A thin, flat washer is a disk with an outer diameter of 14 cm and a hole in the center with a diameter of 7 cm. The washer has a uniform charge distribution and a total charge of 8 nC. What is the electric field on the axis of the washer at a distance of 33 cm from the center of the washer? (Enter the magnitude of the electric field.)

2583.9 N/C

Explanation:

Parameters given:

Outer diameter = 14 cm

Outer radius, R = 7cm = 0.07m

Inner diameter = 7 cm

Inner radius, r = 3.5 cm = 0.035m

Charge of washer = 8 nC = 8 * 10^ (-9) C

Distance from washer, z = 33 cm = 0.33m

The electric field due to a washer (hollow disk) is given as:

E = k * σ * 2π [ 1 - z / (√ (z² + R²) ]

Where σ = charge per unit area

σ = q/π (R² - r²)

σ = 8 * 10^ (-9) / (π * (0.07 - 0.035) ²)

σ = 2.077 * 10^ (-6) C/m²

=> E = 9 * 10^9 * 2.077 * 10^ (-6) * 2π * [1 - 0.33 / (√ (0.33² + 0.07²) ]

E = 117.467 * 10^3 * (1 - 0.978)

E = 117.467 * 10^3 * 0.022

E = 2583.9 N/C