AC CIRCUIT Flashcards
Why cant we use ohms law in AC circuits
Because current and voltage can be out of phase with each other
What device changes DC to AC?
rectifiers
What does a transformer do in AC circuits?
It changes the voltage in AC circuits
What are instantaneous values?
They are values of alternating quantities of any instant of time/ they are values that change with time
What is the peak to peak value?
The difference between the maximum and minimum values of a cycle
What is the mains supply in the UK?
240V / 240 RMS
What does the phase shift mean?
Phase shift is when the current and voltage are out of step with each other.
Why do we say that the current leads the voltage in AC circuits?
Charging and discharging occur continually in AC circuits, and the current reaches its maximum before voltage does which is why we say it leads the voltage
What are some phaser properties?
. The length of a phaser is proportional to the maximum value of the alternating quantity involved
. The projection of a phasor on the vertical axis gives the instantaneous value of the alternating quantity involved.
What is the opposite to current flow?
Resistance
Why do we say voltage and current are in phase with each other in PURE AC circuits?
Because resistance is independent of frequency
How much does the current lag in PURELY INDUCTIVE AC circuits?
The current lags the applied voltage by 90 degrees, e.g. pi/2 radians
What is the opposition to the flow of alternating current called?
Inductive reactance
What is reactance used to calculate?
Amplitude and phase changes of sin alternating current
What happens to reactance as frequency increases?
Inductive reactance increases and capacitive reactance decreases
What reactance does an ideal resistor have?
Zero
What resistance do ideal inductors and capacitors have?
Zero
What is inductive reactance directly proportional to?
The supply frequency because the back EMF is dependant upon the rate of change of current
In PURE AC circuits by how much does the current lead the voltage?
The current leads the applied voltage by 90 degrees, e.g. pi/2 radians
What is the relationship between inductive and capacitive reactance called?
CIVIL
Because in a capacitor (C) the current (I) is ahead of the voltage (V) which is ahead of the current (I) for the inductor (L)
