Question

I know it can be done using Right Hand Rule, but don't know how to solve it practically. Please help explain how to apply right-hand rule actually. Thanks!

A small charged particle of charge q7.0 x 10-6C and mass m - 3.1 x 10-12kg is accelerated through a potential difference of 19.6V before it enters a region of uniform magnetic field as shown by the rectangle in the following figure. The particle is observed to travel in the semicircular path of radius R 5.0 cm in the field. Region of magnetic field I Path of the Iparticle 1m (b) What is the direction of the magnetic field?

Answer 1

Here Direction of magnetic field will be into the page.

Hope this may help you -

(remember in our question, charge is negative- to understand it better- first apply the rule for positive charge and finally change the direction to get direction for negative charge. )

Physicists use a hand mnemonic known as the right-hand rule to help remember the direction of magnetic forces. To form the mnemonic, first make an L-shape with the thumb and first two fingers of your right hand. Then, point your middle finger perpendicular to your thumb and index finger, like this:

Image showing a hand in the right-hand-rule configuration

The right-hand rule is based on the underlying physics that relates magnetic fields and the forces that they exert on moving charges—it just represents an easy way for physicists to remember the directions that things are supposed to point. Occasionally a physicist will accidentally use their left hand, causing them to predict that the magnetic force will point in a direction opposite the true direction!

Moving charges

When charges are sitting still, they are unaffected by magnetic fields, but as soon as they start to move, the magnetic field pushes on them. But, the direction in which the field pushes on charges is not the same as the direction of the magnetic field lines. It instead looks more like this:

Image showing lorentz forces

We can remember this diagram using the right-hand rule. If you point your pointer finger in the direction the positive charge is moving, and then your middle finger in the direction of the magnetic field, your thumb points in the direction of the magnetic force pushing on the moving charge. When you’re dealing with negative charges—like moving electrons—the force points in the opposite direction as your thumb.