KCET · Physics · Electrostatics

The magnitude of point charge due to which the electric field \( 30 \mathrm{~cm} \) away has the magnitude \( 2 \mathrm{~N} C^{-1} \) will be

A \( 2 \times 10^{-11} \mathrm{C} \)
B \( 3 \times 10^{-11} \mathrm{C} \)
C \( 5 \times 10^{-11} \mathrm{C} \)
D \( 9 \times 10^{-11} \mathrm{C} \)

Verified Solution

Answer & Solution

Correct Answer

(A) \( 2 \times 10^{-11} \mathrm{C} \)

Step-by-step Solution

Detailed explanation

Electric field due to a point charge is
\(E=\frac{1}{4 \Pi \varepsilon_{0}} \frac{q}{r^{2}}\)
Given,
\(E=2 N C^{-1} ; r=30 \mathrm{~cm}=30 \times 10^{-2} m ; \frac{1}{4 \Pi \varepsilon_{0}}=9 \times 10^{9} \)
\(\Rightarrow 2=9 \times 10^{9} \times \frac{q}{\left(30 \times 10^{-2}\right)^{2}} \)
\(\Rightarrow q=\frac{2 \times\left(30 \times 10^{-2}\right)^{2}}{9 \times 10^{9}}=2 \times 10^{-11} \mathrm{C}\)
Therefore, magnitude of charge will be \( 2 \times 10^{-11} \mathrm{C} \)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

Same subject

Explore more questions on app

From KCET

Explore more questions on app