Question

In Thomson's experiment, a magnetic field of induction ${10}^{-2}{\text{Wb m}}^{-2}$ is used. For an undeflected beam of cathode rays, a potential difference of $500\text{V}$ is applied between the plates, which are $0.5\text{cm}$ apart. Then the velocity of the cathode ray beam is (in ${\text{ms}}^{-1}$).

• A. $4\times {10}^7$
• B. $1\times {10}^7$
• C. $2\times {10}^7$
• D. $3\times {10}^7$

Answer 1

The correct option is B $1\times {10}^7$

Given,

$B={10}^{-2}{\text{Wb m}}^{-2};V=500\text{V};d=0.5\text{cm}$

The velocity of cathode ray beam is,

$v=\frac{E}{B}=\frac{V}{Bd}[\because E=\frac{V}{d}]$

$=\frac{500}{{10}^{-2}\times 0.5\times {10}^{-2}}=\frac{5}{5}\times {10}^7$

$=1\times {10}^7{\text{ms}}^{-1}$

<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> Hence, $\left(B\right)$ is the correct answer.