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Question -

It is now believed thatprotons and neutrons (which constitute nuclei of ordinary matter) arethemselves built out of more elementary units called quarks. A proton and aneutron 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 upordinary matter. (Quarks of other types have also been found which give rise todifferent unusual varieties of matter.) Suggest a possible quark composition ofa proton and neutron.



Answer -

A proton has three quarks. Let there be n upquarks in a proton, each having a charge of 

Charge due to up quarks

Number of down quarks in aproton = 3 − n

Eachdown quark has a charge of 
Charge due to (3 − n) down quarks 

Total charge on a proton =+ e

Number of up quarks in aproton, n = 2

Number of down quarks in aproton = 3 − n = 3 − 2 = 1

Therefore, a proton can berepresented as ‘uud’.

Aneutron also has three quarks. Let there be n up quarks in aneutron, each having a charge of 

Charge on a neutron due to n upquarks 

Number of down quarks is 3 − n,each havinga charge of

Charge on a neutron due to down quarks = 

Total charge on a neutron= 0

Number of up quarks in aneutron, n = 1

Number of down quarks in aneutron = 3 − n = 2

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

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