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 a neutron.

Solution

Charge on 'up' quark,    $(u) = + \frac{2}{3} e$
Charge on 'down' quark, $(d) = - \frac{1}{3} e$
Charge on a proton = e
Charge on a neutron = 0

Let a proton contains x ‘up’ quarks and (3 - x) ‘down’ quarks. Then total charge on a proton is

$ux + d (3 - x) = e$

$\Rightarrow$    $+ \frac{2}{3} ex - \frac{1}{3} e (3 - x) = e$

$\Rightarrow$    $+ \frac{2}{3} x - 1 + \frac{x}{3} = 1$

$\Rightarrow$ x = 2

and 3 - x = 3 - 2 = 1

i.e., proton contains 2 ‘up’ quarks and 1 ‘down’ quark. Its quark composition should be uud.

Let a neutron contains y ‘up’ quarks and (3 – y) ‘down’ quarks. Then total charge on a neutron is
   $ny + d (3 - y) = 0$

$\Rightarrow$ $+ \frac{2}{3} ey - \frac{1}{3} e (3 - y) = 0$

$\Rightarrow$ $+ \frac{2}{3} y - 1 + \frac{y}{3} = 1$

$\Rightarrow$    $y = 1$

and   3 – y = 3 – 1 = 2
i.e., neutrons contain 1 ‘up’ quark and 2 ‘down’ quarks. Its quark composition should be udd.

Some More Questions From Electric Charges and Fields Chapter

a) An electrostatic field line is a continuous curve. That is, a field line cannot have sudden breaks. Why not?
b) Explain why two field lines never cross each other at any point?

Figure shows tracks of three charged particles in a uniform electrostatic field. Give the signs of the three charges. Which particle has the highest charge to mass ratio?

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Electric Charges And Fields

Some More Questions From Electric Charges and Fields Chapter

a) An electrostatic field line is a continuous curve. That is, a field line cannot have sudden breaks. Why not?
b) Explain why two field lines never cross each other at any point?

Figure shows tracks of three charged particles in a uniform electrostatic field. Give the signs of the three charges. Which particle has the highest charge to mass ratio?

Mock Test Series

NCERT Sample Papers

Entrance Exams Preparation

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Location

For Daily Free Study Material Join wiredfaculty

Electric Charges And Fields

Some More Questions From Electric Charges and Fields Chapter

a) An electrostatic field line is a continuous curve. That is, a field line cannot have sudden breaks. Why not?b) Explain why two field lines never cross each other at any point?

Figure shows tracks of three charged particles in a uniform electrostatic field. Give the signs of the three charges. Which particle has the highest charge to mass ratio?

Mock Test Series

NCERT Sample Papers

Entrance Exams Preparation

a) An electrostatic field line is a continuous curve. That is, a field line cannot have sudden breaks. Why not?
b) Explain why two field lines never cross each other at any point?