NEET Electric Charges and Fields — Set 21

Question 1

A thin spherical shell of radius 8 cm has $ q = 4 \, \mu\text{C} $. What is the electric field at 10 cm from the center?

Accepted Answer

Outside shell: $ E = \frac{k q}{r^2} $. $ E = 9 \times 10^9 \times \frac{4 \times 10^{-6}}{(0.1)^2} = 9 \times 10^9 \times \frac{4 \times 10^{-6}}{0.01} = 3.6 \times 10^6 \, \text{N/C} $.

Question 2

An infinite line charge has $ E = 5.4 \times 10^5 \, \text{N/C} $ at 6 cm. What is $ \lambda $?

Accepted Answer

$ E = \frac{2 k \lambda}{r} $. $ 5.4 \times 10^5 = \frac{2 \times 9 \times 10^9 \times \lambda}{0.06} $. $ \lambda = \frac{5.4 \times 10^5 \times 0.06}{18 \times 10^9} = 1.8 \times 10^{-6} \, \text{C/m} $.

Question 3

A metallic sphere of radius 15 cm has a charge of $ 6 \, \mu\text{C} $. What is the electric field just outside its surface?

Accepted Answer

For a conductor, $ E = \frac{k q}{r^2} $ at surface ($ r = 0.15 \, \text{m} $). $ E = 9 \times 10^9 \times \frac{6 \times 10^{-6}}{(0.15)^2} = 2.4 \times 10^6 \, \text{N/C} $.

NEET Physics: Electric Charges and Fields — Practice Set 21

Q1. A thin spherical shell of radius 8 cm has \( q = 4 \, \mu\text{C} \). What is the electric field at 10 cm from the center?

Q2. An infinite line charge has \( E = 5.4 \times 10^5 \, \text{N/C} \) at 6 cm. What is \( \lambda \)?

Q3. A metallic sphere of radius 15 cm has a charge of \( 6 \, \mu\text{C} \). What is the electric field just outside its surface?

Q4. Two charges \( +9 \, \mu\text{C} \) and \( -6 \, \mu\text{C} \) are 45 cm apart. What is the distance from \( +9 \, \mu\text{C} \) where the electric field is zero?

Q5. Which characteristic of insulators prevents them from shielding their interior from an external electric field?

Q6. A uniform electric field \( E = 4 \times 10^3 \, \text{N/C} \) is along the z-axis. What is the flux through a square of side 15 cm in the xy-plane?

Q7. Why can’t the electric field inside a charged insulator be zero, unlike in a conductor?

Q8. What property of electric charges explains why the smallest observable charge is that of an electron or proton?

Q9. Two point charges \( 5 \times 10^{-7} \, \text{C} \) and \( -7 \times 10^{-7} \, \text{C} \) are 150 cm apart in vacuum. What is the magnitude of the force between them?

Q10. A dipole with \( p = 6 \times 10^{-9} \, \text{C m} \) is at 60° to a field \( E = 7 \times 10^4 \, \text{N/C} \). What is the torque?