Alternating Current Flashcards
What does an AC source do?
It creates an electrical current that varies in magnitude and direction periodically with time as opposed to direct current source where the direction of the current stays constant
What is the formula for the mean power dissipated?
Pmean = (Irms)^2R
What is the definition of the rms value of current and volatge?
It is the value of a steady direct current (or volatage) that would produce the same average power in a given resistor.
What is the rms and power dissipated in a sinusoidal ac supply?
Take the mean square voltage to be half of the square.
how is the mean power dissipated related to the peak power dissipated?
The mean power dissipated is HALF of the peak poewr dissipated
What is the formula for Irms/ Vrms?
I rms = I0/sqrt(2)
V rms = V0/sqrt(2)
What is the function of a transformer?
It is to convert one alternating voltage to another alternating voltage of a different magnitude.
What is the ratio of the current and voltage in the primary and secondary coils of a transformer?
Current -> reciprocal
Voltage -> same ratio
i.e Ns/Np = Ip/Is
Ns/Np = Vs/Vp
What is the formula to calculate power loss when transmitting from generator to electrical installations?
P = I^2R
^ can only use this as P = V^2/R can only be used if you know the PD across the wires.
What is meant by rectification?
Rectification is the process of converting an alternating current or voltage source into direct current or voltage supply.
Why is an AC source required to transmit electrical energy? (in the context of power stations)
An AC current will cause a change in magnetic flux, which induces an emf and allows for the step up or step down of voltage.
Explain why the voltage is stepped up near the power plant.
The step up of voltage lowers the current and since the power loss across the wires to the transformers near the houses is given by the formula P = I^2R, the lower the current, the lower the power loss.
(in the context of charging a phone)
Explain why a 3.7V ac supply takes a longer time to charge a 3.6V battery as compared to a 3.7V dc supply.
For a 3.7V ac supply, the voltage can sometimes be more or less than 3.6V, in fact for most of the time, the voltage is below 3.6V and therefore does not charge the battery, and is in fact discharging it. As compared to the 3.7V dc supply, where the voltage supplied is a constant 3.7V and will constantly be charging therefore take less time to charge.
What does it mean when the “emf is 3.6V”?
It means that 3.6 joules of energy is converted to other forms of energy for every 1 coulomb of charge that passes through the battery.
