Alternating Currents

Chapter 17 - Alternating Currents

This video describes the key conditions for a source to be considered an alternating one. In the GCE A Levels, sinusoidal sources are the most common type of alternating source.

One of the most important values in quantifying alternating sources is the root-mean-square or rms value. In the GCE A Levels, we understand the physical meaning of an rms voltage or rms current in terms of power dissipation, and we must also be able to compute the rms values for square wave alternating sources.

For the GCE A Levels, we have to be able derive and apply the root-mean-square values of sinusoidal sources. This video will run through this derivation and prove the quick formula for the rms values of sinusoidal sources.

This video describes the difference between peak and average power dissipation in the context of an alternating circuit. As required by the GCE A Levels, we will link peak and average power to peak and rms values of voltage and current, and show how these come together in a circuit involving a sinusoidal source.

The GCE A Levels requires us to understand the most basic form of AC to DC conversion, which is the process of half-wave rectification. This video explains how this is achieved with a diode.

In the GCE A Levels, we must know how to compute the root-mean-square (rms) values of voltage and current in a half-wave rectified sinusoidal circuit. This video will discuss the method to do this, and derive the formula for these rms values, and also for the average power dissipated in a half-wave rectified circuit.

Transformers are devices that can step-up or step-down an alternating voltage source. The GCE A Levels requires us to understand how a transformer is able to do this, and this video will show how the concepts of electromagnetic induction are strongly related to this ability.

This video explains what an ideal transformer is, and some of the mathematical relationships we can derive to help us analyse the functioning of an ideal transformer. For the GCE A Levels, we quantitatively deal with ideal transformers frequently, so we will understand the how the turns ratios are related to the primary and secondary voltages and currents.

In the GCE A Levels, we have to explain the various sources of power loss in a non-ideal transformer, including coil resistance, eddy currents and magnetic flux leakage. This video will also explain which formulae can be used for non-deal transformers, and briefly describes the process of lamination and its advantages.

In the GCE A Levels, we need to briefly understand one key application of transformers, which is in transmission lines. This video explains how stepping up the voltage before transmission helps to minimise the transmission current, and as a result minimise the power loss in the transmission lines.