ch 26

Question 1

We often refer to the electricity at a typical household outlet as being 120 V. In fact, the voltage of this AC source varies; the 120 V is __________.

the minimum value of the voltage
the average value of the voltage
the peak value of the voltage
the rms value of the voltage

Answer 1

rms

Question 1

In a transformer, energy is carried from the primary coil to the secondary coil by

Answer 1

the magnetic field in the iron core

Question 2

A step-up transformer _____ the voltage and _____ the current.

Answer 2

raises;lowers

Question 3

If you plug two devices into the two plugs in a standard household outlet, the devices are connected __________.

Answer 3

in parallel

Question 4

A capacitor is connected to an AC supply. Increasing the frequency of the supply _________ the current through the capacitor.

Answer 4

increases

Question 5

An inductor and a resistor are connected in a simple series circuit. If the inductance increases, the current in the circuit

Answer 5

decreases

Question 6

An inductor is connected to an AC supply. Increasing the frequency of the supply _________ the current through the inductor.

Answer 6

decreases

Question 7

In an RLC circuit connected to an AC voltage source, which quantities determine the resonance frequency? Choose all that apply.

Answer 7

capacitance and inductance

Question 9

What is an Ac current defined by

Answer 9

An alternating emf that causes an alternating current

Question 10

What is a DC

Answer 10

It is a circuit with a steady emf and a current in the same direction always

Question 11

Because the AC circuit has a changing current and voltage, what is the current in a circuit element called

Answer 11

An instantaneous current

Question 12

How does the current direction change every half cycle in an AC CIRCUIT

Answer 12

It changes direction

Question 13

In an AC circuit, what is the relationship between the oscillations in current and voltage

Answer 13

They are in phase so the voltage will be at its max when the current is at its max

Question 14

For every cycle of emf, how does the instantaneous power relate

Answer 14

It oscillates twice for every cycle of emf

Question 15

For every cycle of emf, how does the instantaneous power relate

Answer 15

It oscillates twice for every cycle of emf

Question 16

What is the purpose of a transformer

Answer 16

It is a device that takes an AC voltage as an input and produces either a higher or lower AC voltage as its output

Question 17

What’s happening in the primary coil of a transformer

Answer 17

The AC voltage source creates an alternating current in the coil of wire. This creates an oscillating magnetic field that is transferred to the secondary coil by the iron core

Question 18

whats happening in the secondary coil of a transformer

Answer 18

the oscillating magnetic field from the primary causes a change in the flux in the secondary

this produces a induced voltage that creates a current that dissipates power in the load

Question 19

what is a step-up transformer

Answer 19

it is when N2>N1 and the voltage is increased

Question 20

what is a step down transformer

Answer 20

it is when N1<N2 and the voltage is decreased

Question 21

In a step up transformer, what happens to the current

Answer 21

it decreases

Question 22

in a step down tramsformer, what happens to the current

Answer 22

it increases

Question 23

what is the purpose of grounding

Answer 23

to provide a common reference point for potential difference

Question 24

what is the wire connected to the ground called? what is the side connected to the voltage?

Answer 24

neutral and grounded

Question 25

whats the purpose of a circuit breaker

Answer 25

when the amiplitude of a current exceeds a certain amount, the circuit breaker will switch open to disconnect the circuit

Question 26

what makes electric sources dangerous

Answer 26

not the voltage but the amount of current flowing through a body

Question 27

when do GFI circuits switch off

Answer 27

when they mesure a difference in current in the neutral and hot side, the current must be finding another way to the ground

Question 28

in a capacitor AC circuit, how are the voltage, charge, and current related

Answer 28

the voltage and charge are in phase, the current is out of phase

Question 29

in an AC circuit with a capacitor, does the current lead or lag the voltage

Answer 29

the current leads the voltage

Question 30

what is the capacitative reactance

Answer 30

it controls the rate at which a capacitor charges and discharges

Question 31

what happens to the reactive capacitance at high frequencies? At low frequencies?

Answer 31

at high frequencies the reactance decreases at low frequencies the capacitance increases

Question 32

when a current is increasing in a solenoid, what happens to the magnetic field and the induced emf

Answer 32

the magnetic flux increases and the induced emf will resist the change in the flux

Question 33

where does the direction of the potential difference in an inductor point

Answer 33

an inductor resists changes in the current through it

Question 34

when does an inductor develop a potential difference

Answer 34

it develops a potential difference if the current across it is changing

Question 35

what is an inductance

Answer 35

the property of an electric conductor or circuit that causes an electromotive force to be generated by a change in the current flowing.

Question 36

when is the voltage in an inductor high

Answer 36

when the current is rapidly changing

Question 37

when is the voltage in an inductor low

Answer 37

when the current is changing slowly

Question 38

does the AC current through an inductor lead or lag the inductor voltage

Answer 38

it lags the inductor voltage

Question 39

what is inductive reactance

Answer 39

it is the resistance an inductor offers to the AC current

Question 40

what is an LC circuit

Answer 40

A capacitor and an inductor

Question 41

what happens to the current and charge in an LC circuit

Answer 41

the current in an LC circuit doesn't stop, it continues until it has recharged the capacitor with the opposite polarization and it continues like this in an oscillation

Question 42

what is an RLC circuit

Answer 42

the current oscillates from the capacitor but energy is lost through a resistor as thermal energy

Question 43

what happens when we add an AC source to a RLC circuit

Answer 43

we create a driven RLC circuit

Question 44

what is the resonance frequency

Answer 44

it is the frequency at which the current is at its maximum value in an RLC circuit

Question 45

what happens to the emf of an inductor after some time has passed

Answer 45

Long after the switch is closed, the inductor generates no emf and acts like a wire with zero resistance.

Question 46

when a switch is first closed, what happens to the inductor

Answer 46

it acts as an open circuit, no current will flow

Question 47

when the switch is closed for a long time, what happens to the current

Answer 47

it gradually increases and then remains constant as there is no more change

Question 48

If you stuck a paperclip in each of the two slots of a GFI-protected outlet, then grabbed one paperclip with your right hand and the other paperclip with your left hand, would the GFI protect you?

Answer 48

t depends on whether you are grounded or not. If you are, the outlet is likely to register it through a difference in the currents and disconnect the circuit

Question 49

when does the inductor create a large emf

Answer 49

it is proportional to the rate of change in the current, so when the current is changing rapidly

Question 51

when is there a max current in an AC circuit

Answer 51

at the max change in voltage