Q.

Consider a long thin conducting wire carrying a uniform current I. A particle having mass "M" and charge "q' is released at a distance "a" from the wire with a speed v0 along the direction of current in the wire. The particle gets attracted to the wire due to magnetic force. The particle turns round when it is at distance x from the wire. The value of x is [μ0 is vacuum permeability]          [2025]

1 a[1mv02qμ0I]    
2 a2  
3 a[1mvαqμ0I]  
4 ae4πmv0qμ0I  

Ans.

(4)

Let the velocity of the particle make an angle θ with initial direction when it is at a distance x.

 dxdt=v0 sin θ          ... (i)

Also, dθdt=qm(μ0I2πx)          ... (ii)

 dxdθ=2πmv0x sin θqμ0I          ... dividing eq (i) with eq (ii)

or axdxx=2πmv0qμ0I0πsin θdθ

lnxa=4πmv0qμ0I

Or x=ae4πmv0μ0Iq