[5 Mark Question Answer]

Question 15 Marks

In following fig. shows a mixed source S of alpha and beta particles in a thick lead container. The particles pass through a magnetic field in a direction perpendicular to the plane of paper (inwards as shown by x). State and show in the diagram how the particles get affected.

Answer

(i) Alpha particles are heavy in mass and are positively charged so they are deflected less by magnetic field and direction is upward which can be calculated by Fleming left hand rule.
(ii) Beta particles are negligible in mass so they are highly deflected by magnetic field and they are negatively charge particle so they are deflected in downward direction.
(iii) Gamma radiations have no mass and no charge so they are not deflected by magnetic field.

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Question 25 Marks

A radioactive nucleus ${ }_{\mathrm{Z}}^{\mathrm{A}} \mathrm{X}$ first emits a beta particle and then an alpha particle to give the resulting nucleus ${ }_Q^P Y$ What will be the values of $P$ and $Q$ in terms of $A$ and $Z$ ?

Answer

Initially element is represented by ${ }_z x^A$
$\beta$ particle is represented by $-1 e^{\circ}$ after emitting a $\beta$ particle atomic number of element would increase by 1 unit and mass number of element would remain unchanged.
So after emitting a $\beta$ particle ${ }_z x^A$ would become ${ }_{z+1} x^A$
a particle is rep resented by ${ }_2 He ^4$ this means it contains 2 protons and 2 neutrons so mass of a particle is 4 unit. Thus after emitting a particle mass number of element would decrease by $4$ unit and atomic number of element would decrease by $2.$
So after emitting a particle $_zX^A$ would become $_{z+1-2}X^{A-4} = _{z-1}X^{A-4}.$
The daughter nucleus is represented by $_QY^P.$
$_Qy^P =_{z-1}X^{A-4.}$
$P= A-4.$
$Q= Z-1.$

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Question 35 Marks

A nucleus of an element $X$ which has the symbol ${ }_{84}^{202} \mathrm{X}$ emits an alpha particle and then a beta particle. The final nucleus is ${ }_b^a Y$ Find $a$ and $b$.

Answer

Initia I ly element is rep resented by $_{84}X^{202}$
a particle is rep resented by ${ }_2 He ^4$ this means it contains 2 protons and 2 neutrons so mass of a particle is 4 unit. Thus after emitting a particle mass number of element would decrease by 4 unit and atomic number of element would decrease by 2 .
So after emitting a particle ${ }_{84} X ^{202}$ would become $84-2 X ^{202-4}={ }_{82} X 198$.
$13$ particle is represented by $-1 e^{\circ}$ after emitting a $\beta$ particle atomic number of element would increase by $1$ unit and mass number of element would remain unchanged.
So after emitting a ~ particle $_{82}X198$ would become $_{82}X198 = _{83}X198.$
The daughter nucleus is rep resented by $_bY^a$
$^{_bYa}= _{83}X^{198.}$
$a= 198$
$b= 83.$

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Question 45 Marks

Distinguish between $\alpha , \beta$ and $γ$ rays.

Answer

SI. no	α particles	$\beta$ particles	γ radiations
$1$	$\alpha $ particles are Helium nucleus 2He4	$\beta$ particles are like electgrons $_{-1}\beta^\circ$	$γ$ radiations are electromagnetic radiations.
$2$	$\alpha $ particles are positively charged.	$\beta$ particles are negatively charged.	$γ$ radiations have no charge.
$3$	the mass of each α particles is $4 a.m.u$	The mass of each $\beta$ particle is negligible.	$γ$ radiations have no mass.
$4$	α particles has velocity less than velocity of light i.e $1 x 10^7ms^{-1}.$	Velocity of $\beta$ particle is comparable to the velocity of light.	Velocity of $γ$ radiation is equal to the velocity of light.
$5$	Ionosation power of a particles is maximum.It is about $100$ times more than that of $\beta$ particles	Ionisation power of $\beta$ particles is about $100$ times more than that of $γ$ radiations	Ionisation power is least.
$6$	The penetrating power of a particle is least.	penetrating power of $\beta$ particles is less but $100$ times more than that of α particle.	$γ$ radiations have maximum penetration power. They are $100$ times more penetrating than $\beta$ paticles.
$7$	$\alpha$ particles are less deflected by electric and magnetic fields.	$\beta$ particles are more deflected by electric and magnetic field but in opposite direction.	$γ$ radiations are unaffected by electric and magnetic field.

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Question 55 Marks

Explain the use of radioactive in the field of medicine, agriculture and industry.

Answer

Uses of radioactivity in medical, agriculture and industry:
Uses in medical field:
(i) Rays from Radium produce satisfactorily improvement in skin diseases.
(ii) Radiation from $Co ^{60}$ is used in cancer treatment.
(iii) Radio $1^{131}$ is used to diagnose and treat thyroid disorders.
Uses in agriculture:
(i) Radioactive Phosphorus $P ^{32}$ is used in the study of metabolism.
(ii) Radioactive Sulphur $S ^{35}$ helps to study advantages and disadvantages of fungicides.
(iii) Pests and insects can be killed by Y-radiation.
Uses in industry:
(i) In manutacturing papers, plastic and $m \cdot e t a l$ sheets to control the thickness of the sheets.
(ii) Radioisotopes can be used to estimate the amount of wear in bearings.
(iii) Radioisotopes can be used to detect crack in welding, casting etc.

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Question 65 Marks

Radioactive substances were found to give off three types of rays. Name them. How do they
(a) React to the magnetic field?
(b) React to the electric field?
(c) Act when different thickness of lead sheets is placed in their path?

Answer

A radioactive source emits three types of radiations. These are a
radiations, β radiations and γ radiations.
(i) α particles are heavy in mass and have positive charge so they are less deflected by magnetic field. β particles are Iighter in mass and have negative charge so they are deflected mo re by magnetic field in opposite direction to a particle's deflection. γ radiations are charge less and mass less so they are not deflected by magnetic field.
(ii) a particles are heavy in mass and have positive charge so they are less deflected by electric field towards negative plate. β particles are Iighter in mass and have negative charge so they are deflected mo re by electric field towards positive plate. γ radiations are charge less and mass less so they are not deflected by electric field.
(iii) The penetrating power of a particle is least. They can't penetrate lead sheet very much. Penetrating power of β particles is less but 100 times mo re than that of a particle. So, it will penetrate lead sheet more than a particles. γ radiations have maximum penetration power. They are 100 times more penetrating than β particles. So, γ radiations wouId penetrate in lead sheet by larqest amount.

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Question 75 Marks

One isotopes of uranium has a mass number of $235$ and atomic number $92$.
(a) What is the number of electrons in a neutral atom of this isotope?
(b) How many protons are there in the nucleus of this isotope?
(c) For another isotope of Uranium state which one of the numbers ($238$ or $92$) changes?
(d) What is the number of protons in ${ }^{238} U$ ?

Answer

(a)Mass number of uranium $=235$
Atomic number of uranium $=92$
As atomic number of element gives number of proton and electrons while mass number of element gives number of protons + number of neutrons.
So, number of protons in uranium = atomic number of uranium $=92$.
(b) Number of electron in uranium = number of protons in uranium $=92$.
(c)The atoms of same elements having the same atomic number $Z$ but different mass number A are called isotopes.
So, for another isotope of uranium mass number $235$ changes.
(d)Number of protons in isotopes is same and as $U238$ is isotope of ${ }_{92} U ^{235}$. So, number of protons in $U ^{235}$ is also $92.$

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Question 85 Marks

What are the names of the three types of rays given off by a radioactive substance? Define the properties you know they possess. Why are the largest atoms radioactive?

Answer

A radioactive source emits three types of radiations. These are a
radiations, $\beta$ and $Y$ radiation.
$\alpha $ radiation
(i) a particles are He I iu m nucleus ${ }_2 He ^4$.
(ii) a particles are positively charged.
(iii) The mass of each a particle is $4 a . m . u$.
(iv) Ionization power of a particle is maximum. It is about 100 times more than that of $\beta$ particles.
(v) $\alpha$ particle has velocity less than the velocity of light i.e $1 \times 10^7 ms^{-1}$.
(vi) The penetrating power of a particle is least.
(vii) a particles are less deflected by electric and magnetic fields.
$\beta$ particles
(i) $\beta$ particles are like electrons ${ }_{-1} \beta^{\circ}$.
(ii) $\beta$ particles are negatively charged.
(iii) The mass of each $\beta$ particle is negligble.
(iv) Velocity of $\beta$ particle is comparable to the velocity of light.
(v) Ionization power of $\beta$ particle is about 100 times more than that of $Y$ radiations.
(vi) Penetrating power of $\beta$ particles is less but 100 times more than that of a particle.
(vii) $\beta$ particles are more deflected by electric and magnetic field but in opposite direction.
$Y$ radiations
(i) $Y$ radiations a re electromagnetic radiations.
(ii) $Y$ radiations have no charge.
(iii) $Y$ radiations have no mass.
(iv) Velocity of $Y$ radiation is equal to the velocity of light.
( v) Ionization power is least.
(vi) $Y$ radiations have maximum penetration power. They are $100$ times more penetrating than $\beta$ particles.
(vii) $Y$ radiations a re unaffected by electric and magnetic field.
Heavy nucleus undergo radioactivity because they are unstable.

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Question 95 Marks

What do you mean by background radiations? Name its sources. Is it possible for us to keep ourselves away from it?

Answer

The low temperature microwave radiation that arrives at the earth's surface from all directions of outer space is called background radiation.
Sources of background radiations are:
(a) Radiation from the sun.
(b) Rocks in the earth which contain traces of radioactive substances.
(c) Naturally occurring isotopes.
(d) Artificial radioisotopes.
No, it is not possible to keep ourselves away from these radiations.

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Question 105 Marks

What are the uses of radioactive isotopes in following?
(a) Medical field,
(b) Agriculture,
(c) Industries?

Answer

Radioactive isotopes are used in medical field
(i) Rays from Radium produce satisfactorily improvement in skin diseases.
(ii) Radiation from $Co ^{60}$ is used in cancer treatment.
(iii) Radio ${ }^{131}$ is used to diagnose and treat thyroid di so rde rs.
Radioactive isotopes are used in agriculture
(i) Radioactive Phosphorus $p ^{32}$ is used in the study of metabolism.
(ii) Radioactive Sulphur $S ^{35}$ helps to study advantages and disadvantages of fungicides.
(iii) Pests and insects can be killed by Y -rad iatio $n$.
Radioactive isotopes are used in ind us try.
(i) In manufacturing papers, plastic and metal sheets to control the thickness of the sheets.
(ii) Radioisotopes can be used to es ti mate the amount of wear in bearings.
(iii) Radioisotopes can be used to detect crack in welding, casting etc.

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