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Home/ Questions/Q 7169
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Ashok0210
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Ashok0210
Asked: February 13, 20212021-02-13T07:34:14+00:00 2021-02-13T07:34:14+00:00In: Class 12 Physics

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 + (2/3) e, and the ‘down’ quark (denoted by d) of charge (–1/3) 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.

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Class-12th Physics, CBSE and UP Board
Electric Charges and Fields,
Chapter-1, Exercise -1, Additional Exercise, Q-1.1
NCERT Solutions for Class 12th Physics

2020-2021cbsechapter 1class 12 physicsclass 12thclass 12th scienceelectric charges and fieldsncertncert solutionsphysics
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      Pawan1308
      2021-02-18T14:47:46+00:00Added an answer on February 18, 2021 at 2:47 pm

      A proton has three quarks. Let there be n up quarks in a proton, each having a charge of (+2/3) e.

      Charge due to n up quarks =(2/3 x e)n

      Number of down quarks in a proton = 3 – n

      Each down quark has a charge of = -1/3 x e

      Charge due to (3 – n) down quarks =  (-1/3 x e) (3 — n)

      Total charge on a proton = + e

      Therefore e = (2/3 x e) n + (-1/3 x e) (3 — n)

      => e = 2ne/3  – e + ne/3

      => 2 e = ne => n = 2

      Number of up quarks in a proton, n = 2

      Number of down quarks in a proton = 3- n = 3 — 2 = 1 .

      Therefore, a proton can be represented as ‘uud’.

      A neutron also has three quarks. Let there be n up quarks in a neutron.

      Charge on a neutron due to n up quarks = (+2/3 e )n

      Number of down quarks is  3-n ,and each having a charge of -1/3 e.

      Charge on a neutron due to (3-n) down quarks = (-1/3e) (3-n)

      Total charge on a neutron =0

      Therefore 0=(2/3 x e) n + (-1/3 x e) (3-n)

      =>  0 = 2ne/3  –  e  +  ne/3

      => e= ne =>n=1

      Number of up quarks in a neutron ,n=1

      Number of down quarks in a neutron=3-n =2

      Therefore, a neutron can be represented as ‘udd’.

       

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