magnetic field lines can be entirely confined within the core of a toroid but not within a straight solenoid. Why?

Please explain me first the meaning of the question and then the answer

 a torroid is a circular solenoid.

magnetic field is generated due to current flowing in the torroid and solenoid. In a torroid it is concentreted only within the core while in a  solenoid it is like that of a bar magnet

the reason for this is that in torroid everywhere except the core, the magnetic field due to individual wire turns cancel out.

in solenoid, magnetic field due to individual wire turns cancel longitudinally but they add up horizontally. so, magnetic field exists even outside the core.

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If the fields lines were entirely confined between two ends of a straight sloenoid, the Flux through the cross section at each end would non zero. But the flexor field B through any closed surface must always be zero(integration B. ds=0).For toroid this difficultly is absent as it has no ends.
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toroid is closely wound solenoid with a large no. of turns
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because it's nature of nature
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Because solenoid have end & starting points but toroid don't have
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The magnetic field outside the toroid (ideal one) is zero . That's not the case with solenoid . Magnetic field , unlike electric fields , has to end up where it starts , or in other words , they should form circular loops . In a solenoid (even if it extends infinitely ) , there is some amount of magnetic field outside , but very weak . 
That's where toroid kind of wins in containing a field inside it . Inside toroid , the magnetic field forms a perfect loop (no field leaking).
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