Example 4
a)
estimate the electric field strength at a point x that is 10 nm from a gold nucleus, which
is assumed to be a point charge (atomic number: gold, 79)

E = 1.14 x 10⁹ V/m

Explanation:

Given,

The atomic number of gold, A = 79

The number of protons present in the nucleus, p = 79

The charge of a proton, q = 1.602 x 10⁻¹⁹ C

Therefore the total charge is, Q = 79 x 1.602 x 10⁻¹⁹

                                                     = 1.26558 x 10⁻¹⁷ C

The distant from the point charge, x = 10 nm

The electric field strength at a distant x is given by,

                                        V/m

                = 9 x 10⁹ Nm²C⁻²

Substituting the values in the above equation

                                         E =  (9 x 10⁹  X 1.26558 x 10⁻¹⁷) / (10 x 10⁻⁹)²

                                          E = 1.14 x 10⁹ V/m  

Hence, the electric field strength is, E = 1.14 x 10⁹ V/m                      

work: w = fd (given)

work done by chet   =50*1 = 50 j

work done by mika =40*2 = 80 j

work done by sara =30*1.5 = 45 j

work done by bill =60*0.5 = 30 j

students in order from the greatest amount of work done to the least is mika> chet> sara> bill

hence option (b) is correct.