Answer:
a) E = 8.63 10³ N /C, E = 7.49 10³ N/C
b) E= 0 N/C, E = 7.49 10³ N/C
Explanation:
a) We can apply Gauss's law for this problem,
Ф = ∫ E. dA =
/ε₀
By taking a spherical Gaussian surface, the electric field lines are parallel to the sphere's radius, simplifying the scalar product to an algebraic one.
The surface area of a sphere is given by:
A = 4π r²
Using the density formula:
ρ = q_{int} / V
q_{int} = ρ V
The sphere's volume is calculated as:
V = 4/3 π r³
Substituting in, we get:
E 4π r² = ρ (4/3 π r³) /ε₀
E = ρ r / 3ε₀
The density then is:
ρ = Q / V
V = 4/3 π a³
E = Q 3 / (4π a³) r / 3ε₀
k = 1 / 4π ε₀
E = k Q r / a³
Let’s calculate for:
for r = 4.00cm = 0.04m
E = 8.99 10⁹ 3.00 10⁻⁹ 0.04 / 0.05³
E = 8.63 10³ N / C
When r = 6.00 cm:
the Gaussian surface envelops the sphere entirely, capturing all the charge:
E (4π r²) = Q /ε₀
E = k q / r²
Calculating again:
E = 8.99 10⁹ 3 10⁻⁹ / 0.06²
E = 7.49 10³ N/C
b) Now, let’s repeat the calculations considering a conducting sphere.
For r = 4 cm:
All charge is on the sphere's surface due to the repulsion of charges, resulting in zero field inside:
E = 0
For r = 0.06 m, all charge is contained within the Gaussian surface, thus:
E = k q / r²
E = 7.49 10³ N / C