Chapter Unit - 6 : Modern Physics - Frank Solutions for Class 10 Physics ICSE

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Chapter Unit - 6 - Modern Physics Excercise 283

Question 1

Make the correct choices in the following:
(a) In one atom of copper (mass number 63, atomic number 29) there are
(i) 63 protons and 29 neutrons.
(ii) 63 protons and 29 electrons.
(iii) 29 protons and 29 neutrons.
(iv) 29 protons and 29 electrons.
(v) 29 protons and 63 neutrons.

Solution 1

(a) Mass number of copper = 63
Atomic number of copper = 29
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 copper = atomic number of copper = 29.
Number of electron in copper = number of protons in copper =29.
Number of neutrons = mass number atomic number = 63 29 =34.
So answer is (iii) as copper contains 29 protons and 29 electrons.

Chapter 6 - Modern Physics Excercise 284

Question 1
Define the term radioactivity. Of the three normally occurring radioactive radiations:
(a) Which has a positive charge?
(b) Which is most penetrating?
(c) Which has no electric charge?
Solution 1
Question 2
Which of the following statements are correct?
(a) Electrons have
 (i) No mass,
(ii) A mass less than that of a proton,
(iii) A mass equal to that of a helium atom,
(iv) Mass greater than that of a neutron.
(b) Neutrons have
(i) A double positive charge,
(ii) A single positive charge,
(iii) A negative charge,
(iv) No electric charge.
Solution 2
(a)    Electron has        (ii) a mass less than that of a proton.
(b)    Neutrons have     (iv) no electric charge.
Question 3
Draw a diagram of a simple atom showing the nucleus and electrons. In this atom:
(a) What type of charge will there be on the nucleus?
(b) What is the value of this charge?
Solution 3
Question 4
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?
Solution 4
Question 5

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 238U?

Solution 5
(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 92U235. So, number of protons in U235 is also 92.
Question 6
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?
Solution 6
Question 7
Chlorine has an atomic number 17 in the form of isotope, one of atomic weight 35 and the other atomic weight 37. What do you understand by an isotope? Name two other elements which have isotopes.
Solution 7
The atoms of same elements having the same atomic number Z but different mass number a are called isotopes. Hydrogen have 3 isotopes protium 1H1, deuterium 1H2, tritium 1H3.
Question 8
(a) What is the meaning of mass number?
(b) What do you mean by atomic number?
(c) In what way are these numbers related to the isotopes of an element?
(d) Explain the use of radioactive in the field of medicine, agriculture and industry.
Solution 8

Question 9
Solution 9
Question 10
State three precautions taken while handling radioactive substances.
Solution 10
Following precautions should be taken while handling the radioactive substances.
(i)    The sources should only be handled by the forceps provided and never touched by hand.
(ii)    They should never be pointed towards a person.
(iii)    Food should not be taken where the sources are being used, as it may be contaminated.
(iv)    Never smoke near a radioactive source
Question 11

What do you understand by radioactive decay? An isotope of Uraniumbegin mathsize 12px style straight U presubscript 92 presuperscript 238
end style is radioactive and changes into Thorium 92 by the emission of an alpha particle. Write a symbolic equation for this decay process.

Solution 11

Question 12

The element begin mathsize 12px style Na presubscript 11 presuperscript 24 end style changes to magnesium by the emission of a beta particle. Write down the symbolic equation for the beta emission.

Solution 12

Question 13
(a) What do you understand by thermionic emission?
(b) What are the factors on which thernionic emission depends?
Solution 13
(a)    When certain metals are heated to a high temperature, they emit thermions (electrons)  and the phenomenon is called thermionic emission.
(b)    Thermionic emission of electrons from a heated surface depends upon:
(i)    Work function of the material.
(ii)    Melting point of the material.
Question 14
(a) Draw a neat and labeled diagram of cathode ray tube.
(b) Name two applications of cathode ray tube.
Solution 14
(a)
(b)    Uses of cathode ray tubes are:
(i)     Cathode ray tubes are used in science research laboratories by scientist for converting electrical signals into visual signals and television tubes.
(ii)     Cathode ray tubes are used by doctors for converting electrical impulses corresponding to heart beats into visual signals in ECG, EEG etc.
Question 15
(a) Define radioactivity.
(b) Name three radioactive isotopes.
Solution 15
Question 16
Solution 16
Question 17
State some of the safety precautions that we have to taken when we are exposed to some of the radiations or when we are handling some of the radioactive substances.
Solution 17
Following precautions should be taken while handling the radioactive substances.
(i)    The sources should only be handled by the forceps provided and never touched by hand.
(ii)    They should never be pointed towards a person.
(iii)    Food should not be taken where the sources are being used, as it may be contaminated.
(iv)    Never smoke near a radioactive source.
Question 18
What are the uses of radioactive isotopes in following?
(a) Medical field,
(b) Agriculture,
(c) Industries?
Solution 18
Question 19
What do you mean by background radiations? Name its sources. Is it possible for us to keep ourselves away from it?
Solution 19
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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