Chapter 26

Question 1

What is Direct Current?

Answer 1

In Direct (DC) Current, the emf and currents are constant
eg) circuits involving batteries

Question 2

What is Alternative Current?

Answer 2

In Alternative (AC) Current, the emf and current oscillate in time
eg) circuits involving a generator

Question 3

What is AC Voltage?

Answer 3

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)

Question 4

What are Resistors in AC circuits?

Answer 4

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)

Question 5

What is the average Power dissipated by AC Circuits?

Answer 5

P(R) = (1/2)I^2R

Question 6

What is Root Mean Square (RMS) Voltage and Current?

Answer 6

Irms = I(R)/√2 Vrms = V(R)/√2

Question 7

What are Transformers?

Answer 7

An AC transformer consists of two coils of wire wound a core of soft iron

Question 8

What is the Primary (N1) or (Np)?

Answer 8

the side connected to the input AC voltage source is called the PRIMARY and has N1 turns

Question 9

What is the Secondary (N2) or (Ns)?

Answer 9

The other side, is called the secondary, is connected to a resistor and has N2 turns

Question 10

What is the load?

Answer 10

The secondary is connect to a resistor called the load

Question 11

What is a Step-Up transformer?

Answer 11

When N2>N1 the transformer is referred to as a Step-Up Transformer: it raises the voltage

Question 12

When is a Step-Down transformer?

Answer 12

When N2

Question 13

What are the formulas for a Step-Up and a Step-Down transformer?

Answer 13

V2=(N2/N1)V1 V2(rms)=(N2/N1)V1

I2=(N1/N2)I1 I2(rms)=(N1/N2)I1(rms)

Question 14

What does is a Grounder?

Answer 14

Earth is a conductor, a circuit connected, to the earth is considered grounded

Question 15

What is an Electrical Outlet?

Answer 15

Outlets are connected in parallel. Electricity provided by the power company is transmitted to outlets through wires in the walls

Question 16

What is the neutral side of an electrical Outlet?

Answer 16

one terminal of the electricity supply is grounded, this is called the Neutral side

Question 17

What is the Hot side of an Electrical Outlet?

Answer 17

the other side has varying potential, each outlet has two slots, one connected to each side

Question 18

What is a Breaker?

Answer 18

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

Question 19

What is a Ground Fault Interrupter?

Answer 19

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

Question 20

What is an Induced Electric Field?

Answer 20

This means that there is an electric field, and induced electric field, pointing in the direction of the current

Question 21

What induces and Electric Field?

Answer 21

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

Question 22

What are Electromagnetic Waves?

Answer 22

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

Question 23

What induces a Magnetic field?

Answer 23

a changing electric field induces a magnetic field, independently of any wires or chargers

Question 24

When ranking AC/LR circuits based on the current through the battery immediately after the switch is closed. What do you do?

Answer 24

You make the inducer, an “Open” as if it were an open space in the circuit or and open switch

Question 25

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?

Answer 25

You make the inducer a “Short” imagine replacing the inductor with a bare wire

Question 26

Inductance is Measured in what?

Answer 26

The symbol for Inductance is L

SI Unit is Henry’s (H)

Question 27

What is the formula that relates Potential Difference to Inductance?

Answer 27

V = LΔI/Δt 
ΔI = change in Current (A)
Δt = change in time (s)
L = Inductance (H)
V = Potential Difference/Voltage (V or Emf)