NEET Electric Charges and Fields — Set 2

Question 1

An infinite line charge has $ E = 4.5 \times 10^5 \, \text{N/C} $ at 4 cm. What is $ \lambda $?

Accepted Answer

$ E = \frac{2 k \lambda}{r} $. $ 4.5 \times 10^5 = \frac{2 \times 9 \times 10^9 \times \lambda}{0.04} $. $ \lambda = \frac{4.5 \times 10^5 \times 0.04}{18 \times 10^9} = 1 \times 10^{-6} \, \text{C/m} $.

Question 2

Two charges $ +7 \, \mu\text{C} $ and $ -5 \, \mu\text{C} $ are 60 cm apart. What is the electric field magnitude at the midpoint?

Accepted Answer

Midpoint distance = 30 cm = 0.3 m. $ E_1 = 9 \times 10^9 \times \frac{7 \times 10^{-6}}{(0.3)^2} = 7 \times 10^5 \, \text{N/C} $ (towards $ -5 \, \mu\text{C} $). $ E_2 = 9 \times 10^9 \times \frac{5 \times 10^{-6}}{(0.3)^2} = 5 \times 10^5 \, \text{N/C} $ (towards $ -5 \, \mu\text{C} $). Net $ E = 7 \times 10^5 + 5 \times 10^5 = 1.2 \times 10^6 \, \text{N/C} $.

Question 3

A body loses $ 3.2 \times 10^{-8} \, \text{C} $ of charge when rubbed. How many electrons were transferred from it?

Accepted Answer

Losing charge means electrons are removed, so charge is positive. $ q = n e $, $ e = 1.6 \times 10^{-19} \, \text{C} $. $ n = \frac{q}{|e|} = \frac{3.2 \times 10^{-8}}{1.6 \times 10^{-19}} = 2 \times 10^{11} $.

NEET Physics: Electric Charges and Fields — Practice Set 2

Q1. An infinite line charge has \( E = 4.5 \times 10^5 \, \text{N/C} \) at 4 cm. What is \( \lambda \)?

Q2. Two charges \( +7 \, \mu\text{C} \) and \( -5 \, \mu\text{C} \) are 60 cm apart. What is the electric field magnitude at the midpoint?

Q3. A body loses \( 3.2 \times 10^{-8} \, \text{C} \) of charge when rubbed. How many electrons were transferred from it?

Q4. An infinite line charge produces \( E = 3.6 \times 10^5 \, \text{N/C} \) at 5 cm. What is \( \lambda \)?

Q5. A uniform field \( E = 7 \times 10^3 \, \text{N/C} \) is along the z-axis. What is the flux through a circle of radius 10 cm in the xy-plane?

Q6. A point charge \( 7 \, \mu\text{C} \) is at the origin. What is the electric field magnitude at a point 4 m along the y-axis?

Q7. A plane sheet has \( \sigma = 8.85 \times 10^{-11} \, \text{C/m}^2 \). What is the electric field near it?

Q8. A point charge \( 15 \, \mu\text{C} \) is at the origin. What is the electric field magnitude at a point 6 m along the y-axis?

Q9. What ensures that the electric field is always radial for an infinitely long, uniformly charged wire?

Q10. What ensures that the electric field outside a uniformly charged spherical shell behaves as if all charge were concentrated at its center?

Q11. What principle explains why the net electric flux through a closed surface depends only on the charge enclosed within it?

Q12. A body loses \( 8.0 \times 10^{-8} \, \text{C} \) of charge when rubbed. How many electrons were transferred from it?

Q13. Three charges \( +6 \, \mu\text{C}, -3 \, \mu\text{C}, +3 \, \mu\text{C} \) are at the vertices of an equilateral triangle of side 1 m. What is the force magnitude on \( +6 \, \mu\text{C} \)?

Q14. A thin spherical shell of radius 32 cm has \( q = 9 \, \mu\text{C} \). What is the electric field at 25 cm from the center?

Q15. A thin spherical shell of radius 18 cm has a charge of \( 12 \, \mu\text{C} \). What is the electric field at a point 20 cm from the center?