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Physics
WAEC / WASSCE 1998
Modern Physics and Nuclear Physics
Solution
A radioactive nuclide of proton number X emits a \(\beta\)-particle to form a new nuclide to proton number Y. The correct equation relating X and Y is
A
X = Y - 1
B
X = Y + 1
C
X = 1 - Y
D
X = \(\frac{1}{y}\)
E
X = Y
medium Difficulty
Verified Correct Answer: Option B
Physical Principles & Numerical Solution
There is an increase in proton number by one in a beta-decay.
Source: Myschool Past Questions Archive (Record #33698)
Physics
WAEC / WASSCE 1998
Modern Physics and Nuclear Physics
Solution
Two radioactive elements X and Y have half-lives of 100 and 50 years respectively. Samples of X and Y initially contain equal number of atoms. What is the ratio of the number of the remaining atoms of X to that of Y after 200 years?
A
4:1
B
3:1
C
1:1
D
1:2
E
1:4
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
Fraction remaining of X = (\(\frac{1}{2}\))\(^{\frac{t}{T_{\frac{1}{2}}}}\)
BUT \(\frac{t}{T_{\frac{1}{2}}}\) = \(\frac{200}{100}\) = 2
= (\(\frac{1}{2})^2\) = \(\frac{1}{4}\)
Fraction remaining of Y = (\(\frac{1}{2}\))\(^{\frac{t}{T_{\frac{1}{2}}}}\)
BUT \(\frac{t}{T_{\frac{1}{2}}}\) = \(\frac{200}{50}\) = 4
= (\(\frac{1}{2})^4\) = \(\frac{1}{16}\)
the ratio of the remaining atoms of X to Y = \(\frac{X}{Y}\) = \(\frac{\frac{1}{4}}{\frac{1}{16}}\) = \(\frac{1}{4}\) x \(\frac{16}{1}\) = 4
Therefore, the ratio of the number of remaining atoms of X to that of Y after 200 years is 4:1
Source: Myschool Past Questions Archive (Record #33700)
Physics
WAEC / WASSCE 1997
Modern Physics and Nuclear Physics
Solution
The half-life of a radioactive material is 6hrs. What quantity of 1kg of the material would decay in 24 hours?
A
\(\frac{15}{16}\)kg
B
\(\frac{1}{2}\)kg
C
\(\frac{1}{4}\)kg
D
\(\frac{1}{8}\)kg
E
\(\frac{1}{6}\)kg
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
To determine the quantity of a 1 kg radioactive material that decays in 24 hours, given a half-life of 6 hours:
The number of half-lives in 24 hours is:
\(\text{Number of half-lives} = \frac{24 \text{ hours}}{6 \text{ hours/half-life}} = 4\)
The remaining quantity after 4 half-lives is:
\(\text{Remaining quantity} = 1 \text{ kg} \times \left( \frac{1}{2} \right)^4 = 1 \text{ kg} \times \frac{1}{16} = \frac{1}{16} \text{ kg}\)
The decayed quantity is: \(\text{Decayed quantity} = 1 \text{ kg} - \frac{1}{16} \text{ kg} = \frac{15}{16} \text{ kg}\)
Thus, the quantity that decayed in 24 hours is: \(\frac{15}{16} \text{ kg}\)
Source: Myschool Past Questions Archive (Record #26312)
Physics
WAEC / WASSCE 1996
Modern Physics and Nuclear Physics
Solution
Which of the following particles/rays do not originate from the nucleus of an atom?
A
Alpha particles
B
Beta particles
C
Neutrons
D
Gamma rays
E
X-rays
medium Difficulty
Verified Correct Answer: Option E
Physical Principles & Numerical Solution
All of the options above are emitted by the nucleus except X-rays that are emitted by electrons.
Source: Myschool Past Questions Archive (Record #25257)
Physics
WAEC / WASSCE 1996
Modern Physics and Nuclear Physics
Solution
The count rate of an alpha-particle source is 400 per minute. If the half-life of the source is 5 days, what would be the count rate per minute after 15 days?
A
20
B
25
C
50
D
200
E
400
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
Initial count rate N\(_o\) = 400 per minute, Half-life\(T_{\frac{1}{2}}\) = 5 days, T = 15days, N (count after 15 days) = ?
Using: N = N\(_o\)(\(\frac{1}{2}\))\(^{\frac{T}{T_{\frac{1}{2}}}}\)
N = 400 x (\(\frac{1}{2}\))\(^{\frac{15}{5}}\)
N = 400 x \(\frac{1}{2}\)\(^3\) = 400 x \(\frac{1}{8}\) = \(\frac{400}{8}\) = 50.
Source: Myschool Past Questions Archive (Record #25258)
Physics
WAEC / WASSCE 1996
Modern Physics and Nuclear Physics
What is the decay constant of a radioactive element whose half-life is 3 seconds
A
0.132s-1
B
0.23s-1
C
0.347s-1
D
0.693s-1
E
0.924s-1
medium Difficulty
Verified Correct Answer: Option B
Physical Principles & Numerical Solution
No expanded working has been attached for this question yet. The verified answer is Option B.
Source: Myschool Past Questions Archive (Record #25252)
Physics
WAEC / WASSCE 1995
Modern Physics and Nuclear Physics
A radioactive nuclide of mass 6.09 has a half-life of 8 days. Calculate the time during which 5.25g of the nuclide would have decayed
A
1 day
B
2 days
C
8 days
D
24 days
E
42 days.
medium Difficulty
Verified Correct Answer: Option D
Physical Principles & Numerical Solution
No expanded working has been attached for this question yet. The verified answer is Option D.
Source: Myschool Past Questions Archive (Record #25104)
Physics
WAEC / WASSCE 1995
Modern Physics and Nuclear Physics
Which of the following are emitted from a radioactive substance without altering either the nucleon number or the proton number of the substance?
A
Protons
B
Neutrons
C
Gamma rays
D
Beta particles
E
Alpha particles
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
No expanded working has been attached for this question yet. The verified answer is Option C.
Source: Myschool Past Questions Archive (Record #25106)
Physics
WAEC / WASSCE 1995
Modern Physics and Nuclear Physics
Which of the following is used for shielding radioactive fall-outs?
A
Plastic
B
Wood
C
Textile
D
Aluminium
E
Lead
medium Difficulty
Verified Correct Answer: Option E
Physical Principles & Numerical Solution
No expanded working has been attached for this question yet. The verified answer is Option E.
Source: Myschool Past Questions Archive (Record #25109)
Physics
UTME / JAMB 1995
Modern Physics and Nuclear Physics
The half-life of a radio-active element is 9 days, what fraction of atoms has decayed in 36 days?
A
\( \frac{1}{16} \)
B
\( \frac{1}{4} \)
C
\( \frac{1}{2} \)
D
\( \frac{15}{16} \)
medium Difficulty
Verified Correct Answer: Option D
Physical Principles & Numerical Solution
No expanded working has been attached for this question yet. The verified answer is Option D.
Source: Myschool Past Questions Archive (Record #41542)
Physics
WAEC / WASSCE 1994
Modern Physics and Nuclear Physics
Solution
Beta particles are
A
electrons
B
protons
C
neutrons
D
helium nuclei
E
tritium nuclei
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
Beta particles are equivalent to electrons but arise from the radioactive decay of unstable atoms. They are emitted with a continuous range of energies up to a maximum that is characteristic of each radionuclide.
Source: Myschool Past Questions Archive (Record #26268)
Physics
WAEC / WASSCE 1994
Modern Physics and Nuclear Physics
Solution
In 24 days a radioactive isotope decreases in mass from 64g to 2g. What is the half life of the radioactive material
A
0.75 days
B
2.58 days
C
4 days
D
4.80 days
E
6 days
medium Difficulty
Verified Correct Answer: Option D
Physical Principles & Numerical Solution
64g → 32g → 16g → 8g → 4g → 2g
Half life time= 24/5 = 4.8 days
Source: Myschool Past Questions Archive (Record #26272)
Physics
UTME / JAMB 1994
Modern Physics and Nuclear Physics
Solution
A certain radioisotope of \(^{235}_{92}U\) emits four alpha particles and three beta particles. The mass number and the atomic number of the resulting elements respectively are
A
219 and 87
B
84 and 223
C
223 and 87
D
219 and 81
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
\(^{235}_{92}U\) \(\to\) 4\((^{4}_{2}\alpha)\) + 3\((^{0}_{-1}e)\) + \(^{b}_{a}y\)
a + (4 + 2) + (3x - 1) = 92 \(\Rightarrow\) a = 87
b + (4 x 4) + (3 x 0) = 235 \(\Rightarrow\) b = 219
\(^{b}_{a}Y\) = \(^{219}_{87}Y\)
Source: Myschool Past Questions Archive (Record #27936)
Physics
WAEC / WASSCE 1993
Modern Physics and Nuclear Physics
Solution
A radioactive substance has a half-life of 20 hours. What fraction of the original radioactive nuclide will remain after 80 hours?
A
1/32
B
\(\frac{1}{16}\)
C
\(\frac{1}{8}\)
D
\(\frac{1}{4}\)
E
\(\frac{1}{2}\)
medium Difficulty
Verified Correct Answer: Option B
Physical Principles & Numerical Solution
Fraction remaining = (\(\frac{1}{2}\))\(^{\frac{t}{T_{\frac{1}{2}}}}\)
BUT \(\frac{t}{T_{\frac{1}{2}}}\) = \(\frac{80}{20}\) = 4
Fraction remaining = (\(\frac{1}{2})^4\) = \(\frac{1}{16}\)
Source: Myschool Past Questions Archive (Record #25047)
Physics
WAEC / WASSCE 1993
Modern Physics and Nuclear Physics
Which of the following are emitted from a radioactive substance without altering either the nucleon number or the proton number of the substance?
A
Gamma rays
B
Alpha particles
C
Beta particles
D
Protons
E
Neutrons
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
No expanded working has been attached for this question yet. The verified answer is Option A.
Source: Myschool Past Questions Archive (Record #25052)