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Physics
UTME / JAMB 2014
Electricity and Magnetism
Solution
When a negatively charged rod is brought near the cap of a charged gold leaf electroscope which has positive charges, the leaf
A
Remains the same
B
Collapses
C
Collapses and diverges again
D
Diverges
medium Difficulty
Verified Correct Answer: Option B
Physical Principles & Numerical Solution
When a negatively charged rod is brought near the cap of a charged gold leaf electroscope which has positive charges, the leaf collapses.
Source: Myschool Past Questions Archive (Record #26981)
Physics
UTME / JAMB 2014
Electricity and Magnetism
Solution
What charge is stored in a 0.1F capacitor when a 10V supply is connected across it?
A
1C
B
5C
C
4C
D
2C
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
Q = CV = 0.1 x 10 = 1C
Source: Myschool Past Questions Archive (Record #26982)
Physics
UTME / JAMB 2014
Electricity and Magnetism
Solution
A circuit has a resistance of 200Ω. The resistance of the circuit can be reduced to 120Ω when
A
A 300Ω resistor is connected to it in parallel
B
An 80Ω resistor is conneceted to it in series
C
A 150Ω resistor is connected to it in parallel
D
A 240Ω resistor is connected to it in series
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
A 300Ω resistor is connected to it in parallel
Let R\(_t\) = total resistance in parallel
\(\frac{1}{R_t}\) = \(\frac{1}{R_1}\) + \(\frac{1}{R_2}\) = \(\frac{1}{200}\) + \(\frac{1}{300}\)
R\(_t\) = \(\frac{200 \times 300}{200 + 300}\) = \(\frac{6000}{500}\) = 120 \(\Omega\)
Source: Myschool Past Questions Archive (Record #26985)
Physics
UTME / JAMB 2014
Electricity and Magnetism
Solution
What is the best method of demagnetizing a steel bar magnet?
A
Hammering
B
Heating it
C
Rough handling it
D
Solenoid method
medium Difficulty
Verified Correct Answer: Option D
Physical Principles & Numerical Solution
Solenoid method: This involves placing the magnet inside a solenoid (an electromagnet) and gradually reducing the current. It provides a controlled environment for effective demagnetization.
Source: Myschool Past Questions Archive (Record #26987)
Physics
UTME / JAMB 2014
Electricity and Magnetism
Solution
Calculate the mass of the copper deposited during electrolysis when a current of 4A passes through a copper salt for 2 hours. [Ece of Copper z=3.3x10-7kgC-1]
A
2.9x105kg
B
9.5x10-7kg
C
9.5x10-3kg
D
2.9x104kg
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
Mass = ZIT kg
Mass = 3.3 x 10-7 x 4 x 2 x 60 x 60 kg
Mass = 9.5 x 10-3kg
Source: Myschool Past Questions Archive (Record #26990)
Physics
WAEC / WASSCE 2014
Electricity and Magnetism
An electric motor converts
A
electrical energy to mechanical energy
B
mechanical energy to electrical energy
C
mechanical energy to chemical energy
D
electrical energy to thermal energy
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 #35774)
Physics
WAEC / WASSCE 2014
Electricity and Magnetism
Diagram
Solution
In the circuit diagram above, E is a battery of negligible internal resistance. If its emf is 9.0V. Calculate the current in the circuit ``
Attached Figure / Diagram
A
1.8A
B
1.0A
C
0.8A
D
0.3A
medium Difficulty
Verified Correct Answer: Option B
Physical Principles & Numerical Solution
\(\frac{1}{r} = \frac{1}{r_1} + \frac{1}{r_2}\)
= \(\frac{1}{5} + \frac{1}{20}\)
= \(\frac{4 + 1}{20} = \frac{5}{20}\)
r = \(\frac{20}{5}\)
= 4\(\Omega\)
R = R1 + R2
= 5 + 4
= 9\(\Omega\)
but V = IR
I = \(\frac{V}{R} = \frac{9}{9}\)
= 1A
Source: Myschool Past Questions Archive (Record #35777)
Physics
WAEC / WASSCE 2014
Electricity and Magnetism
Solution
A wire of length 100 cm has a resistance of 10\(\Omega\). If its cross-sectional area is 0.005cm2, determine its resistivity
A
0.0005\(\Omega\)cm
B
0.0015\(\Omega\)cm
C
0.0016\(\Omega\)cm
D
0.0700\(\Omega\)cm
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
e = \(\frac{RA}{L} = \frac{10 \times 0.005}{100} = 0.0005\)
Source: Myschool Past Questions Archive (Record #35778)
Physics
WAEC / WASSCE 2014
Electricity and Magnetism
Solution
A transformer has 400 turns of wire in the primary coil and 40 turns in the secondary col. If the input voltage is 150 volts. Calculate the magnitude of the output voltage
A
150V
B
55V
C
36V
D
15V
medium Difficulty
Verified Correct Answer: Option D
Physical Principles & Numerical Solution
\(\frac{ES}{EP} = \frac{Ns}{Np} = \frac{Es}{150} = \frac{40}{400}\)
Es = \(\frac{150 \times 40}{400}\)
= 15V
Source: Myschool Past Questions Archive (Record #35779)
Physics
WAEC / WASSCE 2014
Electricity and Magnetism
Solution
An electron moves with a speed of 2.00 x 10\(^7\) ms\(^{-1}\) in an orbit in a uniform magnetic field of 1.20 x 10\(^{-3}\) T. Calculate the radius of the orbit. [Mass of an electron = 9.11 x 10\(^{-3}\) kg; charge on an electron = 1.61 x 10\(^{-19}\)C]
medium Difficulty
Verified Correct Answer: Option
Physical Principles & Numerical Solution
\(\frac{Mv^2}{r}\) = qvB
r = \(\frac{MV^2}{qVB} = \frac{9.11 \times 10^{31} \times (2.00 \times 10^7)^2}{1.61 \times 10^{-19} \times 2.00 \times 10^7 \times 1.2 \times 10^{-3}}\)
= 9.43 x 10\(^{-2}\)
Source: Myschool Past Questions Archive (Record #53064)
Physics
WAEC / WASSCE 2014
Electricity and Magnetism
Diagram
Solution
You are provided with a potentiometer AB, a 102\(\Omega\) standard resistor R, a battery of emf 4.5V, a jockey J, and other necessary materials.
Connect a circuit as shown in the diagram above.
Close key K. Without J making contact with AB, read and record the ammeter reading I. Open the key.
Use the jockey to make contact with AB at the 20cm mark such that AJ = x = 20cm. Close the key, read and record the ammeter reading.
Evaluate x\(^{-1}\).
Repeat the procedure for values of x= 35cm, 45cm, 60cm, and 80cm respectively.
Tabulate your readings.
Plot a graph with x\(^{-1}\) on the vertical axis and \(l_i\) on the horizontal axis, starting both axes from the origin (0, 0).
Determine the slope, s, of the graph.
From your graph, determine the value \(l_o\) of \(I_1\) for which x\(^{-1}\)= 0.
Evaluate \(\frac{I_{o}}{I}\).
State two precautions taken to obtain accurate results.
(b)i. Define the emf of a battery.
ii. A cell X of emf 1.018V is balanced by a length of 50.0cm on a potentiometer wire. Another cell Y is balanced by a length of 75.0cm on the same wire. Calculate the emf of Y.
Attached Figure / Diagram
medium Difficulty
Verified Correct Answer: Option
Physical Principles & Numerical Solution
Electricity
I = 0.36A
\(\frac{x}{cm}\)
\(\frac{I}{A}\)
\(\frac{X^{-1}}{cm^{-1}}\)
20.0
1.14
0.050
35.0
0.90
0.029
45.0
0.84
0.022
60.0
0.78
0.017
80.0
0.66
0.013
Slope (s) = \(\frac{\bigtriangleup {X}^{-1}}{\bigtriangleup {I}}\) = \(\frac{0.08-0.01}{1.68-0.644} = \frac{0.07}{1.036}\)
From the graph,
When X\(^{-1}\) = 0
\(I_0\) of \(I_1\) = 0.448A
x. Evaluate \(\frac{I_{0}}{I}\)
= \(\frac{0.448}{0.36}\) = 1.244
Precaution;
The key was opened when readings were not taken.
I ensured tight connections of the connecting wire
I avoided parallax errors when reading the potentiometer.
(bi) Define emf of a battery: The e.m.f of a cell is the potential difference across its terminals when it is in an open circuit. i.e. not Supplying current to an external circuit.
ii. A cell x emf is 1.018V.
Lengt\(h_1\) on the potentiometer x = 50.0cm
Lengt\(h_2\) on the potentiometer, y,= 75.0cm
A cell Y emf is?
Solution
By formula;
\(\frac{E_{1}}{E_{2}}\) = \(\frac{L_{2}}{L_{1}}\)
\(\frac{1.018}{E_{2}} = \frac{75.0}{50.0}\)
75.\(E_2\) = 1.018 x 50
\(E_2\) = \(\frac{1.018\times 50}{75}\)
\(E_2\) = 0.612V.
see graph above
Source: Myschool Past Questions Archive (Record #59978)
Physics
UTME / JAMB 2013
Electricity and Magnetism
Capacitors are used in the induction coil to
A
control circuits
B
prevent distortion of electric fields
C
prevent electric sparks
D
dissipate energy
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 #27360)
Physics
UTME / JAMB 2013
Electricity and Magnetism
Solution
A cell of emf 1.5V is connected in series with a 1Ω resistor and a current of 0.3A flows through the resistor. Find the internal resistance of the cell
A
4.0Ω
B
3.0Ω
C
1.5Ω
D
1.0Ω
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
r = \(\frac{E}{I} - R\)
r = \(\frac{1.5}{0.3} - 1\)
r = 4\(\Omega\)
Source: Myschool Past Questions Archive (Record #27361)
Physics
UTME / JAMB 2013
Electricity and Magnetism
Which of the following obeys ohms laws?
A
electroytes
B
metals
C
diode
D
glass
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 #27362)
Physics
UTME / JAMB 2013
Electricity and Magnetism
Solution
An electric device is rated 2000W, 250V. Calculate the maximum current it can take
A
9A
B
8A
C
7A
D
6A
medium Difficulty
Verified Correct Answer: Option B
Physical Principles & Numerical Solution
I = \(\frac{P}{v}\)
I = \(\frac{2000}{250}\)
I = 8A
Source: Myschool Past Questions Archive (Record #27364)