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Physics
NECO SSCE 2003
Electricity and Magnetism
Solution
A wire of length 100cm and cross-sectional area 2.0 \times 10-3cm2 has a resistance of 0.10 \omega. Calculate its electrical conductivity.
A
2.0 × 10-6 ω-1cm-1
B
5.0 × 105 ω-1cm-1
C
2.0 × 106 ω-1cm-1
D
5.0 × 10-6 ω-1cm-1
E
5.0 × 107 ω-1cm-1
medium Difficulty
Verified Correct Answer: Option B
Physical Principles & Numerical Solution
Electrical conductivity = the reciprocal of resistivity
but resistivity(ρ) = \(\frac{R\times A}{L}\)
resistivity(ρ) = \(\frac{ 2.0 \times 10^{-3} \times0.1}{100}\) = 0.000002
electrical conductivity(σ) = \(\frac{1}{ρ}\)
σ = \(\frac{1}{0.000002} = 500000\omega^{-1}cm^{-1}\)
Source: Myschool Past Questions Archive (Record #42914)
Physics
NECO SSCE 2003
Electricity and Magnetism
The resistance of a series R-C circuit is 5 ω If the impedance of the circuit is 13 ω calculate the reactance of the capacitor
A
12 Ω
B
14 Ω
C
16 Ω
D
18 Ω
E
65 Ω
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 #42918)
Physics
NECO SSCE 2003
Electricity and Magnetism
A transformer is required to give 120V from a 240V mains supply. If the primary has 5500 turns, how many turns has the secondary?
A
232
B
450
C
550
D
2750
E
11000
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 #42930)
Physics
NECO SSCE 2003
Electricity and Magnetism
Lenz’s law of electromagnetic induction states that
A
a force is exerted on a current carrying conductor in a magnetic field
B
the induced current in a conductor is in such a direction as to oppose the change producing it
C
the magnitude of the induced electromotive force in a circuit is proportional to the rate of change of the number of lines of force linking the circuit
D
the magnitude of the induced electromotive force is proportional to the current producing the magnetic flux
E
whenever there is a change in the magnetic flux linked with the circuit, an electromotive is induced
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 #42942)
Physics
WAEC / WASSCE 2003
Electricity and Magnetism
Solution
(a) Explain the term electrolyte and give two examples.
(b) State the relationship between the mass of a substance liberated during electrolysis and the charge passed.
medium Difficulty
Verified Correct Answer: Option
Physical Principles & Numerical Solution
(a) Electrolyte is a substance in liquid or molten state which conducts electricity and undergoes decomposition e.g. metallic salts, acids and alkalis.
(b) M \(\alpha\) Q
M = kQ. Mass m is proportional to charge Q where K is a constant of proportionality.
Source: Myschool Past Questions Archive (Record #54022)
Physics
UTME / JAMB 2002
Electricity and Magnetism
Diagram
Solution
From the diagram above, determine the value of the resistance X
Attached Figure / Diagram
A
6Ω
B
9Ω
C
12Ω
D
15Ω
medium Difficulty
Verified Correct Answer: Option D
Physical Principles & Numerical Solution
Let the combined parallel resistance of 3 Ω and x = Q Ω
∴ Total resistance in the circuit = 2 + Q + 1.5 = 3.5 + Q Ω
Total current in the circuit = 2A
P.D a cross the circuit 12 volts
∴ From Ohm’s law, V = IR
12 = 2(3.5 + Q)
= 7.0 + 2Q
∴ 2Q = 12 – 7
= 5
∴ Q = 5/2 = 2.5 Ω
Thus from parallel formula: I/Q = 1/3 + 1/x
1/2.5 = 1/3 + 1/x
∴ 1/x = 1/2.5 - 1/3 = 3-2.5/7.5 = 0.5/7.5
X = 7.5/0.5 = 75/5 = 15 Ω
∴ X = 15 Ω
Source: Myschool Past Questions Archive (Record #12008)
Physics
UTME / JAMB 2002
Electricity and Magnetism
Diagram
Solution
The electric field between two - point charges is shown in the diagram above. What types of charges are at X and Y?
Attached Figure / Diagram
A
Both X and Y are negative
B
Both X and Y are positive
C
X is positive and Y is negative
D
X is negative and Y is positive
medium Difficulty
Verified Correct Answer: Option B
Physical Principles & Numerical Solution
In the provided diagram, the arrows on the field lines surrounding both point X and point Y are pointing outward. This indicates that both X and Y are negative charges. turn the positive to positive
Source: Myschool Past Questions Archive (Record #12037)
Physics
UTME / JAMB 2002
Electricity and Magnetism
Solution
an electric cell with nominal voltage E has a resistance of 3\Omega connected across it. If the voltage falls to 0.6E, the internal resistance of the cell is
A
1Ω
B
2Ω
C
3Ω
D
4Ω
medium Difficulty
Verified Correct Answer: Option B
Physical Principles & Numerical Solution
IR = 0.6 X I ( R + r )
I X 3 = 0.6 X I ( 3 + r )
3I / 0.6I = 3 + r
5 = 3 + r
r = 2 ohms
Source: Myschool Past Questions Archive (Record #12041)
Physics
UTME / JAMB 2002
Electricity and Magnetism
Solution
A current of 0.5 A flowing 3h Deposits 2g of metal during electrolysis. The quantity of the same metal that would be deposited by the currents of 1.5A flowing in 1h is
A
2g
B
6g
C
10g
D
18g
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
From Faraday's Law, mass deposited during electrolysis is given by
\(M_1 = I_1t_1Z\)
=> Z = \(\frac{M_1}{(I_1t_1)}\)
⇒ Z =\(\frac{2}{0.5 \times3}\) = 1.333Kg/C
For a current of 1.5A flowing for 1h, the mass M, deposited is given by
\(M_2 = ZI_2T_2\) = 1.333 x 1 x 1.5 = 2.0g
\(M_2\) = 2.0g
note: converting time to seconds here is not necessary.
Source: Myschool Past Questions Archive (Record #12262)
Physics
WAEC / WASSCE 2002
Electricity and Magnetism
Which of the following items can be used to compare the relative magnitudes of electric charges on two bodies?
A
ebonite rod
B
gold leaf electroscope
C
proof plane
D
the electrophorus
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 #34089)
Physics
WAEC / WASSCE 2002
Electricity and Magnetism
Local actions is normally prevented in a simple electric cell by
A
introducing an oxidizing agent in the acid
B
not drawing current continously for long period
C
amalgamating the surface of the zinc plate
D
using a porous pot to isolate the zinc plate from the acid
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 #34103)
Physics
WAEC / WASSCE 2002
Electricity and Magnetism
A transformer has 400 turns and 200 turns in the primary and secondary windings respectively. If the current in the primary and secondary windings are 3A and 5A respectively. calculate the efficiency of the transformer?
A
85.0%
B
83.3%
C
37.5%
D
30.0%
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 #34108)
Physics
NECO SSCE 2002
Electricity and Magnetism
Which device does NOT make use of the magnetic effects of an electric current?
A
hot-wire ammeter
B
moving-coil ammeter
C
moving-coil loudspeaker
D
moving-iron ammeter
E
telephone earpiece
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 #42864)
Physics
NECO SSCE 2002
Electricity and Magnetism
Solution
A negatively charged rod is brought near the cap of an electroscope. The cap is earthed momentarily while the charge is near to it. The rod is then removed. Which statement is correct?
A
The cap will be positively charged and the leaf will be negatively charged
B
The cap will be negatively charged and the leaf will be positively changed
C
The cap and the leaf will be positively charged
D
The cap and the leaf will be negatively charged
E
none
medium Difficulty
Verified Correct Answer: Option D
Physical Principles & Numerical Solution
When a negatively charged rod is brought near an electroscope, it repels electrons, making the cap positively charged and the leaves negatively charged. If the cap is earthed while the rod is near, electrons flow in, neutralizing some positive charge and making the cap negatively charged. After removing the rod and disconnecting the earthing, the cap retains extra electrons and remains negatively charged, while the leaves may also be negatively charged depending on their electron loss. Thus, both the cap and the leaves are negatively charged.
Source: Myschool Past Questions Archive (Record #42879)
Physics
NECO SSCE 2002
Electricity and Magnetism
The use of electrical fuses in domestic wiring is
A
to prevent and electrical shock
B
to supply electricity to all the electrical appliances
C
to allow electricity to flow easily through the mains to all the circuits
D
to cut off the mains supply it too high a current flows
E
to fuse all the circuit into one
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 #42882)