The height at which the atmosphere ceases to exist is about 80km. If the atmospheric pressure on the ground level is 760mmHg, the pressure at a height of 20km above the ground level is
คำตอบ
(B)
570mmHg
2
A stone of mass 1kg is dropped from a height of 10m above the ground and falls freely under gravity. Its kinetic energy 5m above the ground is then equal to
คำตอบ
(D)
half its initial potential energy
3
If a spherical metal bob of radius 3cm is fully immersed in a cylinder containing water and the water level rises by 1cm, what is the radius of the cylinder?
คำตอบ
(D)
6cm
4
The resultant of two forces acting on an object is maximum if the angle between them is
คำตอบ
(B)
0°
5
I. The earth is not spherical but elliptical in shape
II. Variation in latitude and longitude
III. Rotation of the earth on its axis
IV. Variation in the density of the earth
On which combination of the above does the weight of an object vary on the earth's surface?
คำตอบ
(C)
I, II and III only
6
The efficiency of a machine is always less than 100% because the
คำตอบ
(D)
velocity ratio is always greater than the mechanical advantage
7
Which of the following consists entirely of vector quantities?
คำตอบ
(A)
Velocity, displacement and reaction
8
Ice cubes are added to a glass of warm water. The glass and water are cooled by
คำตอบ
(C)
conduction and convection
9
A ray of light strikes a plane mirror at an angle of incidence of 35°. If the mirror is rotated through 10°, through what angle is the reflected ray rotated?
คำตอบ
(D)
20°
10
The terrestrial telescope has one extra lens more than the astronomical telescope. The extra lens is for
คำตอบ
(D)
erection of the image
11
The driving mirror of a car has a radius of curvature of 1m. A vehicle behind the car is 4m from the mirror. Find the image distance behind the mirror.
คำตอบ
(B)
4/9
12
The pressure of a given mass of a gas changes from 300Nm\(^{-2}\) to 120Nm\(^{-2}\) while the temperature drops from 127°C to -73°C. The ratio of the final volume to the initial volume is
คำตอบ
(B)
5 : 4
13
The thermometric substance of an absolute thermometer is
คำตอบ
(C)
helium
14
A plane sound wave of frequency 85.5Hz and velocity 342ms-1 is reflected from a vertical wall. At what distance from the wall does the wave have antinode?
คำตอบ
(C)
1m
15
A string is fastened tightly between two walls 24cm apart. The wavelength of the second overtone is
คำตอบ
(B)
16cm
16
A gas with initial volume of 2 X 10\(^{-6}m^3\) is allowed to expand to six times its initial value at constant pressure of 2 x 10\(^5Nm^{-2}\). The work done is?
คำตอบ
(A)
2.0J
17
A cell of internal resistance r supplies current to a 6.0Ω resistor and its efficiency is 75%. Find the value of r.
คำตอบ
(D)
2.0Ω
18
A resistance R is connected across the terminal of an electric cell of internal resistance 2Ω and the voltage was reduced to 3/5 of its nominal value.
The value of R is
คำตอบ
(A)
3 Ω
19
A student is at a height 4m above the ground during a thunderstorm. Given that the potential difference between the thundercloud and the ground is 10\(^7\)V, the electric field created by the storm is
คำตอบ
(B)
\(2.5\times 10^6 NC^{-1}\)
20
A working electric motor takes a current of 1.5 A when the p.d across it is 250V. If its efficiency is 80%, the power output is
คำตอบ
(A)
300.0W
21
The cost of running five 60 W lamps and four 100 W lamps for 20 hours if electrical energy cost #10.00 per kwh is
คำตอบ
(D)
140.00
22
In a Daniel cell, the depolarizer, positive and negative electrodes are respectively
คำตอบ
(A)
copper sulphate, copper and zinc
23
when a piece of rectangular glass block is inserted between two parallel capacitor,at constant plate area and distance of separation, the capacitance of the capacitor will
คำตอบ
(A)
increase
24
The ratio of electrostatic force F\(_E\) to gravitational force F\(_G\) between two protons each of charge e and mass m, at a distance d is
คำตอบ
(D)
\(\frac{e^2}{4πε_oGm^2}\)
25
A cell can supply current of 0.4 A and 0.2 A through a 4.0Ω and 10.0Ω resistors respectively.
This internal resistance of the cell is
คำตอบ
(A)
2.0Ω
26
The particles emitted when \( ^{39}_{19}K \text{ decay to } ^{39}_{19}K \) is
คำตอบ
(A)
gamma
27
I. Low pressure.
II. High pressure.
III. High p.d.
IV. Low p.d.
Which combination of the above is true of the conduction of electricity through gases?
คำตอบ
(B)
I and III only
28
The current through a resistor in an a.c circuit is given as 2 sin wt. Determine the d.c. equivalent of the current
คำตอบ
(B)
\(\sqrt{2}\)A
29
The primary coil of a transformer has N turns and is connected to a 120 V a.c. power line. If the secondary coils has 1 000 turns and a terminal voltage of 1 200 volts, what is the value of N?
คำตอบ
(B)
100
30
Which of the following metals will provide the greatest shield against ionizing radiation
คำตอบ
(D)
Lead
31
The process of energy production in the sun is
คำตอบ
(B)
nuclear fussion
32
At reasonance, the phase angle in an a.c. circuit is
คำตอบ
(C)
0°
33
The force on a current carrying conductor in a magnetic field is greatest when the
คำตอบ
(D)
conductor is at right angle with the field
34
A transistor function mainly as a
คำตอบ
(A)
switch and amplifier
35
Energy losses through eddy currents are reduced by using
คำตอบ
(B)
insulated soft iron wires
36
A capacitor of 20 x 10\(^{-12}\)F and an inductor are joined in series. The value of the inductance that will give the circuit a resonance frequency of 200 kHz is
คำตอบ
(D)
\(\frac{I}{32}\) H
37
The magnetic force on a charged particle moving with velocity v is
คำตอบ
(A)
proportional to both the magnitude of the charge and the velocity v
38
In the diagram above, which of the simple pendula will resonate with P when set into oscillation
คำตอบ
(A)
T
39
The diagram above is a block and tackle pulley system in which an effort of 80N is use to lift a load of 240N. The efficiency of the machine is
คำตอบ
(B)
50%
40
If ray travelling in air is incident on a transparent medium as shown in the diagram, the refractive index of the medium is given as
คำตอบ
(A)
cosα / sinβ
41
In the diagram above , the current I is
คำตอบ
(B)
9/11
42
The diagram above shows two capacitors P and Q of capacitance 2μF and 4μF respectively connected to a d.c source. The ratio of energy stored in P to Q is
คำตอบ
(D)
1:2
43
The diagram above shows the capacitors C1, C2 and C3 2μF, 6μF and 3μF respectively. The potential difference across C1, C2 and C3 respectively are
คำตอบ
(D)
6V, 2V and 4V
44
The diagram above shows a closed side 0.5m in a uniform electric field E in the direction shown by the arrows. What is the flux Φ for the box?
คำตอบ
(D)
0.0 E
45
In the circuit diagram above , the ammeter reads a current of 3A when R is 5Ω and 6A when R is 2Ω. Determine the value of x
