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Physics
WAEC / WASSCE 1993
Electricity and Magnetism
Diagram
Solution
In the diagram above, three identical lamps each of 100 W are connected in parallel across a potential difference of 250 V. Calculate the reading of the ammeter.
Attached Figure / Diagram
A
7.5A
B
2.5A
C
1.2A
D
0.8A
E
O.4A
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
P = VI ; I = P/V = 100/250 = 0.4A each
Total current 3 x 0.4 = 1.2A
Source: Myschool Past Questions Archive (Record #25035)
Physics
WAEC / WASSCE 1993
Electricity and Magnetism
Diagram
Solution
Calculate the current, I in the diagram shown above.
(Neglect the internal resistance of the cell)
Attached Figure / Diagram
A
4.0A
B
2.0A
C
1.0A
D
O.5A
E
0.1A.
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
R = 2 + 2 = 4 Ω; 1/R = ¼ + ¼ = 2/4; R = 2Ω
∴ I = V/R = 2/2 = 1A
Source: Myschool Past Questions Archive (Record #25037)
Physics
WAEC / WASSCE 1993
Electricity and Magnetism
Which of the following is not a conductor of electricity?
A
Human body
B
Glass
C
Silver
D
Earth
E
Copper
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 #25038)
Physics
WAEC / WASSCE 1993
Electricity and Magnetism
When a potential difference, V is applied across the ends of a resistor of resistance, R a Current, l passes through the resistor. The heat generated in the resistor in time, t is given by the expression
A
V2lt
B
I2t/R
C
l2Rt
D
lR2tR
E
V2Rt
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 #25040)
Physics
WAEC / WASSCE 1993
Electricity and Magnetism
Electric motor primarily converts
A
electrical energy into chemical energy
B
electrical energy into heat energy
C
kinetic energy into potential energy
D
electrical energy into mechanical energy
E
mechanical energy into light energy
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 #25041)
Physics
UTME / JAMB 1993
Electricity and Magnetism
Solution
Which of the following correctly explains why soft iron is proffered to steel in electromagnets? i. soft iron is more readily magnetized than steel. ii. soft iron is more readily demagnetized than steel. iii. soft iron retains magnetism more than steel.
A
i only
B
ii and iii only
C
i and ii only
D
i, ii, and iii.
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
Soft iron is more readily magnetized than steel (i): Soft iron can become magnetized more easily and reaches saturation quicker than steel.
Soft iron is more readily demagnetized than steel (ii): Soft iron loses its magnetism more quickly when the magnetic field is removed, which is desirable in applications like electromagnets that need to be turned on and off.
Soft iron retains magnetism more than steel (iii): Soft iron does not retain magnetism as well as steel; that is one of the reasons it is used in electromagnets.
Therefore, i and ii are correct.
Source: Myschool Past Questions Archive (Record #28010)
Physics
UTME / JAMB 1993
Electricity and Magnetism
Solution
The terminal voltage of a battery is 4.0V when supplying a current of 2.0A, and 2.0V when supplying a current of 3.0A. The internal resistance of the battery is
A
0.5 \(\Omega\)
B
1.0\(\Omega\)
C
2.0\(\Omega\)
D
4.0\(\Omega\)
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
E = 4 + 2r and E = 2 + 3r
therefore, r = 2\(\Omega\)
Source: Myschool Past Questions Archive (Record #28013)
Physics
UTME / JAMB 1993
Electricity and Magnetism
Solution
A current of 100mA passes through a conductor for 2 minutes. The quantity of electricity transported is
A
200C
B
50C
C
12C
D
0.002C
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
Q = it
= 100 x 10-3 x 2 x 60
= 12C
Source: Myschool Past Questions Archive (Record #28014)
Physics
UTME / JAMB 1993
Electricity and Magnetism
Solution
A 40-W instrument has a resistance of 90\(\Omega\). On what voltage should it be operated normally?
A
60V
B
150V
C
225V
D
3600V
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
P = \(\frac{V}{R}\)
V = \(\sqrt{PR}\)
V = \(\sqrt{40 \times 90}\)
= 60V
Source: Myschool Past Questions Archive (Record #28016)
Physics
UTME / JAMB 1993
Electricity and Magnetism
Solution
Which of the following devices may be used to step up the voltage in a d.c. circuit?
A
a step-up transformer
B
a d.c. generator
C
a wattmeter
D
an induction coil
medium Difficulty
Verified Correct Answer: Option D
Physical Principles & Numerical Solution
An induction coil is a transformer for producing high-voltage alternating current from a low-voltage direct current, consisting essentially of two concentric coils with a common soft-iron core, a primary coil with relatively few windings of heavy wire, and a secondary coil with many turns of fine wire. Excitation of the primary coil by rapidly interrupted or variable current induces high voltage in the secondary coil.
Source: Myschool Past Questions Archive (Record #28017)
Physics
UTME / JAMB 1993
Electricity and Magnetism
Solution
Determine the inductive reactance when a 30.0mH inductor with a negligible resistance is connected to a 1.3 x 103Hz oscillator.
A
39.0\(\Omega\)
B
122.5\(\Omega\)
C
245.0\(\Omega\)
D
39000.0\(\Omega\)
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
XL = 2\(\pi\)FL
= 2 x 3.142 x 30 x 10-3 x 1.3 x 103
= 245\(\Omega\)
Source: Myschool Past Questions Archive (Record #28019)
Physics
UTME / JAMB 1993
Electricity and Magnetism
Solution
Which of the following statements correctly describe(s) cathode rays? i. they consist of tiny particles carrying negative electric charges. ii. they are deflected in a magnetic field but not in an electric field. iii. they consist of fast moving neutrons and deflected in an electric field.
A
i only
B
ii only
C
i and ii only
D
ii and iii only
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
properties of cathode rays among others are ;
The cathode rays consist of negatively charged particles known as electrons.
The cathode rays are deflected from their path by electric and magnetic fields.
Source: Myschool Past Questions Archive (Record #28022)
Physics
UTME / JAMB 1993
Electricity and Magnetism
Diagram
Solution
The current I in the fig above is
Attached Figure / Diagram
A
4.00A
B
1.30A
C
0.80A
D
0.75A
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
Total resistance in series Ra = 4\(\Omega\) and another 4 \(\Omega\)
Forming two resistors in parallel: \(\frac{R_a \times R_b}{R_a + R_b}\) = \(\frac{4 \times 4}{4 + 4}\) = 2 (\Omega\)
and this is in series with the 1 (\Omega\) resistor = 3(\Omega\)
I = \(\frac{12}{3}\) = 4.0A
Source: Myschool Past Questions Archive (Record #41719)
Physics
WAEC / WASSCE 1992
Electricity and Magnetism
In a domestic circuit, electrical appliances and lamps are arranged in parallel across the mains so as to enable the
A
same current to flow through the electrical appliances and the lamps
B
maximum energy to be consumed at least cost
C
same fuse to be used for the electrical appliances and the lamps
D
voltage across the appliances not to be affected when the lamps are switched on and off
E
heat losses to be minimized
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 #24286)
Physics
WAEC / WASSCE 1992
Electricity and Magnetism
Lenz’s law of electromagnetic induction states that
A
electromotive force is induced in a circuit whenever there is a change in the magnetic flux linked with the circuit
B
the induced current in a conductor is in such a direction as to oppose the change producing it
C
the induced e.m.f. in a circuit is proportional to the rate of change of number of lines of force linking the circuit
D
a force is exerted on a current carrying conductor in a magnetic field
E
the induced e.m.f. is proportional to the current producing the magnetic flux.
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 #24288)