Question

According to the Biot-Savart Force Law and the right hand rule, if a magnetic field is directed rightward (+ x axis) and a positive test charge moves through the field downwards (- y axis), which direction will the magnetic force be applied onto the charge?
1. upwards (+ y axis)
2. leftward (- x axis)
3. out of the screen (+z axis)
4. into the screen (- z axis)

Answer 1

Answer:

3. out of the screen (+z axis)

Explanation:

As we know that magnetic force on a positive moving charge is given by

$\vec F = q(\vec v \times \vec B)$

here we know that

$\vec B$ = Towards right (+X)

$\vec v$ = downwards (-Y)

charge is given as positive charge

now as per above formula we have

$\vec F = q(v (-\hat j) \times B \hat i)$

$\vec F = qvB \hat k$

so the force will be out of the screen (+Z) direction

Answer 2

The direction would go upwards(+yaxis)