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Physics
WAEC / WASSCE 2012
Current Electricity & Electric Circuits
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.
medium Difficulty
Verified Correct Answer: Option
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: Myschool Past Questions Archive (Record #60004)
Chemistry
UTME / JAMB 2012
Nature of Matter & Separation Techniques
Solution
Which of the following methods can be used to obtain pure water from a mixture of sand, water and methanoic acid?
A
netralization with NaOHfoolowed by filtration
B
neutralization with NaOH followed by distillation
C
fractional distillation
D
filtration followed by distillation
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
To obtain pure water from a mixture of sand, water, and methanoic acid, we need to consider the properties of each component:
- Sand is insoluble in water and can be removed by filtration.
- Methanoic acid (formic acid) is a volatile liquid that can be separated from water by distillation.
- Water is the desired product.
Considering these properties, the correct answer is: Option D. (Filtration followed by distillation)
Here's the step-by-step process:
1. Filtration: Remove the sand from the mixture by passing it through a filter paper.
2. Distillation: Distill the resulting liquid mixture to separate the methanoic acid from the water. Since water has a lower boiling point than methanoic acid, it will vapourize and condense first, allowing you to collect the pure water.
Source: Myschool Past Questions Archive (Record #27464)
Chemistry
UTME / JAMB 2012
Stoichiometry, Mole Concept & Volumetric Analysis
How many atoms are present in 6.0g of magnesium?
[Mg = 24, NA = 6.02 x 1023 mol-1]
A
1.20 x 1022
B
2.41 x 1022
C
1.51 x 1023
D
3.02 x 1023
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option C.
Source: Myschool Past Questions Archive (Record #27465)
Chemistry
UTME / JAMB 2012
Reaction Rates & Chemical Equilibrium
An increase in the pressure exerted on gas at a constant temperature results in
A
a decrease in the number of effective collisions
B
a decrease in volume
C
an increase in the average intermolecular distance
D
an increase in volume
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option B.
Source: Myschool Past Questions Archive (Record #27467)
Chemistry
UTME / JAMB 2012
Stoichiometry, Mole Concept & Volumetric Analysis
2H2(g) + O2(g) → 2H2 O(g)
In the reaction above, what volume of hydrogen would be left over when 300 cm3 of oxygen and 1000 cm3 of hydrogen are exploded in a sealed tube?
A
200 cm3
B
400 cm3
C
600 cm3
D
700 cm3
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option B.
Source: Myschool Past Questions Archive (Record #27468)
Chemistry
UTME / JAMB 2012
Nature of Matter & Separation Techniques
l . Evaporation. ll. Sublimation. lll. Diffusion. IV. Brownian motion.
Which of the above can correctly be listed as evidences for the particulate nature of matter?
A
I and lll only
B
ll and lV only
C
l, ll and lll only
D
l, ll, lll and lV
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 #27469)
Chemistry
UTME / JAMB 2012
Chemical Bonding & Intermolecular Forces
If the elements X and Y have atomic numbers 11 and 17 respectively, what type of bond can they form?
A
Dative
B
Covalent
C
Ionic
D
Metallic
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option C.
Source: Myschool Past Questions Archive (Record #27470)
Chemistry
UTME / JAMB 2012
Atomic Structure, Orbitals & Nuclear Chemistry
A hydrogen atom which has lost an electron contains
A
one proton only
B
one neutron only
C
one proton and one neutron
D
one proton, one electron and one neutron
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 #27471)
Chemistry
UTME / JAMB 2012
Atomic Structure, Orbitals & Nuclear Chemistry
The electronic configuration of Mg 2+ is
A
ls 22s 22P 63s23P2
B
Is22s22P6
C
ls22s22p63s2
D
ls22s22P4
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option B.
Source: Myschool Past Questions Archive (Record #27472)
Chemistry
UTME / JAMB 2012
Periodic Table & Periodicity
Group VII elements are
A
monoatmic
B
good oxidizing agents
C
highly electropositive
D
electron donors
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option B.
Source: Myschool Past Questions Archive (Record #27473)
Chemistry
UTME / JAMB 2012
Stoichiometry, Mole Concept & Volumetric Analysis
Which of the following is used to study the arrangement of particles in crystal lattices?
A
Alpha-particles
B
Beta-particles
C
Gamma-rays
D
X-rays
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 #27474)
Chemistry
UTME / JAMB 2012
Periodic Table & Periodicity
I. It has a varied composition from one place to another. ll. it constituents can be separated by physical means
lll. It contains unreactive noble gases
which of the above shows that air is a mixture?
A
I and ll only
B
ll and lll only
C
l and lll only
D
l,ll and lll
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 #27475)
Chemistry
UTME / JAMB 2012
Water, Solutions & Solubility
The chemicals used to soften hard water involves the addition of
A
insoluble sodium compounds which from soluble solutions of calcium and magesium
B
solube soudium compounds which from soluble solutions of calcium and magnesium ions
C
solube sodium compounds which from insoluble precipitates of calcium and magnesium ions
D
insoluble precipitates of calcium and magnesium ions
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option C.
Source: Myschool Past Questions Archive (Record #27476)
Chemistry
UTME / JAMB 2012
Water, Solutions & Solubility
Chlorination of water for town supply is carried out to
A
make the water colourless
B
remove germs from the water
C
make the water tastedful
D
remove odour from the water
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option B.
Source: Myschool Past Questions Archive (Record #27477)
Chemistry
UTME / JAMB 2012
Water, Solutions & Solubility
The solubilites of different solutes in a given solvent can be compared by
A
plotting their solubility curves on separete axes
B
plotting their solubility curves on the same axes
C
plotting some of the solubility curves on the x-axis and others on the y-axis
D
plotting their solubility curves on the x-axis only
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option B.
Source: Myschool Past Questions Archive (Record #27478)