Math Problem Statement

A circular loop of radius R=0.2 mR = 0.2 , \text{m}R=0.2m is placed in a uniform electric field E\mathbf{E}E of magnitude 500 N/C500 , \text{N/C}500N/C. The plane of the loop makes an angle of 30∘30^\circ30∘ with the direction of the electric field.

Calculate the electric flux through the loop.

If the loop is rotated such that it becomes perpendicular to the field, what will the flux be?

Solution

1. Electric Flux Calculation

The electric flux ΦE\Phi_E through a surface is given by:

ΦE=EAcos(θ)\Phi_E = E \cdot A \cdot \cos(\theta)

Where:

  • E=500N/CE = 500 \, \text{N/C} (electric field magnitude)
  • A=πR2A = \pi R^2 (area of the loop)
  • R=0.2mR = 0.2 \, \text{m} (radius of the loop)
  • θ=30\theta = 30^\circ (angle between the electric field and the normal to the loop's surface)

Step 1: Calculate Area

A=π(0.2)2=0.04πm2A = \pi (0.2)^2 = 0.04\pi \, \text{m}^2

Step 2: Substitute Values

ΦE=500×0.04π×cos(30)\Phi_E = 500 \times 0.04\pi \times \cos(30^\circ)

Since cos(30)=320.866\cos(30^\circ) = \frac{\sqrt{3}}{2} \approx 0.866,

ΦE500×0.04π×0.866\Phi_E \approx 500 \times 0.04\pi \times 0.866

ΦE54.4Nm2/C\Phi_E \approx 54.4 \, \text{Nm}^2/\text{C}


2. Flux When Loop is Perpendicular

When the loop is rotated such that its plane is perpendicular to the electric field, the angle θ\theta becomes 00^\circ, so:

ΦE=EAcos(0)=EA\Phi_E = E \cdot A \cdot \cos(0^\circ) = E \cdot A

ΦE=500×0.04π\Phi_E = 500 \times 0.04\pi

ΦE62.83Nm2/C\Phi_E \approx 62.83 \, \text{Nm}^2/\text{C}


Final Answer:

  1. Electric flux at 3030^\circ: ΦE54.4Nm2/C\Phi_E \approx 54.4 \, \text{Nm}^2/\text{C}
  2. Electric flux when perpendicular: ΦE62.83Nm2/C\Phi_E \approx 62.83 \, \text{Nm}^2/\text{C}

Would you like a more detailed breakdown of any step?


Related Questions:

  1. How does the electric flux change if the electric field magnitude doubles?
  2. What happens if the radius of the loop is halved?
  3. How does the flux change if the angle becomes 9090^\circ?
  4. How is electric flux affected if the loop is placed in a non-uniform electric field?
  5. What physical quantities influence the electric flux through a surface?

Tip: Electric flux depends on the angle between the field and the normal to the surface, not the surface itself!

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Math Problem Analysis

Mathematical Concepts

Electric Flux
Trigonometry
Area of a Circle

Formulas

Electric flux: Φ_E = E × A × cos(θ)
Area of a circle: A = πR^2

Theorems

Gauss's Law (Concept of Flux)

Suitable Grade Level

Grades 11-12