My question is regarding the direction in which cathode rays bend in a magnetic field.
My book states that :
When only electric field is applied, the electrons deviate from their
path and hit the cathode ray tube at point A. Similarly when only
magnetic field is applied , the electron strikes the cathode ray tube
at point C.
I tried to apply the Fleming's Left hand rule used to find the direction of force on a current carrying wire where the direction of current is taken opposite to the direction of flow of electrons.
The Fleming's Left hand rule states that :
Stretch the thumb, forefinger and middle finger of your left hand such
that they are mutually perpendicular. If the first finger points in
the direction of magnetic field and the second finger in the direction
of current, then the thumb will point in the direction of motion or
the force acting on the conductor.
Applying this rule I found that the electrons should hit the cathode ray tube at A in a magnetic field . But in the book it is given that they strike it at C.
Edit : I am adding a picture which makes it clear how I applied the rule.
Please explain me where I went wrong . Thank you.
Best Answer
You're right, and your book is wrong. The magnetic field is coming out of the page. The velocity vector of the electrons is to the right. The magnetic force acting on the electrons is $-e\textbf{v}\times\textbf{B}$, which is up. The is contrary to the information stated in the quote in the book. The deflection should be up.