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# Consider the Following Very Rough Model of a Beryllium Atom. the Nucleus Has Four Protons and Four Neutrons Confined to a Small Volume of Radius 10−15 M. - Physics

ConceptElectric Field Introduction of Electric Field

#### Question

Consider the following very rough model of a beryllium atom. The nucleus has four protons and four neutrons confined to a small volume of radius 10−15 m. The two 1 selectrons make a spherical charge cloud at an average distance of 1⋅3 ×10−11 m from the nucleus, whereas the two 2 s electrons make another spherical cloud at an average distance of 5⋅2 × 10−11 m from the nucleus. Find three electric fields at (a) a point just inside the 1 s cloud and (b) a point just inside the 2 s cloud.

#### Solution

(a)
Let us consider the three surfaces as three concentric spheres A, B and C.
Let us take q = 1.6× 10-19 C .

Sphere A is the nucleus; so, the charge on sphere A, q1 = 4q
Sphere B is the sphere enclosing the nucleus and the 2 1s electrons; so charge on this sphere, q2 = 4q -2q = 2q
Sphere C is the sphere enclosing the nucleus and the 4 electrons of Be; so, the charge enclosed by this sphere,

q3 = 4q -4q = 0

Radius of sphere A, r1 = 10-15 m

Radius of sphere B, r2 = 1.3 × 10-11 m

Radius of sphere C, r3 = 5.2 × 10-11 m

As the point 'P' is just inside the spherical cloud 1s, its distance from the centre

x = 1.3 × 10-11 m

Electric field,

"E" = q/(4 pi ∈_0 "x"^2)

Here, the charge enclosed is due to the charge of the 4 protons inside the nucleus . So,

"E" = (4 xx (1.6 xx 10^-19))/(4 xx 3.14 xx (8.85 xx 10^-12)xx ( 1.3 xx 10^-11)^2 )

E = 3.4× 1013  N/C

(b)
For a point just inside the 2s cloud, the total charge enclosed will be due to the 4 protons and 2 electrons. Charge enclosed,

qen = 2q = 2× (1.6 ×10-19) C

Hence, electric field,

"E" = ("q"_"en")/ (4 pi ∈_0"x"^2)

x = 5.2× 10-11 m

"E" = (2 xx (1.6 xx 10^-19))/(4 xx 3.14 xx ( 8.85 xx 10^-12) xx ( 5.2 xx 10^-11)^2)

E = 1.065 × 1012 N/C

Thus , E =1.1× 1012 N/C

Is there an error in this question or solution?

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Solution Consider the Following Very Rough Model of a Beryllium Atom. the Nucleus Has Four Protons and Four Neutrons Confined to a Small Volume of Radius 10−15 M. Concept: Electric Field - Introduction of Electric Field.
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