
Capacitance
Capacitor: Two conducting surfaces separated by an insulating layer. It’s a device capable of storing charge and energy.
Capacitance=
potentialdifferencebetweenconductors
chargeonconductor plate
SI Unit: charge per volt=farad (F)
microfarad=F=10 -6^ F, picofarad=pF=10 -12^ F
Parallel plate capacitor with plate area A and separated by a distance d of dielectric material (insulator):
o
d
K-dielectric constant
2
12 2 o (^) N m ε 8.85x10 C
^ , permittivity of free space
o
d Cd K A
For air between conductor plates, K=
Add dielectric K results in capacitance C= K Co
Q=CV So, V =
(^) and E E K
For an isolated charged capacitor, the electric field and voltage difference decreases if a dielectric is placed between the plates. The charge on the plates remains unchanged.
For a capacitor connected to a battery, the voltage difference between the plates stays the same as a dielectric is placed between the plates, but the
charge increases: Q' Q K
Energy stored in a capacitor:
2 PE 1 Q V 1 C V^2 1 Q 2 2 2 C
Electric Current and Batteries
Batteries
Battery: Two electrodes (zinc and carbon) placed in electrolyte (dilute sulfuric acid).
Chemical reactions in electrolyte force positive charges to flow from negative zinc electrode to the positive carbon electrode.
Positive and negative battery terminals set up potential difference which forces positive charges in a circuit to flow along electric field direction (pos. to neg.)
Electric Current: flow of electric charges from one point to another-scalar quantity (charges + or -)
Electric Resistance, Ohm’s Law
Resistance: Interaction between flowing charges and atoms in electric circuit which resists (slows) current flow
R SI units: volt per ampere ≡ ohm (Ω)
Ohm’s Law: Relationship between the potential difference across an electric device and the current that runs through it.
V IR
Ohmic resistor: resistance stays constant as voltage (potential difference) over circuit element varies.
