# A level physics magnetic flux question

For part (i), use the right hand grip rule by positioning the turn of your fingers in the direction of current in coil. Your thumb will determine direction of magnetic field.
For (ii), we know that magnetic flux linkage can't be the same as it depends on the number of turns of coil. Magnetic flux density also can't be the same as it depends upon the radius of coil and we have been told that it is different for each coil. Hence magnetic flux would be the same, as only one coil has its own magnetic flux which is present throughout the ring. There is no change in f lux so no e.m.f induced the other coils.
For (iii), magnetic flux linkage would have the highest value for coil with 5 turns as it is proportional to number of turns OR magnetic flux would have highest value for the coil with 3 turns as it is present around the cross-section of wing with lowest radius, and magnetic flux is inversely proportional to radius of cross-section.
Original post by WordsFiddle
For part (i), use the right hand grip rule by positioning the turn of your fingers in the direction of current in coil. Your thumb will determine direction of magnetic field.
For (ii), we know that magnetic flux linkage can't be the same as it depends on the number of turns of coil. Magnetic flux density also can't be the same as it depends upon the radius of coil and we have been told that it is different for each coil. Hence magnetic flux would be the same, as only one coil has its own magnetic flux which is present throughout the ring. There is no change in f lux so no e.m.f induced the other coils.
For (iii), magnetic flux linkage would have the highest value for coil with 5 turns as it is proportional to number of turns OR magnetic flux would have highest value for the coil with 3 turns as it is present around the cross-section of wing with lowest radius, and magnetic flux is inversely proportional to radius of cross-section.

For (i), I got the current going to the right but how do i draw the lines going into the page?
For (ii) you mentioned flux density depends on radius, but how isn't is F/IL = B, also doesn't flux = BA depend on area (radius)?
For (iii) is there another equation for flux, as i thought it was BA?
Original post by efsfsf\\eeeeeee
For (i), I got the current going to the right but how do i draw the lines going into the page?
For (ii) you mentioned flux density depends on radius, but how isn't is F/IL = B, also doesn't flux = BA depend on area (radius)?
For (iii) is there another equation for flux, as i thought it was BA?

Sorry I got it wrong for (ii)....magnetic flux linkage also depends on radius you're right, magnetic flux density depends on the length of coil. Either way, I believe flux remains same.
For (i), I the direction of magnetic field is not into page, it is towards the left. Treat you fingers as the coil. The direction where the tip of your fingers point is the direction of current. Adjust your hand accordingly and then see where the thumb points.
For (iii), again I repeated the same mistake. It is flux linkage that depends on area of cross-section. However, magnetic flux density does have another equation in terms of permeability constant. You can google it. It also gives us an idea on what else flux is dependant on by substituting it. Generally, it is BA.
Sorry for the mistakes again 🙂 I confused length of coil with radius of cross-section.
(edited 1 month ago)
Original post by WordsFiddle
Sorry I got it wrong for (ii)....magnetic flux linkage also depends on radius you're right, magnetic flux density depends on the length of coil. Either way, I believe flux remains same.
For (i), I the direction of magnetic field is not into page, it is towards the left. Treat you fingers as the coil. The direction where the tip of your fingers point is the direction of current. Adjust your hand accordingly and then see where the thumb points.
For (iii), again I repeated the same mistake. It is flux linkage that depends on area of cross-section. However, magnetic flux density does have another equation in terms of permeability constant. You can google it. It also gives us an idea on what else flux is dependant on by substituting it. Generally, it is BA.
Sorry for the mistakes again 🙂 I confused length of coil with radius of cross-section.

No problem, i still don't get the flux though, does the cell mean that there's only flux in the 3 turn coil due to emf and if so wouldnt that mean no flux in the others?
Original post by efsfsf\\eeeeeee
No problem, i still don't get the flux though, does the cell mean that there's only flux in the 3 turn coil due to emf and if so wouldnt that mean no flux in the others?

Well the iron core would concentrate the flux within itself so that the flux of coil with 3 turns passes through the other coils.
Flux will only be there if current is present. There is no current in the other coils, and there won't be any Induced current either as there is no change in flux.
Original post by WordsFiddle
Sorry I got it wrong for (ii)....magnetic flux linkage also depends on radius you're right, magnetic flux density depends on the length of coil. Either way, I believe flux remains same.
For (i), I the direction of magnetic field is not into page, it is towards the left. Treat you fingers as the coil. The direction where the tip of your fingers point is the direction of current. Adjust your hand accordingly and then see where the thumb points.
For (iii), again I repeated the same mistake. It is flux linkage that depends on area of cross-section. However, magnetic flux density does have another equation in terms of permeability constant. You can google it. It also gives us an idea on what else flux is dependant on by substituting it. Generally, it is BA.
Sorry for the mistakes again 🙂 I confused length of coil with radius of cross-section.

Hey there, for part (i), I get the current curling with your fingers as the coil wraps around the iron ring which also gives me the current going to the left, but could you please describe how to draw the complete lines of magnetic flux on the diagram? Would you just draw 2 lines going to the left? The mark scheme says "two closed loops linking primary coil - lines not touching/crossing, both passing only through iron core" but I'm still unsure. I'm a little rusty on this topic, it's been a while unfortunately
Original post by 4wzy
Hey there, for part (i), I get the current curling with your fingers as the coil wraps around the iron ring which also gives me the current going to the left, but could you please describe how to draw the complete lines of magnetic flux on the diagram? Would you just draw 2 lines going to the left? The mark scheme says "two closed loops linking primary coil - lines not touching/crossing, both passing only through iron core" but I'm still unsure. I'm a little rusty on this topic, it's been a while unfortunately

Hi. The lines will be a full loop inside the ring. As the cross section increases, the seperation of the lines will increase.
(edited 1 month ago)