Flashcards in Chapter 26 Deck (27):
What is Direct Current?
In Direct (DC) Current, the emf and currents are constant
eg) circuits involving batteries
What is Alternative Current?
In Alternative (AC) Current, the emf and current oscillate in time
eg) circuits involving a generator
What is AC Voltage?
The output of an AC Generator is sinusoidal and oscillates in time according to...
E = Eocos(2πft) = Eocos(2πt/T)
E - the instantaneous voltage at a given time
Eo = the maximum (or peak) voltage
T = is the period (the time for one full cycle)
f = 1/T = w/2π is the frequency (# of cycles/ time)
What are Resistors in AC circuits?
Kirchhoff's rules and Ohm's Law still hold in AC Circuits in AC Circuits:
v(R) = V(R)cos(2πft)
i(R) = v(R)/R = V(R)cos(2πft)/R = I(R) = cos(2πft)
What is the average Power dissipated by AC Circuits?
P(R) = (1/2)I^2R
What is Root Mean Square (RMS) Voltage and Current?
Irms = I(R)/√2 Vrms = V(R)/√2
What are Transformers?
An AC transformer consists of two coils of wire wound a core of soft iron
What is the Primary (N1) or (Np)?
the side connected to the input AC voltage source is called the PRIMARY and has N1 turns
What is the Secondary (N2) or (Ns)?
The other side, is called the secondary, is connected to a resistor and has N2 turns
What is the load?
The secondary is connect to a resistor called the load
What is a Step-Up transformer?
When N2>N1 the transformer is referred to as a Step-Up Transformer: it raises the voltage
When is a Step-Down transformer?
What are the formulas for a Step-Up and a Step-Down transformer?
What does is a Grounder?
Earth is a conductor, a circuit connected, to the earth is considered grounded
What is an Electrical Outlet?
Outlets are connected in parallel. Electricity provided by the power company is transmitted to outlets through wires in the walls
What is the neutral side of an electrical Outlet?
one terminal of the electricity supply is grounded, this is called the Neutral side
What is the Hot side of an Electrical Outlet?
the other side has varying potential, each outlet has two slots, one connected to each side
What is a Breaker?
A circuit breaker limits the current in each circuit. If an ammeter measures too much current, it sends a signal to open the switch to disconnect the circuit
What is a Ground Fault Interrupter?
outlets (GFI) have built in sensing circuit that compares the currents int he hot and neutral wires
- The current in these wires should be the same
What is an Induced Electric Field?
This means that there is an electric field, and induced electric field, pointing in the direction of the current
What induces and Electric Field?
a changing magnetic field induces, the an electric field, independently of any charges
- The induced electrical field produces a current, which produces a magnetic field
What are Electromagnetic Waves?
Electric and Magnetic fields play symmetric roles in nature
- If E and B change in just the right way there is a self-sustaining electromagnetic field
What induces a Magnetic field?
a changing electric field induces a magnetic field, independently of any wires or chargers
When ranking AC/LR circuits based on the current through the battery immediately after the switch is closed. What do you do?
You make the inducer, an "Open" as if it were an open space in the circuit or and open switch
When ranking Ac/LR circuits based on the current through the battery a very long time after the switch is closed. What do you do?
You make the inducer a "Short" imagine replacing the inductor with a bare wire
Inductance is Measured in what?
The symbol for Inductance is L
SI Unit is Henry's (H)