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Physics
WAEC / WASSCE 2019
Electricity and Magnetism
Which of the following statements is the correct reason for using soft iron in making the armature or an electric bell?
A
It is a diamagnetic material
B
It loses its magnetism readily
C
It is not easily magnetized
D
It retains its magnetism for a long time
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 #58919)
Physics
WAEC / WASSCE 2019
Electricity and Magnetism
Which of the following devices is used for storing electric charges?
A
Transformer
B
Ammeter
C
Potentiometer
D
Capacitor
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 #58948)
Physics
WAEC / WASSCE 2019
Electricity and Magnetism
Which of the following materials does not serve as a safety device in electrical circuits?
A
Connecting wires
B
Earth wire
C
Fuse
D
Switch
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 #59025)
Physics
WAEC / WASSCE 2019
Electricity and Magnetism
Solution
You are provided with a battery of e.m.f. E, a key K, a voltmeter, a standard resistor \(R_0\) = 2\(\Omega\), a resistance box R, and some connecting wires.
i. Measure and record the e.m.f. E of the battery.
i. Set up a circuit as shown in the diagram above with the key open.
iii. Set the resistance on the resistance box to R 22.
iv. Close the key, read and record the potential difference V on the voltmeter.
v. Evaluate V\(^{-1}\)
vi. Repeat the procedures for five other values of R = 5\(\Omega\) 10\(\Omega\),12\(\Omega\),15\(\Omega\) and 20\(\Omega\). In each case, record V and evaluate V\(^{-1}\)
vii. Tabulate the results.
viii. Plot a graph with R on the vertical axis and V\(^{-1}\) l on the horizontal axis, starting both axes from the origin (0,0).
ix. Determine the slope, s, of the graph and the intercept c on the vertical axis.
x. Calculate \(\propto\) and \(\beta\) from the equations s = \(R_0\) \(\propto\) and c= - (\(R_0\)+B).
xi. State two precautions taken to obtain accurate results.
medium Difficulty
Verified Correct Answer: Option
Physical Principles & Numerical Solution
\(R_0\) = 2\(\Omega\), emf of the battery = 2.0V
Table of value
S/N
R\(\Omega\)
V
V
1
2
3
4
5
6
2
5
10
12
15
20
4.70
2.40
1.75
1.40
1.10
0.76
0.214
0.417
0.571
0.714
0.909
1.320
Slope = \(\frac{\bigtriangleup R}{\bigtriangleup V^{-1}}\) = \(\frac{30.00-0.00}{1.50-0.15}\)
= \(\frac{30.00}{1.35}\) = 22
Intercept on the horizontal axis = 0.15
Calculation of \(\propto\)
\(\propto\) = \(\frac{S}{R_0} = \frac{22}{2}\) = 11
Calculation of \(\beta\)
\(\beta\) = -(\(R_0\) + C) = - (2 + 0.15) = -(2.15) = -2.15
Precuations
- Key opened in between reading/key opened when readings were not taken.
- Tight connections ensured
- Avoided parallax error when taking reading on voltmetre
- Repeated readings shown on table
- Noted/corrected zero error on voltmetre
- Clean terminals ensured.
(b) i. R\(_{AB}\) = \(\frac{4 \times 5}{4+5} = \frac{20}{9}\)
P\(_{AB}\) =\(\frac{V_{AB^2}}{R_{AB}}\)
= \(\frac{4^2 \times9}{20}\) = 7.2 W
ii. I = \(\frac{p}{v}\)=\(\frac{3.6\times10^3}{240}\)
= 15A
The breaker will not open since the current drawn (15A) is less than (20A).
Source: Myschool Past Questions Archive (Record #59786)
Physics
UTME / JAMB 2018
Electricity and Magnetism
Which of the following is true of an electrical charge?
A
Positive charge means deficit electrons
B
Negative charge means excess of electrons
C
electric current means movement of electrons
D
All of the above
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 #47380)
Physics
UTME / JAMB 2018
Electricity and Magnetism
Diagram
Solution
What is the resultant resistance of the circuit in the image shown?
Attached Figure / Diagram
A
8Ω
B
11Ω
C
4Ω
D
3.6Ω
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
First, the two 2-ohm resistors are in parallel
R\(_T\) = \(\frac{2 \times 2}{2 + 2}\) = 1 ohm
Now, the 3, 4, and 1 ohm resistors are in series
Therefore, R\(_eq\) = 3 + 4 + 1 = 8 ohms.
Source: Myschool Past Questions Archive (Record #47382)
Physics
UTME / JAMB 2018
Electricity and Magnetism
Which of the following has the lowest internal resistance when new?
A
Leclanche cell
B
Daniell cell
C
Torch battery
D
Accumulator
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 #47396)
Physics
UTME / JAMB 2018
Electricity and Magnetism
Which of the following obeys Ohm's law?
A
all metals
B
diode only
C
all electrolytes
D
glass
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 #47391)
Physics
UTME / JAMB 2018
Electricity and Magnetism
Solution
A positively charged rod X is brought near an uncharged metal sphere Y and is then touched by a finger with X still in place. When the finger is removed, the result is that Y has
A
no charge and a zero potential
B
a positive charge and a zero potential
C
a negative charge and a positive potential
D
a negative charge and a negative potential
medium Difficulty
Verified Correct Answer: Option D
Physical Principles & Numerical Solution
When a positively charged rod X is brought near an uncharged metal sphere Y, it induces a separation of charges. The side of the sphere near the rod becomes negatively charged as electrons are attracted to it, while the far side becomes positively charged.
When the finger touches the sphere, electrons can flow from the finger into the sphere, giving it an excess of electrons. After removing the finger and the rod, the sphere retains a negative charge.
Source: Myschool Past Questions Archive (Record #47405)
Physics
UTME / JAMB 2018
Electricity and Magnetism
Solution
Electrical appliances in homes are normally earthed so that
A
a person touching the appliances is safe from electric shock
B
both the a.c. and d.c. sources can be used
C
the appliances are maintained at a higher pd than the earth
D
the appliances are maintained at a lower pd than the earth
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
Earthing keeps the metal body of an appliance at earth potential (0 V). If a live wire touches the casing, current flows to the ground, preventing electric shock.
Source: Myschool Past Questions Archive (Record #47406)
Physics
UTME / JAMB 2018
Electricity and Magnetism
Solution
When an atom loses or gain a charge it becomes
A
An electron
B
An ion
C
A neutron
D
A proton
medium Difficulty
Verified Correct Answer: Option B
Physical Principles & Numerical Solution
If an atom gains or loses an electron, it becomes an ion. An atom that gains a negative electron, it becomes a negative ion. If it loses an electron it becomes a positive ion
Source: Myschool Past Questions Archive (Record #47680)
Physics
UTME / JAMB 2018
Electricity and Magnetism
In homes, electrical appliances and lamps are connected in parallel because
A
less current will be used
B
less voltage will be used
C
parallel connection does not heat up the wires
D
series connection uses high voltage
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 #47432)
Physics
UTME / JAMB 2018
Electricity and Magnetism
Solution
Which of the following is an essential physical property of the wires uses for making fuses ?
A
Low density
B
Hypothermal conductivity
C
Low electrical resistivity
D
Low melting point
medium Difficulty
Verified Correct Answer: Option D
Physical Principles & Numerical Solution
Fuse wires have a low melting point so that if a huge amount of current is passed through it to any appliance than that wire would melt and stop the appliance from getting damaged by not letting the current pass any further.
Source: Myschool Past Questions Archive (Record #47725)
Physics
UTME / JAMB 2018
Electricity and Magnetism
Solution
A 40W instrument has a resistance 90 Ohms. On what voltage should it be operated normally
A
60V
B
150V
C
225V
D
360V
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
P = 40W
R = 90W
V = ?
P = \(\frac{V^2}{R}\)
V\(^2\) = PR = 40 x 90
V\(^2\) = 3000
V = \sqrt3600
V = 60N
Source: Myschool Past Questions Archive (Record #47726)
Physics
UTME / JAMB 2018
Electricity and Magnetism
Solution
What flows to the positively charged conductor by connecting it to the earth?
A
Electrons
B
Ion
C
Neutron
D
Proton
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
Earth acts as a ground of zero potential. So when a positively charged conductor is connected to the earth, positive charge flows into the earth and as a result, electrons flow from earth to the conductor.
Source: Myschool Past Questions Archive (Record #47718)