NEET Electric Charges and Fields — Set 15

Question 1

Two point charges $ 7 \times 10^{-7} \, \text{C} $ and $ -2 \times 10^{-7} \, \text{C} $ are 70 cm apart in vacuum. What is the magnitude of the force between them?

Accepted Answer

Using Coulomb’s law: $ F = k \frac{|q_1 q_2|}{r^2} $. $ k = 9 \times 10^9 \, \text{Nm}^2/\text{C}^2 $, $ q_1 = 7 \times 10^{-7} \, \text{C} $, $ q_2 = -2 \times 10^{-7} \, \text{C} $, $ r = 0.7 \, \text{m} $. $ |q_1 q_2| = 7 \times 2 \times 10^{-14} = 14 \times 10^{-14} \, \text{C}^2 $. $ r^2 = (0.7)^2 = 0.49 \, \text{m}^2 $. $ F = 9 \times 10^9 \times \frac{14 \times 10^{-14}}{0.49} = 9 \times 10^9 \times 2.857 \times 10^{-13} = 0.00257 \, \text{N} $.

Question 2

A uniform field $ E = 9 \times 10^3 \, \text{N/C} $ is along the x-axis. What is the flux through a rectangle of 35 cm × 45 cm in the yz-plane?

Accepted Answer

Area: $ A = 0.35 \times 0.45 = 0.1575 \, \text{m}^2 $. Flux: $ \phi = E A \cos 0^\circ = 9 \times 10^3 \times 0.1575 = 1417.5 \, \text{Nm}^2/\text{C} $.

Question 3

An infinite line charge has $ \lambda = 9 \times 10^{-7} \, \text{C/m} $. What is the electric field at 30 cm?

Accepted Answer

$ E = \frac{2 k \lambda}{r} $, $ k = 9 \times 10^9 \, \text{Nm}^2/\text{C}^2 $. $ E = \frac{2 \times 9 \times 10^9 \times 9 \times 10^{-7}}{0.3} = 5.4 \times 10^4 \, \text{N/C} $.

NEET Physics: Electric Charges and Fields — Practice Set 15

Q1. Two point charges \( 7 \times 10^{-7} \, \text{C} \) and \( -2 \times 10^{-7} \, \text{C} \) are 70 cm apart in vacuum. What is the magnitude of the force between them?

Q2. A uniform field \( E = 9 \times 10^3 \, \text{N/C} \) is along the x-axis. What is the flux through a rectangle of 35 cm × 45 cm in the yz-plane?

Q3. An infinite line charge has \( \lambda = 9 \times 10^{-7} \, \text{C/m} \). What is the electric field at 30 cm?

Q4. Why does the electric field near a charged surface exhibit a sharp increase in strength compared to regions further away?

Q5. A thin spherical shell of radius 10 cm has \( q = 8 \, \mu\text{C} \). What is the electric field at 15 cm from the center?

Q6. What property of the electric field allows it to exert a force on a charge without physical contact?

Q7. A thin spherical shell of radius 28 cm has \( q = 8 \, \mu\text{C} \). What is the electric field at 20 cm from the center?

Q8. In an experiment, a charged object is brought near a neutral conductor, causing charge separation. What phenomenon is responsible for this effect?

Q9. An infinite line charge has \( \lambda = 7 \times 10^{-7} \, \text{C/m} \). What is the electric field at 25 cm?

Q10. Two point charges \( 6 \times 10^{-7} \, \text{C} \) and \( 10 \times 10^{-7} \, \text{C} \) are 120 cm apart in vacuum. What is the magnitude of the force between them?