Alternating Current

Question 1

What is the approximate frequency of mains electricity?

Answer 1

50Hz

Question 2

What is the equation linking Voltage at a specific time to the source voltage (amplitude)?

Answer 2

V(t)=V0*sin(2πft)

Question 3

What is the angular frequency?

Answer 3

2π/Time period

Question 4

What is it called when there is a time discrepancy between two waves?

Answer 4

Phase Lag or Phase Shift, Φ

Question 5

What is impedance?

Answer 5

The complex resistance of a component which causes phase shift to alternating signals as well as decreasing amplitude

Question 6

For a component of impedance Z=a+bj, how are the amplitude reduction and phase shift of an AC signal determined?

Answer 6

Amplitude^2=a^2+b^2

Phase Shift = arctan(b/a)

Question 7

What is the impedance of a capacitor?

Answer 7

-j/ωC

Question 8

What is the impedance of an inductor?

Answer 8

jωL

Question 9

What happens to capacitors and inductors with DC flow?

Answer 9

Capacitor: Charge is stored up until no more current can flow
Inductor: Short circuit is created as the rate of change of current = 0

Question 10

How do you multiply impedance in phaser form?

Answer 10

Multiply coefficients and add angles

Question 11

What is the ratio of output to input voltage in a low pass filter?

Answer 11

Vo/Vi = Zc/(Zc+Zr)

Question 12

How do you convert voltage ratios to dB?

Answer 12

20log(Vo/Vi)

Question 13

What is the dB value when the angular frequency equals the characteristic frequency?

Answer 13

-3

Question 14

How is a high pass filter different to a low pass?

Answer 14

Capacitor and resistor are flipped

Equation uses 1/j ωRC instead of j ωRC