NEET Electric Charges and Fields — Set 1

Question 1

Which principle underlies the fact that the electric field due to a system of charges can be analyzed by considering each charge independently?

Accepted Answer

The superposition principle allows the total electric field to be the vector sum of fields from individual charges, assuming each field is unaffected by others. This linearity stems from the nature of electrostatic forces, enabling independent analysis.

Question 2

A dipole with charges $ +4 \, \mu\text{C} $ and $ -4 \, \mu\text{C} $ separated by 2 mm is in a field $ 7 \times 10^4 \, \text{N/C} $ at 30°. What is the torque?

Accepted Answer

Dipole moment: $ p = q \times 2a = 4 \times 10^{-6} \times 2 \times 10^{-3} = 8 \times 10^{-9} \, \text{C m} $. Torque: $ \tau = p E \sin \theta = 8 \times 10^{-9} \times 7 \times 10^4 \times \sin 30^\circ = 5.6 \times 10^{-4} \times 0.5 = 2.8 \times 10^{-4} \, \text{N m} $.

Question 3

A thin spherical shell of radius 22 cm has $ q = 15 \, \mu\text{C} $. What is the electric field at 26 cm from the center?

Accepted Answer

Outside shell: $ E = \frac{k q}{r^2} $. $ E = 9 \times 10^9 \times \frac{15 \times 10^{-6}}{(0.26)^2} = 9 \times 10^9 \times \frac{15 \times 10^{-6}}{0.0676} = 1.996 \times 10^6 \, \text{N/C} $.

NEET Physics: Electric Charges and Fields — Practice Set 1

Q1. Which principle underlies the fact that the electric field due to a system of charges can be analyzed by considering each charge independently?

Q2. A dipole with charges \( +4 \, \mu\text{C} \) and \( -4 \, \mu\text{C} \) separated by 2 mm is in a field \( 7 \times 10^4 \, \text{N/C} \) at 30°. What is the torque?

Q3. A thin spherical shell of radius 22 cm has \( q = 15 \, \mu\text{C} \). What is the electric field at 26 cm from the center?

Q4. Three equal charges \( q = 3 \, \mu\text{C} \) are at the vertices of an equilateral triangle of side 1 m. What is the electric field at the centroid?

Q5. Why does the electric field due to a uniformly charged infinite plane remain unaffected by the distance from the plane?

Q6. A closed surface has a net flux of \( 6.78 \times 10^5 \, \text{Nm}^2/\text{C} \). What is the charge enclosed?

Q7. A dipole with \( p = 7 \times 10^{-9} \, \text{C m} \) is at 45° to a field \( E = 4 \times 10^4 \, \text{N/C} \). What is the torque?

Q8. A charge of \( 11 \, \mu\text{C} \) is at the center of a cube of edge 45 cm. What is the total flux through the cube?

Q9. Two point charges \( -3 \times 10^{-7} \, \text{C} \) and \( 5 \times 10^{-7} \, \text{C} \) are 80 cm apart in vacuum. What is the magnitude of the force between them?

Q10. A dipole with moment \( p = 5 \times 10^{-9} \, \text{C m} \) is at 60° to a uniform field \( E = 4 \times 10^4 \, \text{N/C} \). What is the torque magnitude?

Q11. What explains why the electric field due to a dipole can be zero at certain points along its equatorial plane?

Q12. Two charges \( +5 \, \mu\text{C} \) and \( -7 \, \mu\text{C} \) are 35 cm apart. What is the electric field magnitude at the midpoint?

Q13. Three charges \( +8 \, \mu\text{C}, -4 \, \mu\text{C}, +2 \, \mu\text{C} \) are at the vertices of an equilateral triangle of side 1.8 m. What is the force magnitude on \( +8 \, \mu\text{C} \)?

Q14. 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 25 cm in the xy-plane?

Q15. A glass rod loses \( 6.4 \times 10^{-8} \, \text{C} \) of charge when rubbed with silk. How many electrons were transferred from it?