Saturday, May 2, 2015

Physics 9702 Doubts | Help Page 129

  • Physics 9702 Doubts | Help Page 129



Question 647: [Radioactive decay]
Nucleus of bohrium xyBh decays to mendelevium 255101Md by a sequence of three α-particle emissions.

How many neutrons are there in a nucleus of xyBh?
A 267                          B 261                          C 160                          D 154

Reference: Past Exam Paper – June 2002 Paper 1 Q40



Solution 647:
Answer: C.
An α-particle is a helium nucleus and thus, is 42α.

Since 3 α-particles are emitted,
xyBh     - - - >   255101Md          +          3 42α
Value of x = 255 + 3(4) = 267
Value of y = 101 + 3(2) = 107

Number of neutrons = x – y = 267 – 107 = 160










Question 648: [Nuclear Physics]
A thin gold foil is bombarded with α-particles as shown.

Results of this experiment provide information about the
A binding energy of a gold nucleus.
B energy levels of electrons in gold atoms.
C size of a gold nucleus.
D structure of a gold nucleus.

Reference: Past Exam Paper – June 2004 Paper 1 Q39



Solution 648:
Answer: C.
This experiment (bombardment of a thin gold foil with α-particles) tells us about the size of the nucleus, not its structure.

Most of the α-particles pass through the foil. This indicates that the gold atom is mostly empty spaced. That is, the size of the nucleus is much smaller than that of the atom.

A few of the α-particles are deflected at very large angles – this tells that something massive is present in the atom and this is the nucleus as we know.

A few of the α-particles are reflected back. This tells us that the nucleus is positively charged as it repels the α-particles which are themselves positively charged.

But none of these deductions tells us about the structure of the gold nucleus – that is, that the gold nucleus contains protons and neutrons.










Question 649: [Radioactive decay]
Student conducts an experiment using an α-particle source.
When considering safety precautions, what can be assumed to be maximum range of
α-particles in air?
A between 0 and 5 mm
B between 5 mm and 200 mm
C between 200 mm and 500 mm
D between 500 mm and 1000 mm

Reference: Past Exam Paper – June 2005 Paper 1 Q39




Solution 649:
Answer: B.
In this question, we need to be careful of the unit used for the range. The values are given in mm.

The range of α-particles in air is about 0 – 5cm.

Choice A is in mm, so it is incorrect.
Choice D is almost completely out of the range while choice C neglects a significant portion of the range (0 – 199mm is neglected).









Question 650: [Nuclear Physics]
Which conclusion can be drawn from the results of the experiment showing scattering of α-particles by gold foil?
A Electrons orbit the atomic nucleus in well-defined paths.
B Nuclei of different isotopes contain different numbers of neutrons.
C The atomic nucleus contains protons and neutrons.
D The nucleus is very small compared with the size of the atom.

Reference: Past Exam Paper – November 2008 Paper 1 Q38



Solution 650:
Answer: D.
Most of the alpha particles pass through the gold foil. This indicates that the nucleus is very small compared with the size of the atom.




2 comments:

  1. Here are the remaining questions for now:

    22/O/N/10 Q.4(b)(ii)

    21/O/N/11 Q.5(b)

    23/O/N/11 Q.6(c)

    23/M/J/12 Q.2(c)

    21/O/N/12 Q.6(c)

    22/O/N/12 Q.3(b)

    23/O/N/12 Q.1(e)

    21/M/J/13 Q.6(c)(d)

    22/O/N/13 Q.3(c)(ii)

    23/O/N/13 Q.5(c)

    ReplyDelete
    Replies
    1. For 22/O/N/10 Q.4(b)(ii)
      http://physics-ref.blogspot.com/2014/09/9702-november-2010-paper-22-worked.html

      Delete

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