According to Gauss' law, the electric field outside a spherical surface uniformly charged is equal to the electric field if the whole charge were concentrated at the center of the sphere.
Therefore, when you are outside two spheres, the electric field will be the overlapping of the two electric fields:
E(r > r₂ > r₁) = k · q₁/r² + k · q₂/r² = k · (q₁ + q₂) / r²
where:
k = 9×10⁹ N·m²/C²
We have to transform our data into the correct units of measurement:
q₁ = 8.0 pC = 8.0×10⁻¹² C
q₂ = 3.0 pC = 3.0×10<span>⁻¹² C
</span><span>r = 5.0 cm = 0.05 m
Now, we can apply the formula:
</span><span>E(r) = k · (q₁ + q₂) / r²
= </span>9×10⁹ · (8.0×10⁻¹² + 3.0×10⁻¹²) / (0.05)²
= 39.6 N/C
Hence, <span>the magnitude of the electric field 5.0 cm from the center of the two surfaces is E = 39.6 N/C</span>
There are no inaccurate items on the list you provided.
And what does 'the following" mean anyway ?
Answer:
a) 0.142mH
b) 14mV
Explanation:
the complete answer is:
(a) Calculate the self-inductance of a solenoid that is <ghtly wound with wire of diameter 0.10 cm, has a cross-sec<onal area of 0.90 cm2 , and is 40 cm long. (b) If the current through the solenoid decreases uniformly from 10 to 0 A in 0.10 s, what is the emf induced between the ends of the solenoid
a) the self inductance of a solenoid is given by:

μo: magnetic permeability of vacuum = 4\pi*10^{-7}N/A^2
A: cross sectional area = 0.9cm^2=9*10^{-5}m
L: length of the solenoid = 40cm = 0.4m
The N turns of the wire is calculated by using the diameter of the wire:
N = (40cm)/(0.10cm)=400
By replacing in the formula you obtain:

the self inductance is 1.42*10^{-4}H = 0.142mH
b) to find the emf you can use:

the emf induced is 14mV
<span>A phase change is an example of a
Physial change</span>