The deflection sensitivity in a cathode ray oscilloscope (CRO) is ________ the mass of electron. 

Deflection Sensitivity

The deflection sensitivity (S) of a CRT (Cathode Ray Tube) is defined as the deflection (in meters) on the fluorescent screen (D) per volt of the deflecting voltage (E_d).

\(S={D\over E_d}\)

The potential between deflecting plates is given by:

\(E_d={2dE_aD\over LI_d}\)

where, E_d = Potential between deflecting plates

E_a = Accelerating voltage 

d = Distance between deflecting plates

D = Deflection of the electron beam on the screen in the Y direction

L = Distance between screen and center of the deflecting plates

l_d = Length of the deflecting plates

Explanation

Putting the value of E_d in the above formula:

Sensitivity, \(S={D\times LI_d\over 2dE_aD}\)

\(S={Ll_d\over 2dE_a}\)

Magnetic deflection sensitivity:

The Deflection per unit magnetic field intensity is called the magnetic deflection Sensitivity of the tube.

\(S={Ll_d\over \sqrt{E_a}}\sqrt{e\over 2m}\)

∴ The deflection sensitivity in a cathode ray oscilloscope (CRO) is inversely proportional to the square root of the mass of the electron.