Question

Cathode rays are streams of fast moving negatively charged particles. Their speed range is (Consider $c=3\times {10}^{8}m{s}^{-1}$)

• A. $0.1c$ to $0.2c$
• B. $c$
• C. greater than $c$
• D. around ${10}^{-5}c$ to ${10}^{-3}c$

Answer 1

The correct option is A $0.1c$ to $0.2c$

For potential difference 3000 Volt the speed of cathode rays is found to be nearly $3\times {10}^{7}m/s$ which is nearly $0.1c$

formula used is $v=\sqrt[2]{22eV/m}$

put $V=3000V$ and mass of electron $m=9.1\times {10}^{-31}Kg$ ,$e=1.6\times {10}^{-19}C$

If we use higher $v$ then speed can increase so we can say that $v$ ranges from $\text{0.1c to 0.2c}$

Option A is correct.