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Physics
WAEC / WASSCE 1990
Electricity and Magnetism
Solution
How long will it take to heat 3 kg of water from 28oC to 88oC in an electric taking a current of 6 A from an e.m.f. source of 220V?
A
96s
B
1.20s
C
570s
D
600s
E
1200s
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
Ivt = mcΔθ
t = mcΔθ/Iv = 3x 4200 x (88 - 28)/6 x 200
Source: Myschool Past Questions Archive (Record #24158)
Physics
WAEC / WASSCE 1990
Electricity and Magnetism
Solution
Which of the following reduce(s) the effect of the back e.m.f. generated in the primary coil of an induction coil? The capacitor in the circuit II. The make and break contact in the circuit III. The ratio of turns in the secondary to that in the primary
A
l only
B
II only
C
I and II only
D
II and III only
E
I, II and III.
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
i) The back e.m.f. generated in the primary coil of an induction coil opposes the flow of current in the coil, causing a decrease in the current. This effect can be reduced by using a capacitor in the circuit, which stores the charge and releases it when the current drops. This maintains the flow of current and reduces the effect of the back e.m.f. ii) The make-and-break contact in the circuit also helps to reduce the effect of the back e.m.f. The contact repeatedly breaks the circuit, causing the current to stop flowing momentarily, which interrupts the magnetic field and reduces the back e.m.f.
Source: Myschool Past Questions Archive (Record #24160)
Physics
WAEC / WASSCE 1990
Electricity and Magnetism
Which of the following particles conduct electricity through salty water?
A
Atom
B
molecules
C
Electrons
D
Neutrons
E
Ions
medium Difficulty
Verified Correct Answer: Option E
Physical Principles & Numerical Solution
No expanded working has been attached for this question yet. The verified answer is Option E.
Source: Myschool Past Questions Archive (Record #24161)
Physics
UTME / JAMB 1990
Electricity and Magnetism
One of the properties of the earth's magnetic field is that the
A
north pole lies in the northern hemisphere
B
geographic and magnetic meridians coincide
C
earth's magnetic flux is entirely horizontal at a place where the magnetic dip is zero
D
earth's magnetic flux is entirely vertical at a place where the magnetic dip is zero
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 #28270)
Physics
UTME / JAMB 1990
Electricity and Magnetism
Solution
Three cells each of e.m.f. 1.5v and an internal resistance of 1.0\(\Omega\) are connected in parallel across a load resistance of 2.67\(\Omega\). Calculate the current in the load?
A
0.26A
B
0.41A
C
0.50A
D
0.79A
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
E = 1.5v
rT = \(\frac{1 \times 1\times 1}{(1\times1)+ (1\times1) +(1\times1)}\)
E.m. f = I(R + r) = 0.33\(\Omega\)
1.5 = I(2.67 + 0.33)
I = 0.5A
Source: Myschool Past Questions Archive (Record #28278)
Physics
UTME / JAMB 1990
Electricity and Magnetism
Solution
Which of the following is most suitable for protecting the circuit of 2000W electric iron connected to a 250V mains?
A
13A
B
8A
C
5A
D
3A
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
P = IV \(\Rightarrow\) I = \(\frac{2000}{250}\)
= 8A
The fuse rating should be higher than the calculated current to avoid nuisance blowing, but still protect the circuit. Therefore, the most suitable fuse rating from the options provided would be: 13A
Source: Myschool Past Questions Archive (Record #28287)
Physics
UTME / JAMB 1990
Electricity and Magnetism
Solution
A lamp is rated 240V, 60W. The resistance of the filament is
A
960\(\Omega\)
B
16\(\Omega\)
C
15\(\Omega\)
D
4\(\Omega\)
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
P = \(\frac{V_2}{R}\) \(\Rightarrow\) R = \(\frac{V_2}{p}\)
= \(\frac{240\times 240}{60}\)
= 960\(\Omega\)
Source: Myschool Past Questions Archive (Record #28295)
Physics
UTME / JAMB 1990
Electricity and Magnetism
A 0 - 10mA galvanometer with a coil resistance of 30\(\Omega\) can be converted to a 0 - 10A ammeter by using
A
0.03\(\Omega\) series resistor
B
0.03\(\Omega\) shunt resistor
C
9.99\(\Omega\) shunt resistor
D
9.99\(\Omega\) series resistor
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 #28297)
Physics
WAEC / WASSCE 1989
Electricity and Magnetism
Which of the following substance is not a good conductor of electricity?
A
Human body
B
Glass
C
Aluminium
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 #23911)
Physics
WAEC / WASSCE 1989
Electricity and Magnetism
Which of the following instruments can be used to compare the relative magnitudes of charges on two given bodies?
A
The electrophorous
B
Ebonite rod
C
Proof plane
D
Gold leaf electroscope
E
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 #23915)
Physics
UTME / JAMB 1989
Electricity and Magnetism
Two insulated charged spheres of different sizes and carrying opposite charges are connected together by a metallic conductor. Current will flow from one sphere to the other until both sphere
A
carry the same magnitude and sign of charge
B
are at the same potential
C
are at the same temperature
D
are of the same size
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 #28353)
Physics
UTME / JAMB 1989
Electricity and Magnetism
Solution
A bar magnet is most effectively demagnetized by
A
placing it in a N - S position and hitting it with a hammer
B
subjecting it to an electric current from a battery
C
bringing its north pole in contact with the north pole of a very strong magnet
D
heating the magnet
medium Difficulty
Verified Correct Answer: Option D
Physical Principles & Numerical Solution
the most effective way of demagnetizing a magnet is Electrical method. option c is not correct since battery instead of a solenoid . option A is another method but the placing of the magnet is wrong it should of have been in the east-west direction not north-south direction. option C is not a method. so that leaves us with OPTION d which is also a method of demagnetizing a method, so when a magnets are strongly heated they lose their magnetism. therefore OPTION D is correct.
Source: Myschool Past Questions Archive (Record #28355)
Physics
UTME / JAMB 1989
Electricity and Magnetism
Solution
The resistance of a 5m uniform wire of cross-sectional area 0.2 x 10-6m2 is 0.425. What is the resistivity of the material of the wire?
A
1.10 x 10-6\(\Omega\)m
B
4.25 x 10-6\(\Omega\)m
C
2.40 x 10-7\(\Omega\)m
D
1.70 x 10-8\(\Omega\)m
medium Difficulty
Verified Correct Answer: Option D
Physical Principles & Numerical Solution
Resistance = \(\frac{\text{ Resistivity x Area}}{Area}\)
= 0.425 x 0.2 x 10-6
= 1.7 x 10-8\(\Omega\)m
Source: Myschool Past Questions Archive (Record #28356)
Physics
UTME / JAMB 1989
Electricity and Magnetism
Solution
Three resistors, with substances 250\(\Omega\), 500\(\Omega\) and 1k\(\Omega\) are connected in series. A 6V battery is connected to either end of the combination. Calculate the pot3ential difference between the end of the 250\(\Omega\) resistor.
A
0.20V
B
0.86V
C
1.71V
D
3.43V
medium Difficulty
Verified Correct Answer: Option B
Physical Principles & Numerical Solution
Using voltage - divider method
v1 = \(\frac{(R_1)}{R_T}\)VT
= \(\frac{250}{1750}\) x \(\frac{6}{1}\)
= 0.86V
Source: Myschool Past Questions Archive (Record #28357)
Physics
UTME / JAMB 1989
Electricity and Magnetism
Solution
An ammeter of resistance 1.0\(\Omega\) has a full-scale deflection of 50mA. Determine the resultant full-scale deflection of the meter when a shunt of 0.0111\(\Omega\) is connected across its terminals.
A
400mA
B
450mA
C
500mA
D
550mA
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
V = 0.1 x 50 x 10-3 = 5 x 10-3volts
RT = \(\frac{0.1 \times 0.0111}{0.1 + 0.0111}\)
= 9.99 x 10-3\(\Omega\)
V = IR \(\Rightarrow\) I
= \(\frac{5 \times 10^{-3}}{9.9 \times 10^{-3}}\)
= 0.5A ; = 500mA
Source: Myschool Past Questions Archive (Record #28359)