Question

In a cathode ray oscillograph, the focusing of beam on the screen is achieved by

• A. Convex lens
• B. Magnetic field
• C. Electric potential
• D. All of these

Answer 1

The correct option is C Electric potential

In the oscilloscope, the signal to be studied is first amplified and then applied to the vertical plate to deflect the beam vertically and at the same time, a voltage that increases linearly with time is applied to the horizontal plate thus causing the beam to be deflected horizontally. The signal applied to the vertical plate is thus displayed on the screen as a function of time.

Hence focussing of beam on screen is achieved by changing electric potential or the voltage with time across the horizontal plate.