NEET Electric Charges and Fields — Set 18

Question 1

A thin spherical shell of radius 12 cm has $ q = 10 \, \mu\text{C} $. What is the electric field at 14 cm from the center?

Accepted Answer

Outside shell: $ E = \frac{k q}{r^2} $. $ E = 9 \times 10^9 \times \frac{10 \times 10^{-6}}{(0.14)^2} = 9 \times 10^9 \times \frac{10 \times 10^{-6}}{0.0196} = 4.59 \times 10^6 \, \text{N/C} $.

Question 2

A closed surface has a net flux of $ 7.91 \times 10^5 \, \text{Nm}^2/\text{C} $. What is the charge enclosed?

Accepted Answer

$ \phi = \frac{q}{\varepsilon_0} $. $ q = \phi \varepsilon_0 = 7.91 \times 10^5 \times 8.854 \times 10^{-12} = 7 \times 10^{-6} \, \text{C} = 7 \, \mu\text{C} $.

Question 3

A conducting sphere of radius 30 cm has a surface charge density of $ 50 \, \mu\text{C/m}^2 $. What is the total charge on it?

Accepted Answer

Surface area: $ A = 4 \pi r^2 = 4 \pi (0.3)^2 = 0.36 \pi \, \text{m}^2 $. Charge: $ q = \sigma A = 50 \times 10^{-6} \times 0.36 \pi = 5.654 \times 10^{-5} \, \text{C} $.

NEET Physics: Electric Charges and Fields — Practice Set 18

Q1. A thin spherical shell of radius 12 cm has \( q = 10 \, \mu\text{C} \). What is the electric field at 14 cm from the center?

Q2. A closed surface has a net flux of \( 7.91 \times 10^5 \, \text{Nm}^2/\text{C} \). What is the charge enclosed?

Q3. A conducting sphere of radius 30 cm has a surface charge density of \( 50 \, \mu\text{C/m}^2 \). What is the total charge on it?

Q4. Two point charges \( q_1 = 4 \, \mu\text{C} \) and \( q_2 = -6 \, \mu\text{C} \) are placed 20 cm apart in vacuum. What is the magnitude of the electrostatic force between them?

Q5. Two point charges \( 6 \times 10^{-7} \, \text{C} \) and \( 9 \times 10^{-7} \, \text{C} \) are 45 cm apart in air. What is the magnitude of the force between them?

Q6. A thin spherical shell of radius 15 cm has \( q = 6 \, \mu\text{C} \). What is the electric field at 10 cm from the center?

Q7. What ensures that electric field lines never cross each other in a static field configuration?

Q8. What ensures that the electric field inside a hollow conductor remains zero even if an external charge is placed nearby?

Q9. A dipole with \( p = 9 \times 10^{-9} \, \text{C m} \) is at 90° to a field \( E = 3 \times 10^4 \, \text{N/C} \). What is the torque?

Q10. What explains why the electric field due to a charged object can penetrate an insulator but not a conductor?