Reactance and impedance — practice questions

Question 1 · difficulty L1 · recall

Inductive reactance is

• A. XL=1/(ωL)
• B. XL=ωC
• C. XL=ωL
• D. XL=R/ω

Question 2 · difficulty L1 · understanding

Capacitive reactance is

• A. XC=ωC
• B. XC=ωL
• C. XC=Rω
• D. XC=1/(ωC)

Question 3 · difficulty L2 · understanding

The SI unit of reactance is

• A. ohm
• B. henry
• C. farad
• D. tesla

Question 4 · difficulty L2 · application

As AC frequency increases, inductive reactance

• A. decreases
• B. increases
• C. remains constant
• D. becomes negative resistance

Question 5 · difficulty L3 · application

As AC frequency increases, capacitive reactance

• A. increases
• B. remains constant
• C. decreases
• D. becomes equal to capacitance

Question 6 · difficulty L3 · application

For a series RLC circuit, impedance magnitude is

• A. R+XL+XC
• B. sqrt(R²+XL²+XC²) always
• C. XL-XC without R
• D. sqrt(R²+(XL-XC)²)

Question 7 · difficulty L4 · analysis

A pure inductor is connected to AC. Current relative to voltage

• A. lags by 90°
• B. leads by 90°
• C. is always in phase
• D. lags by 180°

Question 8 · difficulty L4 · analysis

A pure capacitor is connected to AC. Current relative to voltage

• A. lags by 90°
• B. leads by 90°
• C. is in phase
• D. lags by 180°

Question 9 · difficulty L5 · analysis

In a series RLC circuit, XL=30 Ω, XC=10 Ω and R=20 Ω. The impedance magnitude is

• A. 60 Ω
• B. 20 Ω
• C. 20sqrt(2) Ω
• D. 40 Ω

Question 10 · difficulty L5 · analysis

At very low frequency, an ideal capacitor in series tends to behave as

• A. a short circuit with zero reactance
• B. a pure inductor
• C. a negative resistor
• D. a very large reactance