In the picture above, the two wires carry current i 1 and i 2 , respectively, wi
ID: 1959448 • Letter: I
Question
In the picture above, the two wires carry current i1 and i2, respectively, with positive current to the right. The charge q is positive and has velocity v to the right. (true or false)
1) If i1 = 0 and i2 is greater than zero, then the force on q points out of the page.
2) If i1 = - i2, then the wires repel each other.
3) If i2 = 0 and i1 is greater than zero, then the magnetic field near charge q points out of the page.
4) If i2 = 0 and i1 is greater than zero, then the force on q is north.
5) If i1 is less than i2, then the force on q is south.
6) If i2 = - i1 then the force on q equals zero.
7) If v = 0, then the force on q is zero.
(please explain! thanks!)
Explanation / Answer
1) FALSE. the force on q points towards south. the direction of magnetic field at q by the wire is outside the page.( right hand thumb rule). also,direction of force on moving charge is perpendicular to the direction of the velocity of charge and the direction of magnetic field ( v X B ).
2) TRUE. The magnetic field around the wire carrying current -i2 by wire carrying i1 current is into the page. so taking direction of i2 as direction of arbitrary charge on that wire, the sign of force is directed away from wire i1( towards south), not towards it ( towards north). hence ther wires repel.
3)FALSE. the case is similar to case 1) , the diffence being that the magnetic field direction gets reversed. Here it is pointing into the page. So the force acting on charge is directed towards north.
4) TRUE.
5) TRUE. from cases 1) and 3) , we understand that individually the forces acting on the charge q by wire 1 and wire 2 are in opposite direction. so if i1< i2, the force will remain directed towards south, as in case 1), just its magnitude decreases.
6) FALSE. the force on q will be zero if i1=i2. then the two forces acting in opposite direction will cancel out each other. if i2=-i1, forces will add up and be directed towards north.
7) TRUE. only a moving charge experiences force by a magnetic field. stationary charges experiences no force. F= q.( v X B), if qis zero, F is zero.
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