The earth's magnetic field varies from point to point in space. Does it also change with time? If so, on what time scale does it change appreciably?

A magnetic field that varies in magnitude from point to point but has a constant direction (east to west) is set up in a chamber. A charged particle enters the chamber and travels undeflected along a straight path with constant speed. What can you say about the initial velocity of the particle?

What is the value of magnetic field at any point in the open space inside a toroid?

What are magnetic field lines ? How is the direction of a magnetic field at a point determined ?

When light travels from air to glass, the property which does not change is