class 9 electricity
TRANSCRIPT
Electromechanical systemsElectromechanical systems
Class 9 – Electricity
Dr. Marisela Strocchia X [email protected] hours: Tuesdays from 11 to 1 pm
Fridays from 11 to 12 m
Agenda
• Next theory class on Tuesday 23 in room B212F from 12 to 3 pm
• Last class review:– Gas properties
• Electricity• Exercises• Homework
Last class review: Properties of Gases
What does happen when a gas is heated?When a gas is heated, the increased kinetic energy causes the volume
to increase, the pressure to increase, or bothCharles’ law– If the pressure on a gas is constant, the volume is directly proportional
to its absolute (Kelvin or Rankine) temperature V/T = V’/T’
Where: V = Original volume; T = Original temperature V’ = Final volume; T’ = Final temperature
Boyles’ law– If the temperature of a gas is constant, the volume is inversely
proportional to its absolute pressure V/ V’ = P’/P or VP = V’P’
Where: V = Original volume; P = Original pressure V’ = Final volume; P’ = Final pressure
• Boyles’ law experiment
Last class review: Properties of Gases
Density and PressureFrom Boyle’s law: V/ V’ = P’/P or VP = V’P’From density concepts D = m/V;
V = m/DV’ = m/D’
Substituting in Boyle’s lawm/D/ m/D’ = P’/P
D/D’ = P/P’
Where: V = Original volume; V’ = Final volume; P = Original pressure; P’ = Final pressure m = mass; D = Original density; D’ = Final density;
Last class review: Properties of Gases
Most of the time it is very difficult to keep the pressure constant or the temperature constant
Charles’ law and Boyles’ law combinedVP/T = V’P’/T’
Where: V = Original volume; T = Original temperature V’ = Final volume; T’ = Final temperature
P = Original pressure; P’ = Final pressure BOTH Pressure and Temperature MUST be absolute
Matter and electricity
Neutrons and protons are tightly packed in the nucleus, the electrons surround the nucleus. If an electron is removed, the atom is left with a + charge, that is an excess of protons. If an extra electron is added, the atom has a – charge, that is an excess of electronsMOVIE
The force F between two points charges q1 and q2 is directly proportional to the product of their magnitude and inversely proportional to the square of the distance separating them r 2
F= k q1 q2 /r
Where F = Force of attraction or repulsion (N) 9 2 2
K = 9x 10 Nm/C q1 and q2 = electric charges (C = Coulombs)
r = distance between the charges (m)
Coulomb’s law
The flow of charge in an electric circuit is often compared to the flow of water in a hydraulic system.
Ohm’s law
Series circuits
Series circuits
In a series circuit the emf or E (electromotive force, is "that which tends to cause current (actual electrons and ions) to flow.“ More formally, emf is the external work expended per unit of charge to produce an electric potential difference across two open-circuited terminals. The electric potential difference is created by separating positive and negative charges, thereby generating an electric field.)
Parallel circuits
A water system may be compared to a parallel electric circuit.
Parallel circuits
Parallel circuits
In a parallel circuit the emf or E (electromotive force, is "that which tends to cause current (actual electrons and ions) to flow.“)
Circuit A can be replaced by circuit B, where R4 is the equivalent resistance (R4 = R1 + R2). Then, circuit B can be replaced by circuit C, where R5 is the equivalent resistance (1/R5 = 1/R4 + 1/R3).
Compound circuits
Circuit A can be replaced by circuit B, where R4 is the equivalent resistance (1/R4 = 1/R2 + 1/R3). Then, circuit B can be replaced by circuit C, where R5 is the equivalent resistance (R5 = R4 + R1).
Compound circuits
Summary
• Problems: – 6 p 454– 5 p 468– 3 p 475– 5 p 479
Homework
• Ewen, Schurter and Gundersen (2009). Applied Physics. New Jersey: Prentice Hall
• Rex, A., Wolfson, R (2009). College Physics. Boston: Adison-Wesley
Bibliography