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Physics
WAEC / WASSCE 2012
Mechanics and Properties of Matter
Solution
Which of the following arrangements of radiations is in the order of decreasing penetrating power?
A
\(\alpha\), \(\beta\), \(\gamma\)
B
\(\alpha\), \(\gamma\), \(\beta\)
C
\(\gamma\), \(\beta\), \(\alpha\)
D
\(\beta\), \(\gamma\), \(\alpha\)
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
The alpha rays are the least penetrating, followed by beta rays, and gamma rays are the most penetrating.
in descending order \(\gamma, \beta, \alpha\)
Source: Myschool Past Questions Archive (Record #35646)
Physics
WAEC / WASSCE 2012
Mechanics and Properties of Matter
Solution
Which of the following radiations emitted in radioactive decay has momentum, a fairly high penetrating power and is deflected by a magnet?
A
alpha particles
B
beta particle
C
gamma radiation `
D
X-radiation
medium Difficulty
Verified Correct Answer: Option B
Physical Principles & Numerical Solution
\beta Particles are equivalent to electrons but arise from radioactive decay of unstable atoms. They are emitted with a continuous range of energies up to a maximum that is characteristic of each radionuclide. Electrons have a greater range and penetrating power, but much less ionizing potential compared with \alpha particles.
Beta particles are deflected by a magnetic field in an opposite direction to alpha particles confirming they must hold a charge opposite to alpha particles.
Source: Myschool Past Questions Archive (Record #35647)
Physics
WAEC / WASSCE 2012
Electricity and Magnetism
The magnetic relay is a device used for
A
timing in sports
B
storing magnetic field
C
readin the magnitude of magnetic flux
D
controlling another circuit carrying larger current
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 #35624)
Physics
WAEC / WASSCE 2012
Electricity and Magnetism
the core of a transformer is usually laminated in order to
A
reduce magnetic leakage
B
reduce eddy current
C
prevent vibration of the transformer
D
make magnetic reversal in the core much easier
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 #35626)
Physics
WAEC / WASSCE 2012
Mechanics and Properties of Matter
Which of the following modes is the most economical method of transmitting electrical power over long distances?
A
alternating current at low voltage and high current
B
alternating current at high voltage and high current
C
alternating current at high voltage and low current
D
direct current at low voltage and high current
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 #35629)
Physics
WAEC / WASSCE 2012
Electricity and Magnetism
Solution
An inductor is connected to a 24V, 50Hz mains supply. If the current through the inductor is 1.5A, calculate the inductance of the inductor (\(\pi = \frac{22}{7}\))
A
8.0 x 102H
B
7.5 x 10oH
C
1.6 x 10oH
D
5.1 x 10-2H
medium Difficulty
Verified Correct Answer: Option D
Physical Principles & Numerical Solution
\(X_L = \frac{V}{I} = \frac{24}{1.5} = 16\Omega\)
L = \(\frac{XL}{2 \pi f} = \frac{16}{2 \pi 50}\)
= 0.05H
Source: Myschool Past Questions Archive (Record #35635)
Physics
WAEC / WASSCE 2012
Electricity and Magnetism
Solution
In a R-C circuit
A
Irms leads Vrms by 60o
B
Irms slags Vrms by 60o
C
Vrms lags Irms by 90o
D
Vrms leads Irms by 90o
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
In an A.C circuit, the voltage(V\(_{rms}\) is completely in phase with the current for a resistor and lags the current by 90º for a capacitor(R - C)
Source: Myschool Past Questions Archive (Record #35638)
Physics
WAEC / WASSCE 2012
Electricity and Magnetism
Solution
Two capacitors, each of capacitance 2\(\mu\)F are connected in parallel. If the p.d across them is 120V, calculate the charge on each capacitor
A
6.0 x 10-5C
B
1.2 x 10-4C
C
2.4 x 10-4C
D
4.8 x 10-4C
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
C = \(C_1 + C_2 = 2 + 2 = 4 \mu F\)
but Q = CV
= 4 x 10\(^{-6}\) x 120
= 4.8 x 10\(^{-4}\)
\(\therefore\) Each of the capacitor has a charge of \(\frac{4.8 \times 10^{-4}}{2}\)
= 2.4 x 10\(^{-4}\) C
Source: Myschool Past Questions Archive (Record #35613)
Physics
WAEC / WASSCE 2012
Heat Energy & Temperature
Which of the following properties is an advantage of lead-acid accumulator over an alkaline accumulator?
A
possesses low internal resistance
B
can be recharges
C
has shorter life span
D
possesses high e.m.f
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 #35614)
Physics
WAEC / WASSCE 2012
Electricity and Magnetism
Solution
Six dry cells each of e.m.f. 2.0 and internal resistance of 1.0\(\Omega\) are connected in parallel across a load of 3.0\(\Omega\). Calculate the effective current in the circuit.
A
0.63A
B
0.50A
C
0.31A
D
0.22A
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
I = \(\frac{f}{n} = \frac{1}{6 - 2}\)
I = \(\frac{v}{R + r} = \frac{2}{3} + \frac{1}{6} = 0.63\)A
Source: Myschool Past Questions Archive (Record #35616)
Physics
WAEC / WASSCE 2012
Mechanics and Properties of Matter
Diagram
Solution
Two similar cells are used to light two similar lamps as illustrated in the diagrams above. In which of the circuit diagrams are the lamps brightest?
Attached Figure / Diagram
A
P
B
Q
C
R
D
S
medium Difficulty
Verified Correct Answer: Option B
Physical Principles & Numerical Solution
The determinant of the brightness of a bulb is the power (watts) of the circuit.
Recall that Power (P) = \(\frac{V^2}{R}\).
Since the resistance is to be used as a divisor, it means the smaller the resistance, the greater the power.
Source: Myschool Past Questions Archive (Record #35619)
Physics
WAEC / WASSCE 2012
Heat Energy & Temperature
Solution
You are provided with a potentiometer, an ammeter, a voltmeter, a standard resistor, and other necessary apparatus. Using the circuit diagram above as a guide carry out the following instructions.
Set up a circuit as illustrated in the diagram above.
Close the key, K.
Read and record the ammeter reading \(l_o\) and the voltmeter reading \(V_o\) when jockey J is not making contact with the potentiometer wire OQ.
Using J, make a contact with the potentiometer wire OQ at a point P such that OP = 1Ocm.
Read and record the current and the corresponding value of the voltage V.
Repeat the procedure for other values of OP= 20cm, 30cm, 40cm, 50cm, and 60cm.
Tabulate your readings.
Plot a graph with V on the vertical axis and I on the horizontal axis, starting both axes from the origin (0, 0).
Determine the slope, s, of the graph.
Determine the value of V when I = 0.
State two precautions taken to obtain accurate results.
(b) i. State two advantages of a lead-acid accumulator over a dry Leclanche cell.
ii. A cell of emf 2V and internal resistance of 1\(\Omega\) passes current through an external load of 9\(\Omega\). Calculate the potential drop across the cell.
A
5.8A
B
6.9A
C
30.0A
D
33.3A
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
S/N
OP(\(_{cm}\))
I(\(_{A}\))
V(\(_{v}\))
1
20.0
0.13
1.08
2
30.0
0.14
0.97
3
40.0
0.15
0.85
4
50.0
0.16
0.74
5
60.0
0.17
0.60
Slope, s = \(\frac{y_{2} - y_{1}}{x_{2} - x _{1}} = \frac{0.85 - 0.30}{0.20 - 0.5}\)
\(\frac{0.55}{0.05}\)
= 11
When I = o
V = 3.15v
Precautions; i
- ensured that the key was open whenever the circuit was not in use so as to avoid the cells being run down.
- ensured there was no zero error in the ammeter and the voltmeter by making necessary adjustments before taking my readings.
- ensured that the jockey did not scrap the potentiometer wire.
- ensured that the electrical wires were tightly connected to the terminals in order to avoid current fluctuations.
(b)i.
Lead-acid accumulator
Leclanche cell
(i). It has the capacity to supply large current for a long time
(ii). It can be charged
It has no such capacity
It cannot be recharged
ii. e.m.f = 2V
r = 1\(\Omega\) (internal resistance)
R = 9\(\Omega\) (external resistance)
Calculate the potential drop across the cell.
By formula;
E = I(R +r)
2 = I(9 + 1)
2 = 101
I = \(\frac{2}{10}\) = 0.2A
Therefore, the p.d drop across the cell is Ir.
= 0.2 x 1 = 0.2V
Source: Official Exam / Past Question Archive
Physics
WAEC / WASSCE 2012
Waves and Optics
Solution
A ray of light is incident on an air-glass boundary at an angle \(\theta\). If the angle between the partially reflected ray and the refracted ray is 90^\circ, calculate \(\theta\), given that the refractive index of glass is 1.50.
medium Difficulty
Verified Correct Answer: Option
Physical Principles & Numerical Solution
n = \(\frac{sin i}{sin r}\)
1.5 = \(\frac{sin \theta}{sin(190 - \theta)} = \frac{sin \theta}{cos theta} = \tan \theta\)
Hence, 0 = tan\(^{-1}\) 1.5 = 56.31\(^o\)
Source: Myschool Past Questions Archive (Record #53207)
Physics
WAEC / WASSCE 2012
Heat Energy & Temperature
Diagram
Solution
In the diagram illustrated, a body of mass m slides on an inclined plane. Show that the coefficient M\(_g\) of friction between the surfaces in contact is tan \(\theta\).
Attached Figure / Diagram
medium Difficulty
Verified Correct Answer: Option
Physical Principles & Numerical Solution
(1) If F = uniform speed of body
\(\mu = \frac{F}{R} = \frac{Mg sin \theta}{Mg cos \theta} = tan \theta\)
Source: Myschool Past Questions Archive (Record #53210)
Physics
WAEC / WASSCE 2012
Electricity and Magnetism
Solution
(a) Explain the term electrodes in electric cells.
b) An electric current passing through an electrolyte for 2 minutes deposited 200 g of a substance. If the electrochemical equivalent of the substance is 8.33 x 10\(^{-4}\)g C\(^{-1}\), calculate the current passed.
medium Difficulty
Verified Correct Answer: Option
Physical Principles & Numerical Solution
(a) An electrode is a conductor through which electrons flow into and out of the electric cell.
(b) I = \(\frac{M}{zt} = \frac{200}{8.33 \times 10^{-4} \times 60 \times 2}\)
Source: Myschool Past Questions Archive (Record #53212)