1.31 It is now believed that protons and neutrons (which constitute nuclei of ordinary matter) are themselves built out of more elementary units called quarks. A proton and a neutron consist of three quarks each. Two types of quarks, the so called ‘up’ quark (denoted by u) of charge + \left ( \frac{2}{3} \right ) e, and the ‘down’ quark (denoted by d) of charge \left (- \frac{1}{3} \right ) e, together with electrons build up ordinary matter. (Quarks of other types have also been found which give rise to different unusual varieties of matter.) Suggest a possible quark composition of a proton and neutron.

Answers (1)

Given, a proton and a neutron consist of three quarks each.

And, ‘up’ quark is of charge + \left ( \frac{2}{3} \right ) e, and the ‘down’ quark of charge \left (- \frac{1}{3} \right ) e

Let the number of 'up' quarks be n. Therefore, the number of 'down' quarks is (3-n).

 \therefore The net charge = \\ n\times\frac{2}{3}e + (3-n)\frac{-1}{3}e = (n-1)e

Now, A proton has a charge +1e

\therefore (n-1)e = +1e \implies n =2

Proton will have 2 u and 1 d, i.e, uud

Similarly, neutron has a charge 0

\therefore (n-1)e = 0 \implies n =1

Neutron will have 1 u and 2 d, i.e, udd

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