Question

proton is actually an "ionised hydrogen atom". what does it mean? what is meant by "ionisation"?

Answer 1

ionization of hydrogen means that hydrogen gives its electron to some other atom or in strong radiation where radiation kicks his electron out... so in short ionization is taking of electrons in hydrogen case one electron...

Answer 2

Thanx
What is Electron to Charge ratio (e/m)? What is it used for?

Answer 3

it is used in variety of situations and cases of which are some famous: cathode tubes, particle accelerators, mass spectroscopy and so forth
it states that particles with same e/m ratio move in vacuum in same electric field on the same path or radius with same speed...

Answer 4

What might be puzzling you is that an ionized hydrogen atom is the same thing as a proton. The reason is that the hydrogen atom is very simple: it's just one proton with one electron orbiting it. If you take away the electron -- which is what "ionization" does -- then all that's left is the proton.

All other atoms have more than one proton and more than one electron, so if we take away one electron, we're still left with a nucleus containing more than one proton, and at least one orbiting electron. We call this an ionized atom, but it is not, unlike hydrogen, just one particle.

With respect to your second question: the charge-to-mass ratio of the electron (e/m) is just what it sounds like: the charge on the electron divided by its mass. Why is it useful? Because all particles with the same charge-to-mass ratio will move identically in the presence of electric and magnetic fields. It's the same sense in which the mass itself is useful when you think about motion in a gravitational field, e.g. when you think about balls being thrown up and falling down: all objects with the same mass will move identically in a gravitational field. You don't need to know the shape, size, et cetera of the object.

The reason the charge-to-mass ratio is key for electric and magnetic fields is because the force on a charge, moving or not, is given by F = q (E + v x B), which combines Coulumb's Law and the Lorentz Law for moving charges. Here F is the force, q is the charge, v is the velocity, and E and B are the electric and magnetic fields. (Note some of these quantities are vectors.) You can see the force is proportional to the charge.

Now, the response of the particle to the force is given by Newton's Second Law: a = F/m, where a is the acceleration and m is the mass. Hence you can see the acceleration is proportional to q/m -- the charge to mass ratio. Since the acceleration determines the path of the particle, all particles with the same q/m follow the same path.

There's a historical angle here, too: because all particles with the same q/m follow the same path, any experiment using electric and magnetic fields only will be unable to determine the charge of a particle. So, for example, when the electron was first discovered, it was easy to measure the q/m of the electron, by doing experiments with electric and magnetic fields. But it was not possible to measure the charge itself, or the mass itself! This is certainly annoying.

The problem was solved by the ingenious Millikan oil-drop experiment, in which use was made of the force of gravity as well as an electric field. The addition of this extra force allowed the mass and charge of the electron to be determined separately. But it was a very, very tricky experiment, difficult to perform.

Answer 5

Thanx a lot Carl