Commutators

[Blakhitman]

Post your explanations here!

We all know it's gonna be on the paper tomorrow 

[superflya]

reverses the direction of current every half cycle to keep torque consistent. what else is needed, i can never fill up the 10 lines they provide on exams

[ghadz7]

reverses the direction of current every half cycle to keep torque consistent. what else is needed, i can never fill up the 10 lines they provide on exams

I always go beyond the 10 lines, although writing non-sense bull.

[Chavi]

From my cheat sheet:

•   Split ring commutator: Reverses the direction of the current every half turn. This reverses the direction of the forces on each side of the coil and therefore keeps the motor rotating in constant direction. It also stops the wire twisting when the coil rotates. Without it, the motor would eventually stop at 90 degrees.
•   Carbon Brushes – used to make contact between the split ring and the battery. Every ½ revolution – commentator changes connection with the other brush.
•   Purpose of a battery in a magnet/DC motor – to provide a p.d. and a current that produces a force on the coil, making it turn.


Although I've probably memorized these by now just by writing them heaps of times 

[schnappy]

•   Purpose of a battery in a magnet/DC motor – to provide a p.d. and a current that produces a force on the coil, making it turn.

Of all things, I think I can remember that...

[lachymm]

The current that will be induced will create a magnetic field that opposes the change in flux.

and

Electrons can only be stable if their orbit around the nucleus is a whole multiple of their wavelength. This creates a standing wave in which the electron is stable. Hence only discrete energy levels exist. This means that matter exhibits wavelike properties as forming a standing wave is a wave like phenomena

The reason why a transformer needs AC to work is because it operates by the primary coil producing a change in magnetic flux, current is only induced in the secondary coil if there is a constant changing magnetic field produced by the primary coil. DC is unable to bring about a continuous changing magnetic flux and hence transformers cannot work using a DC supply.

Can someone give me some good ones about the wave model and the particle theory about the photo electric effect? how it ultimately supports the particle model of light.

Cheers guys

[waack]

the only thing that supports a particle model only is the photoelectric effect, linear propagation, reflection etc can be explained by both

[Whatlol]

In the photo electric effect it was observed that incident light required a minimum frequency (or above) in order to produce the ejection of an electron. Futhermore increasing the frequency was seen to increase the energy of the ejected photoelectrons, and no appreciable time delay observed for emission of electrons. An increase in intensity produced an increase in the number of ejected photoelectrons.

 this conflicted the wave model approach which predicted increasing intensity would reduce the time delay and increase energy of the ejected photoelectrons, and that regardless of the lights frequency electrons will be ejected.

hope that helps

[Blakhitman]

Here's mine (I think I got it off VCAA report, can't remember):

A commutator changes the direction of the current in a DC motor every half rotation in order to keep it rotating in the same direction. If there was no commutator, then the motor would oscillate and eventually come to a stop.

[Blakhitman]

reverses the direction of current every half cycle to keep torque consistent. what else is needed, i can never fill up the 10 lines they provide on exams

I think maybe mention what would happen without it? To further emphasise it's use(fulness).