Lesson test: Reactance, impedance and resonance

1.[2p]
The reactance of a capacitor, $X_{C} = 1 / (ω C)$ ,

falls as frequency rises, so a capacitor passes high frequencies more easily

Correct

rises as frequency rises

The answer is: falls as frequency rises, so a capacitor passes high frequencies more easily

does not depend on frequency

The answer is: falls as frequency rises, so a capacitor passes high frequencies more easily

is measured in farads

The answer is: falls as frequency rises, so a capacitor passes high frequencies more easily

2.[2p]
Unlike a resistor, a pure capacitor or inductor consumes no average power because

it stores energy for part of the cycle and returns it in the next, rather than dissipating it

Correct

it has no reactance

The answer is: it stores energy for part of the cycle and returns it in the next, rather than dissipating it

it blocks all current

The answer is: it stores energy for part of the cycle and returns it in the next, rather than dissipating it

it converts all energy to heat

The answer is: it stores energy for part of the cycle and returns it in the next, rather than dissipating it

3.[2p]
A 100 millihenry inductor is in a 50 Hz circuit ( $ω = 314$ rad/s). What is its reactance, in ohms? Give it to the nearest whole number.

CorrectNot quite: 31

4.[3p]
Resistance and reactance combine into impedance by the right-angle rule $Z = \sqrt{R^{2} + X^{2}}$ because

resistance acts in step with the current while reactance acts a quarter cycle away

Correct

they are always equal

The answer is: resistance acts in step with the current while reactance acts a quarter cycle away

reactance is negative

The answer is: resistance acts in step with the current while reactance acts a quarter cycle away

impedance is their simple sum

The answer is: resistance acts in step with the current while reactance acts a quarter cycle away

5.[2p]
Resonance occurs at the frequency where

the inductive and capacitive reactances are equal and cancel

Correct

the resistance is largest

The answer is: the inductive and capacitive reactances are equal and cancel

the capacitor is fully charged

The answer is: the inductive and capacitive reactances are equal and cancel

the frequency is zero

The answer is: the inductive and capacitive reactances are equal and cancel

6.[3p]
A circuit has a 100 microhenry inductor and a 100 picofarad capacitor. What is its resonant angular frequency, in radians per second? Use $ω = 1 / \sqrt{L C}$ .

CorrectNot quite: 10000000

7.[2p]
A radio tunes to one station because a resonant circuit

responds hugely at its resonant frequency and weakly at all others, so it picks out one and ignores the rest

Correct

amplifies every station equally

The answer is: responds hugely at its resonant frequency and weakly at all others, so it picks out one and ignores the rest

blocks all frequencies

The answer is: responds hugely at its resonant frequency and weakly at all others, so it picks out one and ignores the rest

converts radio waves to heat

The answer is: responds hugely at its resonant frequency and weakly at all others, so it picks out one and ignores the rest

1.[2p] The reactance of a capacitor, XC=1/(ωC),

2.[2p] Unlike a resistor, a pure capacitor or inductor consumes no average power because

3.[2p] A 100 millihenry inductor is in a 50 Hz circuit (ω=314 rad/s). What is its reactance, in ohms? Give it to the nearest whole number.

4.[3p] Resistance and reactance combine into impedance by the right-angle rule Z=R2+X2 because

5.[2p] Resonance occurs at the frequency where

6.[3p] A circuit has a 100 microhenry inductor and a 100 picofarad capacitor. What is its resonant angular frequency, in radians per second? Use ω=1/LC.

7.[2p] A radio tunes to one station because a resonant circuit

1.[2p]
The reactance of a capacitor, $X_{C} = 1 / (ω C)$ ,

2.[2p]
Unlike a resistor, a pure capacitor or inductor consumes no average power because

3.[2p]
A 100 millihenry inductor is in a 50 Hz circuit ( $ω = 314$ rad/s). What is its reactance, in ohms? Give it to the nearest whole number.

4.[3p]
Resistance and reactance combine into impedance by the right-angle rule $Z = \sqrt{R^{2} + X^{2}}$ because

5.[2p]
Resonance occurs at the frequency where

6.[3p]
A circuit has a 100 microhenry inductor and a 100 picofarad capacitor. What is its resonant angular frequency, in radians per second? Use $ω = 1 / \sqrt{L C}$ .

7.[2p]
A radio tunes to one station because a resonant circuit