Aston mass spectrograph is a device to measure atomic masses of isotopes with great precision What is the principle behind this spectrograph.
A. Successfully first the magnetic field and then the electric field at right angles to each other
B. Electric and magnetic fields simultaneously in perpendicular direction
C. Electric and magnetic fields simultaneously and in parallel direction
D. Successfully first the electric field and then the magnetic field at right angles to each other

Hint-Mass spectrograph is a device used to separate and determine masses of isotopes.
Aston mass spectrograph is used to measure velocity independent mass spectrum at a high resolution. In this spectrograph first the collimated charge is deflected by an electric deflector and then by a magnetic deflector

Step by step solution:
We know that a mass spectrograph is a device which is used to separate and determine the masses of isotopes. The specialty of Aston mass spectrograph is that he tried to increase the accuracy of the mass spectrograph by using both electric and magnetic fields to separate isotopes having different masses. The material which is to be tested is placed in the globe of the spectrograph and electric current is used to pull electrons from the atom of the material tested. The beam consisting of these pulled out charged particles is then focused using electric and magnetic fields. First it passes through an electric deflector and then through a magnetic deflector placed at right angles to each other. The precision with which we get the focused spot depends on the mass of the ions. So, the basic principle which makes it different from other mass spectrographs is that it uses both the electric field and magnetic field at right angles to each other so that we can get the measures of atomic mass with high precision.

Hence the correct answer is option D. Successfully first the electric field and then the magnetic field at right angles to each other

Note:A mass spectrograph detects the particles with the help of a photographic plate. Mass spectrometer detects the particles electrically. That is the basic difference between mass spectrometer and mass spectrograph.