HSC Physics Question Thread

[winstondarmawan]

Hi,
Confused with whether the radial magnetic field will allow for increased change in flux or none at all? So whether the current output increases or not?

Thanks.

Gonna bump this because I am interested in the answer too

[jamonwindeyer]

Gonna bump this because I am interested in the answer too

The radial field will probably not increase the maximum level of current you get from the generator, but it will remove the sinusoidal variation in that current. You'll have a (relatively) constant output because the rate of change of flux will be constant! It MAY be greater, but no way to know for sure and not what that question would be targeting

So great to see everyone being so helpful in this thread! Seriously incredible! I'll be around to help tonight if anything still has people stumped 🏼

[Aaron12038488]

how likely will hsc assessments (excluding exams) like practicals and take home assessments, will be a repeat from each year?

[blasonduo]

how likely will hsc assessments (excluding exams) like practicals and take home assessments, will be a repeat from each year?

Coming from my school, they are NORMALLY the same thing every year, I remember in year 7 around term 2 a bunch of home made generators would pop up on the back bench and here I am, sitting at my desk with the generator above me.

Older years have also told me the similarity in assignments each year, with maybe a question tweaked here and there.

This is my school, and I don't know how other schools do it, but it just seems easier for teachers to give out the same assignment every year

[f_tan]

When doing calculations to find GPE, do you include the negative?
Thanks!

[kiwiberry]

When doing calculations to find GPE, do you include the negative?
Thanks!

Yes always!! Unless they ask for the magnitude of energy

[left right gn]

Hello,
Can we someone please explain the graphs in motors and generators. Such as EMF, flux, voltage output.
I'm confused on all the graphs of all these, please help!

[yattmoani]

Hello! I've been doing some questions of BOSTES and I came across these questions. Help would be greatly appreciated

[jamonwindeyer]

Hello,
Can we someone please explain the graphs in motors and generators. Such as EMF, flux, voltage output.
I'm confused on all the graphs of all these, please help!

Hey! So these graphs are representations of some pretty important concepts - Electromagnetic induction, back EMF, Lenz's Law, etc etc. To understand the graphs you need to understand those concepts, there's no set pattern unfortunately! I've written some nice succinct guides on Motors and Generators, they are linked in the middle of this resource list. Perhaps they would be helpful?

If there are any specific examples of graph questions you are confused about, upload em! Happy to help

[jamonwindeyer]

Hello! I've been doing some questions of BOSTES and I came across these questions. Help would be greatly appreciated

Hey! For the first one, we know a current will flow, and since the relative motion of the disc and the magnetic field is always the same, it will be a direct current, so we can cut out two answers straight away! By the right hand slap rule, the current induced will move towards Brush Y (remember fingers in direction of field, thumb in direction of movement, slap in direction of current  - So I'm fairly sure the answer C?

Second one, we know the induced emf will be a maximum when the coil is parallel to the field, so we need to start at a peak value. There is one full rotation, so one complete oscillation. This matches Graph B!

This is a really tough one to explain online, but it again relies on right hand grip rule. Remember first that the force on a charged particle due to movement in a magnetic field is perpendicular to both the field AND the movement. So if we want it to experience a force in the same direction as current, it can't be moving in that direction initially. So that rules out A and B.

So if current goes upwards (let's say), that means the field will be into or out of the page around it. To get a force in the same direction as the current, we need it to be moving towards it to get an upwards force. In honesty, I'm thinking of ways to explain this, but I really can't without being there next to you showing it to you in real time, aha. Try it - Try the right hand slap rule and see what happens when the electron is moving towards the wire - It should all line up to give you a force in the same direction as the current

[yattmoani]

Oh my bad I forgot to add the answers to each of the questions. The answer for the first question according to BOSTES is actually B?

[12carpim]

Hey,
This is a multiple choice question from a SBHS trial and i need some help in identifing the answer to the question 

[pikachu975]

Hey,
This is a multiple choice question from a SBHS trial and i need some help in identifing the answer to the question 

I think D since generators don't have back emf only motors.

[jamonwindeyer]

Hey,
This is a multiple choice question from a SBHS trial and i need some help in identifing the answer to the question 

That's a really dodgy question. Back EMF in motors is just the name given to the induced emf due to the rotation of the coil in the field. In a generator, that induced emf is the output voltage we want in the first place. The use of the terminology isn't appropriate here in my opinion

Assuming it just means induced emf, the answer is B. Induced emf is proportional to rate of change of flux, and the second graph matches that - It is a maximum when flux is changing the most

[kiwiberry]

Oh my bad I forgot to add the answers to each of the questions. The answer for the first question according to BOSTES is actually B?

The current generated with induce a magnetic field which opposes the original field, so using the right hand palm rule (fingers pointing left, palm towards direction of movement) current will flow downwards from Y. Therefore current flows from Y to X through the globe