7.1 - Alternating Currents & Transformers Flashcards
What is the definition of an alternating current?
A current which periodically varies between a positive to a negative value with time.
What does A.C look like plotted on a graph?
Sinusoidal as the current varies every half cycle.
What is peak current/ peak voltage defined as?
The maximum value of the alternating current or voltage.
What is the rms value of an alternating current defined as?
The square root of the mean of the squares of all the values of the current in one cycle.
In an A.C circuit, how do electrons move in the current carrying wire?
They move back and forth with simple harmonic motion.
What is the rms of A.C equivalent to?
The direct current that produces the same power.
What is the equation to calculate the rms value of A.C?
Iᵣₘₛ = I₀/√ 2
I₀ = peak current
What is the definition of the rms value of an alternating voltage?
The square root of the mean of the squares of all the values of the voltage in one cycle.
What is the rms value of alternating voltage equivalent to?
The d.c voltage that produces the same power.
What is the equation to calculate the rms value of an alternating voltage?
Vᵣₘₛ = V₀/√ 2
V₀ = peak voltage
What is the rms value defined as?
The steady direct current, or voltage, that delivers the same average power in a resistor as the alternating current, or voltage.
How do you calculate the average power of a A.C circuit?
Average power = Iᵣₘₛ x Vᵣₘₛ
What are the applications of alternating current/voltage?
- Mains electricity is supplied as alternating current by the National Grid
What is the voltage and frequency produced by the mains electricity that goes into households?
- 230V (rms value)
- 50Hz
What does CRO stand for?
Cathode-Ray Oscilloscope.
What is a CRO used for?
It is a laboratory instrument used to display, measure and analyse waveforms of electrical circuits (can be used as an a.c and d.c voltmeter).
What is A.C voltage on an oscilloscope represented as? (what does it look like on the screen)
Transverse wave.
Since A.C voltage is displayed as a transverse wave on an oscilloscope, what can properties be measured?
- frequency, time period and peak voltage.
What is D.C voltage represented as on an oscilloscope? (what does it look like on the screen)
As a horizontal line at the relevant voltage.
Since D.C voltage is displayed as a horizontal line on an oscilloscope, what can properties be measured?
-x-axis is time, y-axis is voltage
- therefore voltage level is shown
What is the time-base on an CRO?
how many seconds each division represents.
(s/div, s/cm)
What happens when the time-base is turned off on a CRO for A.C?
Only a vertical line on the voltage-gain axis is seen with its relevant amplitude.
What does voltage-gain mean on an CRO?
The amount of voltage per division (per square).
What is a transformer
A device that changes high alternating voltage at low current to low alternating voltage at high current, (vice versa).