# In a Tv Picture Tube, Electrons Are Ejected from the Cathode with Negligible Speed and They Attain a Velocity of 5 × 106 M/S in Travelling - Physics

Sum

In a TV picture tube, electrons are ejected from the cathode with negligible speed and they attain a velocity of 5 × 106 m/s in travelling one centimetre. Assuming straight-line motion, find the constant force exerted on the electrons. The mass of an electron is 9.1 × 10−31 kg.

#### Solution

Initial velocity of the electrons is negligible, i.e. u = 0.
Final velocity of the electrons, v = 5 × 106 m/s
Distance travelled by the electrons,
s = 1 cm = 1 × 10−2 m
∴ Acceleration, $a = \frac{v^2 - u^2}{2 S}$
$\Rightarrow a = \frac{\left( 5 \times {10}^5 \right)^2 - 0}{2 \times 1 \times {10}^{- 3}} = \frac{25 \times {10}^{12}}{2 \times {10}^{- 2}}$

$\Rightarrow a = 12 . 5 \times {10}^{14} m/ s^2$
So, force on the electrons, F = ma
⇒ F = 9.1 × 10−31 × 12.5 × 10−14
= 1.1 × 10−15 N
Concept: Newton’s Second Law of Motion
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#### APPEARS IN

HC Verma Class 11, Class 12 Concepts of Physics Vol. 1
Chapter 5 Newton's Laws of Motion
Q 3 | Page 79