In a television picture tube, electrons are accelerated by thousands of volts th

Question

In a television picture tube, electrons are accelerated by thousands of volts through a vacuum towards the screen.
(a). If a TV set were laid on its back, what potential difference, acting over a distance of 15 cm, would be needed to balance the downward force of gravity so that an electron would remain stationary?
(b). Given the normal TV voltage, would electrons still be able to move upward towards the screen when laid on its back, against the force of gravity? Could they accelerate? Show calculations to support your answer.

Explanation / Answer

Electric force   Fe = Vq / r fravitayional force acting on the electron Fg   =   mg mg =   Vq / r   == >     potential differece V   = mgr / q Here m = mass of the electron = 9.1*10-31 kg q   = charge of the electron = 1.6*10-19 C g = accelaration due to gravity   = 9.8 m/s^2 r = 0.15 m plug all values we get V   = 8.3*10^-12 V --------------------------------------------- (b) Normal TV Voltage is 120 V >> 8.3*10^-12 V   hence the electorns should accelarate

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