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Physics
WAEC / WASSCE 2018
Waves, Sound & Vibrations
Solution
(a) Define dffraction.
(b)(i) Explain critical angle. The diagram here illustrates a ray of light passing through a rectangular transparent plastic block \(\alpha\) Determine the value of the critical angle. \(\beta\) Calculate the refractive index of the block.
(c) A pipe closed at one end has fundamental frequency of 200Hz. The frequency of the first overtone of the closed pipe is equal to the frequency of the first overtone of an open pipe. Calculate the:
(i) fundamental frequency of the open pipe;
(ii) length of the closed pipe;
(iii) length of the open pipe. [Speed of sound in air = 330 ms\(^{-1}\)]
medium Difficulty
Verified Correct Answer: Option
Physical Principles & Numerical Solution
(a) Diffraction is the bending or spreading of a wave round an obstacle or as it passes through an opening.
(b) (i) Critical angle is the angle of incidence in the denser medium when an angle of refraction in the lens dense medium is 90^\circ.
(ii) (\(\alpha\))Critical angle = 90^\circ -.44^\circ = 46^\circ
(\(\beta\))n = \(\frac{1}{sin c} = \frac{1}{\sin 46^o}\) = 1.39
(c) (i) Closed Pipe
1st Overtone = 3f\(_o\) = 3 x 200 = 600Hz
Open Pipe
All harmonics are possible overtone = 2f\(_o\)
2f\(_o\) = 600
f\(_o\) = 300Hz
(ii) Closed Pipe
f\(_o\) = \(\frac{v}{4l}\)
l = \(\frac{v}{4f_o}\)
\(\frac{330}{4 \times 200}\)
= 0.412m
Open Pipe
\(f_1\) = \(\frac{v}{l}\)
600 = \(\frac{300}{l}\)
l = 0.55m
or
\(f_1\) = \(\frac{v}{2l}\)
300 = \(\frac{300}{2 \times l}\)
l = \(\frac{330}{600}\)
= 0.55m
Source: Myschool Past Questions Archive (Record #52872)
Physics
WAEC / WASSCE 2018
Current Electricity & Electric Circuits
Solution
(a) Define:
(i) reactance;
(ii) impedance in an a.c.
The diagram here illustrates an a.c. generator. When the coil is rotated, an e.m.f is induced in the coil.
(i) Explain why an e.m.f. is induced.
(ii) State the purpose of the slip-rings.
(iii) Name and state the law used to determine the direction of the induced current.
(iv) State two ways to increase the induced e.m.f.
(c) A lamp is rated 12 V. 6 W. Calculate the amount of energy transformed by the lamp in 5 minutes.
medium Difficulty
Verified Correct Answer: Option
Physical Principles & Numerical Solution
(a)(i) Reactance is the opposition to the flow of a.c offered by a capacitor or an inductor or both.
(ii) Impedance is the overall opposition of a mixed circuit containing a resistor, an inductor and/or a capacitor.
(b) (i) Emf is induced because the coil rotates at a steady speed about a fixed axis in the magnetic field of the elctromagnet, it cuts through the magnetic lines of force.
(ii) The direction of current is reversed in each half of the rotation of the coil.
(iii) The law used to determine the direction of the induced current is Lenz's law. It states that the direction of the induced current is such as to oppose the change producing it.
(iv) The induced e.m.f can be increased by any two of the following: increased speed of rotation, efficient core design, increased number of turns in the coil and increased area of coil.
(c) E = Power x Time
= 6 x 5 x 60
=1800J
Source: Myschool Past Questions Archive (Record #52873)
Physics
WAEC / WASSCE 2018
Atomic, Quantum, Nuclear Physics & Electronics
Solution
(a) Define binding energy in an atom.
(b) List three evidence to support the claim that X-rays are electromagnetic waves.
(c) List three peaceful uses of nuclear energy.
(d) Light of wavelength 4.5 x 10\(^{-7}\) in is incident on a metal resulting in the emission of photo electrons. If the work function of the metal is 3.0 x 10\(^{-9}\) J, calculate the:
(i) frequency of the incident light;
(ii) energy of the incident light;
(iii) energy of the photoelectrons. [Speed of light = 3.0 x 10\(^8\) ms\(^{-1}\), h = 6.6 x 10\(^{-34}\) Js]
medium Difficulty
Verified Correct Answer: Option
Physical Principles & Numerical Solution
(a) Binding energy is the minimum energy required to seperate the nucleus of an atom.
(b) Three evidences in support of the claim that x -rays are electromagnetic waves are:
(i) They can be polarized.
(ii) They can travel through a vacuum.
(iii) They travel with the speed of light.
(iv) They are not affected by electric field.
(v) They are not affected by magnetic field.
(c) Three peaceful uses of nuclear energy are:
(i) It is used in the treatment of tumour.
(ii) It is used to power submarines.
(iii) It is used to generate electricity.
(d) (1) c = f\(\lambda\) or f = \(\frac{c}{\lambda}\)
f = \(\frac{3.0 \times 10^8}{4.5 \times 10^{-7}}\)
f = 6.67 x10\(^{14}\)Hz
(ii) E = hf
= 6.67 x10\(^{-34}\) x 6.67 x10\(^{14}\)J
= 4.4 x10\(^{-19}\)J
(iii) K.E = E- W
= 4.4 x 10\(^{-19}\)
=1.4 x 10\(^{-19}\) - 3.0 x 10\(^{-19}\)
=1.4 x 10\(^{-19}\)J
Source: Myschool Past Questions Archive (Record #52874)
Physics
WAEC / WASSCE 2018
Current Electricity & Electric Circuits
Solution
You are provided with an ammeter, a resistor, key, metre bridge, and other necessary apparatus.
i. Connect a circuit as shown in the diagram above.
ii. Close the key and use the jockey to make contact with AB at N such that AN = d = 25cm
iii. Read and record the ammeter reading.
iv. Evaluate 1\(^{-1}\).
v. Repeat the procedures for values of d = 35cmm, 50cm, 65cm and 80cm. In each case, record I and determine 1\(^{-1}\)
vi. Tabulate your results.
vii. Plot a graph with log on the vertical axis and d on the horizontal axis.
viii. Determine the slope, s of the graph.
ix. State two precautions taken to obtain accurate results.
(b)i. Use your graph to determine the value of d = l = 1.5A.
ii. State two factors that affect the resistance of a wire.
A
0.5
B
0.8
C
1.2
D
1.5
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
S/N
d(cm)
I(A)
I\(^{1}\)(A\(^{-1}\))
Log I\(^{-1}\)
1
25
0.65
1.54
0.19
2
35
0.55
1.82
0.26
3
50
0.44
2.50
0.40
4
65
0.30
3.33
0.52
5
80
0.23
4.35
0.64
vii. Scale: 2cm to 10 units on x-axis
2cm to 0.1 unit on y-axis
viii. Slopes(s) = \(\frac{x_{2} - x_{1}}{y_{2} - y_{1}}\)
= \(\frac{80 -25}{0.64 - 0.20}\)
= \(\frac{55}{0.44}\)
= 125
(ix) Precautions
(a) Key opened in between reading or keys opened when readings were not taken
(b) Tight connections ensured
(c) Avoided parallax error when taking reading on ammeter or metre rule
(d) Repeated readings shown
(e) Avoided zero error on ammeter or metre rule
(f) Clean terminals ensured.
(b)i. 1\(^{-1}\) = \(\frac{1}{1.5}\)
= 0.67
Log(1\(^{-1}\)) =-0.174
ii. Factors affecting the resistance of a wire
- Length of wire
- Cross-sectional area/ thickness/ diameter/ radius of wire
- Resistivity or nature of wire
- Temperature.
Source: Official Exam / Past Question Archive
Physics
WAEC / WASSCE 2018
Circular Motion, Gravitation & Simple Harmonic Motion
Diagram
Solution
You are provided with a pendulum bob, a metre rule, a stopwatch, a retort stand with clamp, and other necessary apparatus.
i. Suspend the pendulum bob from the clamp as illustrated in the diagram.
ii. Adjust the pendulum such that AC=L= 90 cm
iii. Displace the pendulum bob slightly such that it oscillates in a vertical plane.
iv. Measure and record the time t for 20 complete oscillations.
v. Evaluate T and \(\sqrt L\)
vi.Repeat the procedure for four others values of L= 80 cm,70 cm, 60 cm, and 50cm.
vii. Tabulate your readings
viii. Plot a graph with T on the vertical axis and \(\sqrt L\) on the horizontal axis.
ix. Determine the slope, s, of the graph.
x. Evaluate g= \(\frac{4\pi^{2}}{5^{2}}\)
xi. State two precautions taken to ensure accurate results.
(b) i. Determine from your graph, the period of the pendulum for L= 75 cm.
ii. A simple pendulum bob is set into simple harmonic motion. Sketch a diagram of the setup and indicate on it; the positions of:
(a) maximum velocity.
(b) maximum acceleration of the bob
Attached Figure / Diagram
medium Difficulty
Verified Correct Answer: Option
Physical Principles & Numerical Solution
S/N
L(cm)
t(s)
T = \(\overline{20}\)(S)
\(\sqrt L\)
1
90
38
1.90
9.49
2
80
36
1.80
8.94
3
70
34
1.70
8.37
4
60
32
1.50
7.73
5
50
30
1.50
7.07
viii. Scale: 2cm rep 0.05 unit on y-axis
2cm rep 1.0 unit on x-axis
ix. Slopes(s) = \(\frac{X_2 - X_1}{Y_2 - Y_1}\)
= (\(\frac{9.9 - 5.7}{2.0 - 1.25}\))
= \(\frac{4.2}{0.75}\)
= 5.6cm
x. Evaluate g = \(\frac{4\pi{^2}}{5^{2}}\)
= \(\frac{4(3.143)^{2}}{(5.6)^{2}}\)
= \(\frac{9.878}{31.36}\)
= 0.315
xi. Precuations:
i. Avoided zero error on stop clock/ metre rule.
ii. Avoided draught.
iii. Avoided conical oscillation
iv. Ensured that support was rigid or firm
v. Ensured bob/pendulum was free from table.
(b)i. \(\sqrt{75cm}\) = 8.66
ii.
Source: Myschool Past Questions Archive (Record #59880)
Chemistry
WAEC / WASSCE 2018
Oxidation, Reduction & Redox Reactions
Which of the following equations represents a redox reaction?
A
\(HNO_{{3}{(aq)}} + NaOH_{(aq)} \to NaNO_{{3}{(aq)}} + H_{2}O_{(l)}\)
B
\(AgNO_{{3}{(aq)}}+KCl_{(aq)} \to AgCl_{(s)}+KNO_{{3}{(aq)}}\)
C
\(CaCO_{{3}{(s)}} \to CaO_{(s)} + CO_{{2}{(g)}}\)
D
\(2H_{2}S_{(s)} + SO_{{2}{(g)}} \to 2HO_{2} + 3S_{(g)}\)
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option D.
Source: Myschool Past Questions Archive (Record #48961)
Chemistry
WAEC / WASSCE 2018
Nature of Matter & Separation Techniques
Solution
The process of extraction of iron from its ore is
A
decomposition
B
oxidation
C
reduction
D
sublimation
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
The Iron is to to be gotten by the removal of oxygen from its ore, and this is called a reduction reaction.
Source: Myschool Past Questions Archive (Record #48963)
Chemistry
WAEC / WASSCE 2018
Water, Solutions & Solubility
Solution
What is the solubility of a salt if 0.4g of it is obtained on evaporating 200\(cm^{3}\) of its saturated solution to dryness?
A
0.08\(gdm^{-3}\)
B
2.00\(gdm^{-3}\)
C
8.00\(gdm^{-3}\)
D
80.00\(gdm^{-3}\)
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
1000\(cm^{3}\) = 1\(dm^{3}\)
200\(cm^{3}\) = 0.2\(dm^{3}\)
⇒ 0.2\(dm^{3}\) contains 0.4g
hence, solubility of the salt which is the amount of the salt dissolvable in 1\(dm^{3}\) is
\(\frac{0.4g}{0.2dm^{3}} = 2.0gdm^{-3}\)
Source: Myschool Past Questions Archive (Record #48965)
Chemistry
WAEC / WASSCE 2018
Acids, Bases, pH & Salts
Solution
An acidic salt has
A
double anions in its aqueous solution
B
a single cation in its aqueous solution
C
hydrogen ions in its aqueous solution
D
hydrogen atoms in its aqueous solution
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
Acid salts are salts whose aqueous solutions are acidic in character, implying that their aqueous solutions possess hydrogen ions.
Source: Myschool Past Questions Archive (Record #48966)
Chemistry
WAEC / WASSCE 2018
Chemical Energetics & Thermochemistry
Solution
A reaction is endothermic if the
A
reaction vessel feels cool during the reaction
B
enthalpy change is negative
C
bond forming energy exceeds bond breaking energy
D
heat of formation of reactants exceeds heat of formation of products
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
Endothermic reactions absorb heat from their surroundings during the reaction process. This means that in the course of the reaction the vessel being used in the reaction will be cool in the process.
Source: Myschool Past Questions Archive (Record #48967)
Chemistry
WAEC / WASSCE 2018
Organic Chemistry I: Hydrocarbons & Crude Oil
Solution
Which of the following raw materials is used in the plastic industry?
A
Ethene
B
Methane
C
Sulphur
D
Hydrogen
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
Ethene is the most important organic chemical, by weight, that is manufactured. It is an important raw material for the production of plastics and antifreeze solutions as well as solvents.
Source: Myschool Past Questions Archive (Record #48956)
Chemistry
WAEC / WASSCE 2018
Organic Chemistry I: Hydrocarbons & Crude Oil
Solution
Which of the following organic compounds can undergo both addition and substitution reactions?
A
Pentane
B
Benzene
C
Propane
D
Hexane
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
An example of benzene addition reaction is the formation of cyclohexane by a mix of benzene vapour and hydrogen passed over nickel catalyst; while chlorobenzene is formed by substitution reaction.
Source: Myschool Past Questions Archive (Record #48957)
Chemistry
WAEC / WASSCE 2018
Chemical Bonding & Intermolecular Forces
Solution
In which of the following compounds does hydrogen form ionic compounds?
A
C\(H_4\)
B
HCl
C
N\(H_3\)
D
NaH
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
The bonding between a non-metal and a metal is an ionic bonding. In metal hydrides, Hydrogen takes on the ionic charge of -1, hence forming an ionic bond with the metals.
Source: Myschool Past Questions Archive (Record #48969)
Chemistry
WAEC / WASSCE 2018
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
An organic compound has the empirical formula \(CH_{2}\). If its molar mass is 42\(gmol^{-1}\), what is its molecular formula? (C = 12.0, H = 1.0)
A
\(C_{2}H_{4}\)
B
\(C_{3}H_{4}\)
C
\(C_{3}H_{6}\)
D
\(C_{4}H_{8}\)
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
Given the molecular formula, \(CH_{2}\).
The empirical formula will be \((CH_{2})n\)= 42
\((12+(2\times1))n =42\)
⇒ \(14n =42\)
n = 3, hence the empirical formula is \(C_{3}H_{6}\)
Source: Myschool Past Questions Archive (Record #48970)
Chemistry
WAEC / WASSCE 2018
Oxidation, Reduction & Redox Reactions
Consider the following reaction equation: \(Br_{2} + 2KI \to 2KBr + I_{2}\). Bromine is acting as
A
an oxidizing agent
B
a reducing agent
C
an acid
D
a base
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option A.
Source: Myschool Past Questions Archive (Record #48973)