Most challenging part of Unit 3 Physics?

[Alevine]

Hey everyone!
Unit 3 Physics for most schools is drawing to a close now, and some of you might have even started Unit 4 already in class.

Now that you've been exposed to all the content from Unit 3 (and survived the SAC's, experiments, tests, etc.), what do you think the hardest part of physics from Unit 3 actually were?

For me, when I first started, I think Special Relativity was the most conceptually challenging thing to learn (simultaneity in S.R was a killer).

Was this hardest for you guys as well? What did you guys find the most challenging?

[zhen]

I struggle with anything that has finding the direction of something in electromagnetism. Like using the right hand slap rule in a SAC can get really fidgety and I'm still not sure what I do when I have a circuit. Do I reverse the right hand slap rule because of negatively charged electrons, or do I not because of conventional current.

[Syndicate]

I struggle with anything that has finding the direction of something in electromagnetism. Like using the right hand slap rule in a SAC can get really fidgety and I'm still not sure what I do when I have a circuit. Do I reverse the right hand slap rule because of negatively charged electrons, or do I not because of conventional current.

(I am not Alevine, and I hope no minds me answering)

Yes. Your thumb, from your right hand , points in the direction of the conventional current (the direction in which positive charges are moving). If an electron is travelling to the right, then your thumb should be pointing to the left, and vice versa. You roll your hand around a wire to determine from which side the current is going into the page (represented by and X), and out of the page (represented by a bold dot- make sure your dot is large enough to be seen).


Take this image for example. The direction of I represents the flow of conventional current, hence the thumb must be pointing upwards. From our perspective, using the right hand slap rule, current is coming out of the page from left, and going into the page from the right. Therefore you have to draw bold dots on the left, and Xs on the right. It should look something like:

* * * | x x x
* * * | x x x (where * represents a dot)
* * * | x x x

Note: The thumb pointing towards the direction of the conventional current also applies to the right hand rule for solenoids and the right hand slap rule to determine the direction of the magnetic force.