Question

In a region where intensity of electric field is $5N{C}^{-1}$ , $40$ lines of electric force are crossing per square metre. The number of lines crossing per square metre where intensity of electric field is $10N{C}^{-1}$ will be :

• A. $20$
• B. $80$
• C. $100$
• D. $200$

Answer 1

Answer: (B)

$80$

Number of lines of electric force crossing is equal to flux $\left(\varphi \right)$
We know $\varphi =\int E.da$
$\to$ By keeping area constant and doubling E, $\varphi$ will also get doubled.
$\therefore$ Number of lines get doubled $=80$