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### Course: AP®︎/College Physics 2>Unit 5

Lesson 4: Magnetic flux and Faraday's law

# Faraday's Law for generating electricity

How Faraday's Law is used to generate electricity in turbines.

## Want to join the conversation?

• Can anyone explain me about the sinusoidal behaviour of the induced emf in an ac generator?
I am unable to understand why the emf curve goes below the x-axis as the armature coil rotates. E.M.F is on y-axis and direction of magnetic field is on x-axis.
• Do we have an exact formula to count the change in flux if we rotate the loop? Thx.
• If I get your question right, you need to work out the 'rate of change of area' as the loop turns. Is this what u mean?
• why does the direction of current in generator change. And what would happen If instead of slip rings we used split rings?
• Hello Harshulsurana,

The direction of current is a function of the relative motion of the conductor and the magnetic field. You can visualize this using the right hand rule.

Slip rings give us an AC machine.

A commutator (split rings) give us a DC machine

Regards,

APD
• Is the triangle symbol a greek letter?
(1 vote)
• Yes. Δ is the Greek capital letter "Delta". When it appears before any variable, it means "change in ...". So in this video, for example, there is Δt, and that means "change in time". You always calculate the change by subtracting the initial value from the final value, so Δt = tf - ti
• i cant understand why the electromagnetic curve goes below the x axis as the armature coil rotates. electromagnetic is on y-axis and direction of the magnetic field is on x axis
• what are the avantages of having AC current? Or do we usualle try to convert this into DC?
• A really short answer would be that it´s more energy efficient and easier to generate, and the process for transforming AC is really easy(not so the other way around).For really know the reasons of this , you have to go deeper in electronics. :)
• Can some one explain in detail the differences between AC and DC. I mean I know that one displays sinusoidal behaviour and can travel over longer distances without getting disturbed but can someone explain the why and how of that or direct me somewhere where I can learn about that .

Thanks for the help !
• Hello VIshnu,

Here I explain DC and AC as mathematical function and give examples of where each type of power is found in an electrical power system. It also introduces the technology that allows you to convert between the two types.

At some point in the future I hope to do a video on DC transmission where you will see that DC is king for long distance transmission.

Regards,

APD
• When rotating the loop Sal says that the component of the Magnetic Field is going to increase, How?
• At the picture on the left shows a loop of wire turning in a constant magnetic field. As the loop rotates the number of flux lines enclosed within the loop changes. This change in flux induces a voltage in the loop.
Keep spinning! APD
• where's the limit of increasing number of loops to augment the motor strength?
• Increasing the number of loops increases the EMF of the coil. Increasing the EMF of the coil will increase the amount of energy needed to make it spin. Windmills are designed to work efficiently, with coils and magnets matched to where the windmill will reach peak power output, but not to where it exceeds peak power output. The wings on windmills should only spin so fast as to not exceed the maximum current allowed through the system, limitations of the system could include its electrical wiring and components, also it's mechanical and structural components. So, the limit of loops really comes down to the specific generator, although there may be a theoretical limit based on magnet size. Approaching that limit would more than likely require too much energy to rotate at any speed to produce current.
• If the turn ratio of a transformer is 10. What does it mean?

Turns ratio is literally a ratio. Recall that a transformer is composed of two coils of wire. Each coil consists of some number of "turns" around the transformer's core.

Suppose a transformer that has a turns ratio of 1 to 10. Let the first coil consist of 500 loop of wire. The second coil will have 5000 turns.

This turns ratio is very important as it also describes the voltage into and out of the transformer. In this example if the input voltage is 100 VAC the output voltage is 1000 VAC.