Solve Physics problem
A horizontal wire 10 cm long whose mass is 1 g to be supported magnetically against the force of gravity. The current in the wire is 10 A and goes from north to south, (a) What should be the direction of the magnetic field? (b) What should ist magnitude be?
To support the wire against gravity we should exert a force upwards on the wire against the weight. It is said that current flows from north to south. To find the direction magentic field, we can use Fleming's Left Hand Rule. If we keep thumb, index finger and middle finger of our left hand pointed in perpendicular direction to each other, middle finger indicated the direction of current and thumb indicated the movement and index finger indicated the direction of magnetic field.
So if we apply Fleming's rule here, we find that the direction of the magnetic field must be from west to east.
The weight of the wire `= 0.001 kg xx 9.81 ms^(-2) = 0.00981 N` .
The force exerted by the magnetic field can be calculated by the following equation,
`F = BLI sin(theta)`
Where `theta` is the angle between field and wire. In this case `theta` is 90 degrees so `sin(theta)` is 1. B is the magnetic flux while l is the length of rod or wire.
`0.00981 N = B xx 0.1 m xx 10 A xx 1`
`B = 0.00981 T.`
The magnitude of the magnetic field should be 9.81 mT in the direction of west to east.