Let us select a current element on circular loop `Ivecdl`. The magnetic field in radial direction will be perpendicular to current element vector. From left hand rule or right palm rule. we can find the direction of force `dvecF` on the element which comes to be perpendicular into the plane of the paper.
Required force `F=int dF=int idlB sin 90^@=int IdlB`
`=2piaiB` perpendicular to the plane.

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