1999 - JAMB Physics Past Questions and Answers - page 3
21
A 3000W electric cooker is to be used on a 200V mains circuit. Which of the fuses below can be used safely with the cooker?
A
2A
B
5A
C
10A
D
20A
correct option: c
The maximum current drawn by the cooker is given by;
I = P/V
∴ I = 3000/200
I = 15A
Thus the most suitable fuse to be used is a 10A fuse
Users' Answers & CommentsI = P/V
∴ I = 3000/200
I = 15A
Thus the most suitable fuse to be used is a 10A fuse
22
A galvanometer has a resistance of 5Ω. By using a shunt wire of resistance 0.05Ω, the galvanometer could be converted to an ammeter capable of reading 2Amp. What is the current through the galvanometer?
A
2mA
B
10mA
C
20mA
D
25mA
correct option: c
Shunt resistance is usually given as
R = igrg/(I - ig)
Where R = 0.05Ω
rg = 5Ω
I = 2M
∴ ig = IR/(rg + R)
= (2 x 0.05)/(5 + 0.05)
= 0.10/5.05
= 0.0198A
= 19.8mA
= 20mA
Users' Answers & CommentsR = igrg/(I - ig)
Where R = 0.05Ω
rg = 5Ω
I = 2M
∴ ig = IR/(rg + R)
= (2 x 0.05)/(5 + 0.05)
= 0.10/5.05
= 0.0198A
= 19.8mA
= 20mA
23
In fleming's right-hand rule, the thumb, the forefinger and the middle finger if held mutually at right angles represent respectively, the
A
motion, the field and the induced current
B
induced current, the motion and the field
C
field, the induced current and the motion
D
induced current, the field and the motion
correct option: a
Users' Answers & Comments24
At what frequency would a 10H inductor have a reactance of 2000Ω?
A
π/200Hz
B
π/100Hz
C
100/πHz
D
100πHz
correct option: c
Inductive reactance XL = 2πfL
∴ 2πfL = 2000Ω
then f = 2000Ω/2 x π x 10
f = 100/πHz
Users' Answers & Comments∴ 2πfL = 2000Ω
then f = 2000Ω/2 x π x 10
f = 100/πHz
25
The core of an efficient transformer should consist of laminated pieces of metal in order to
A
increase the heat produced by increasing the eddy current
B
increase the heat produced by reducing the eddy current
C
reduce the heat produced by increasing the eddy current
D
reduce the heat produced by reducing the eddy current
correct option: d
Users' Answers & Comments26
Gamma rays are produced when
A
high velocity electrons are abruptly stopped in metals
B
energy changes occur within the nucleus of atoms
C
energy changes occur within the electronic structure of atoms
D
electrons are deflected in very strong magnetic fields
correct option: b
Gamma rays are electromagnetic radiation of nuclear origin; they are produced from energy changes which occur within the nucleus of atoms
Users' Answers & Comments27
What is the speed of a particle of mass 10-27kg whose wavelength is 10-8m.
[h = 6.63 x 10-34Js]
[h = 6.63 x 10-34Js]
A
6.63ms-1
B
66.30ms-1
C
663.00ms-1
D
6630.00ms-1
correct option: b
Energy of a particle is given by
E = hf = hV/λ (since V = fxλ)
But in terms of mass M, E = ∆MV2
∴ ∆MV2 = hV/λ
∆MV = h/λ
∴ V = h/λ∆M
V = 6.63 x 10-34/(10-27 x 10-8)
V = 6.63 x 10-34/10-35
V = 6.63 x 10-34+35
V = 6.63 x 10
V = 66.3ms-1
Users' Answers & CommentsE = hf = hV/λ (since V = fxλ)
But in terms of mass M, E = ∆MV2
∴ ∆MV2 = hV/λ
∆MV = h/λ
∴ V = h/λ∆M
V = 6.63 x 10-34/(10-27 x 10-8)
V = 6.63 x 10-34/10-35
V = 6.63 x 10-34+35
V = 6.63 x 10
V = 66.3ms-1
28
in a series R-L-C circuit at resonance, the voltages across the resistor and the inductor are 30V and 40V respectively, what is the voltage across the capacitor?
A
30V
B
40V
C
50V
D
70V
correct option: b
At resonance, inductive reactant XL is equal to the capacitive reactance XC
i.e. XL = XC
and XL = VL/IL
and XC = VC/IC
Again since the components are in series, the same current flows in the series arrangment
i.e. IL = IC
at resonance, VL/IL = VC/IC
∴ VL = VC
= 40V
Users' Answers & Commentsi.e. XL = XC
and XL = VL/IL
and XC = VC/IC
Again since the components are in series, the same current flows in the series arrangment
i.e. IL = IC
at resonance, VL/IL = VC/IC
∴ VL = VC
= 40V
29
In the Rutherford scattering experiment, a beam of alpha particles was fired at a thin gold film with some of the particles being considerably deflected. This shows that
A
a gold nucleus contains protons, neutrons and electrons uniformly distributed in a tiny volume
B
the gold nucleus is positively charged and is concentrated in a tiny volume
C
the gold nucleus emitted alpha particles
D
the gold nucleus is concentrated in a tiny volume and contains alpha particles
correct option: b
Users' Answers & Comments30
2311Na + Proton → pqX + alpha particle
What are the values of p and q respectively in the equation above?
What are the values of p and q respectively in the equation above?
A
10 and 20
B
12 and 24
C
20 and 10
D
24 and 12
correct option: c
2311Na + Proton → pqX + alpha particle
Represent;
2311Na + 11P → pqX + 42He
Thus from the above equations, p = 20 and q = 10
Users' Answers & CommentsRepresent;
2311Na + 11P → pqX + 42He
Thus from the above equations, p = 20 and q = 10