Marching soldiers crossing a suspension bridge are usually advised to break their steps to avoid damaging the bridge owing to
คำตอบ
(B)
resonance
2
The sharpness of the boundary of the shadow of an object is determined by the
คำตอบ
(A)
intensity of light striking the object
3
A thin converging lens has a power of 4.0 diopters determined its focal length.
คำตอบ
(D)
0.25m
4
A real image three times the size of an object is formed 24cm from a converging mirror. what is the focal length of the mirror.
คำตอบ
(B)
6cm
5
The pair of physical quantities consisting of vectors only are
คำตอบ
(C)
displacement and torque
6
In an ideal wheel an axle system, R stand for the radius of the wheel and r is the radius of the axle. the mechanical advantage is
คำตอบ
(D)
R/r
7
An object is projected from a height of 80 m above the ground with a velocity of 40ms-1 at an angle of 30° to the horizontal. The time of flight [ g ≈ 10m/s\(^2\)
คำตอบ
(B)
4 s
8
In an a.c circuit that contains only a capacitor, the voltage lags behind the current by
คำตอบ
(B)
90°
9
the time it will take a certain radioactive material with a half-life of 50 days to reduce to 1/32of its original number is
คำตอบ
(A)
250days
10
A proton moving with a speed of 1.0 x 10\(^6\)ms\(^{-1}\) through a magnetic field of 1.0T experiences a magnetic force of magnitude 8.0 x 10\(^{-14}\) N. The angle between the proton's velocity and the field is
[1.6 x 10\(^{-19}\)C]
คำตอบ
(C)
30°
11
When impurities are added to semi-conductors, the conductivity of the semi-conductor
คำตอบ
(B)
increases
12
A silicon material is dopped with an element of a certain group and an n-type semi-conductor is formed. the most likely group of the element is
คำตอบ
(A)
V
13
The charge carriers in gasses are
คำตอบ
(B)
electrons and ions
14
The ray which causes gas molecules to glow is known as
คำตอบ
(A)
cathode ray
15
A transformer is rated 240v. If the primary coil is 4000 turns and the secondary voltage 12v, determine the number of turns in the secondary coil.
คำตอบ
(A)
200
16
The current in a reverse-biased junction is due to?
คำตอบ
(A)
minority carriers
17
which of the following materials is a conductor?
คำตอบ
(C)
Sodium
18
When the temperature difference between the wet and dry bulbs of a hygrometer is high, this indicates that
คำตอบ
(D)
the relative humidity is low
19
A 3m3 volume of liquid W of density 200kgm3 is mixed with another liquid L of volume 7m3 and density 150kgm-3. the density of mixture is?
คำตอบ
(A)
165kgm-3
20
A body of mass 36kg falls through a viscous liquid which offers a drag force of 260N on the body. The upthrust on the body at terminal velocity is?
[g = 10ms\(^2\)]
คำตอบ
(A)
100N
21
The process whereby the molecules of different substances move randomly is called?
คำตอบ
(D)
diffusion
22
I. reproducibility
II. Sensibility
III. High thermal capacity
iv. High accuracy
The quantities of a good thermometer include?
คำตอบ
(A)
I, II and IV only
23
The process whereby a liquid turns spontaneously into vapour is called?
คำตอบ
(D)
evaporation
24
I. Melting
II. Boiling
III. Refraction
IV. Conduction
Which combination of the above is evident of the molecular nature of matter?
คำตอบ
(B)
I ,II and IV only
25
When very hot water is poured into two identical thin and thick glass tumblers in equal volumes, the thick one cracks because?
คำตอบ
(D)
of the uneven expansion of glass
26
Satellite communication network makes use of?
คำตอบ
(C)
radio wave
27
An electric device is rated 2000 W, 250 v. The correct fuse rating of the device is?
คำตอบ
(B)
8 A
28
The north pole of a magnet can never be separated from the south pole because of the property knowledge as?
คำตอบ
(C)
magnetic dipole
29
A car battery rated 45 A H is charged with a charger whose rating is 2.5A.How long will it take to charge the battery full?
คำตอบ
(B)
18 hrs
30
The electric field intensity in a place where a charge of 10-10c experiences a force of 0.4N is?
คำตอบ
(D)
4.0 x 109 NC-1
31
Two charged particles are projected into a region where there is a magnetic field perpendicular to their velocities. if the charges are deflected in opposite directions, which of the following statements is true of the charge?
คำตอบ
(A)
the charge must be of opposite sign
32
The resistance of a piece of wire of length 20m has crossed-sectional area 8 x 10\(^{-6}\)m\(^2\)is?
[Resistivity of the wire = 4 x 10\(^{-7}\) Ω m]
คำตอบ
(D)
1.0 Ω
33
The figure above shows a plot of angles of deviation through a glass prism when light is incident at θ degrees on the prism. The incident angle that produces the minimum deviation is
คำตอบ
(D)
25o
34
The value of F in the figure above when in equilibrium is
คำตอบ
(C)
20N
35
In the figure above, the coefficient of static friction is 0.5. If the tension in the string is T, the acceleration of the system in motion is
คำตอบ
(A)
5 ms-2
36
If the system above is in equilibrium, the tension in the string Q is
คำตอบ
(B)
9N
37
In the figure above, the work done by the force of 100N inclined at an angle of 60o to the object dragged horizontally to a distance of 8m is
คำตอบ
(D)
400J
38
In the circuit diagram of a transistor above, the terminal P, Q and R represent
Two liquids L1 and L2 are contained in a U - tube. The height and the density of L1 are 8 cm and 103 kgm-3 respectively. If the density of L2 is 800 kgm-3, its height measured from the same level is
คำตอบ
(B)
10 cm
41
106J of heat is required to boil off completely 2kg of a certain liquid. Neglecting heat lost to the surroundings, the latent heat of vaporization of the liquid is
คำตอบ
(D)
5.0 x 105J kg-1
42
The figure above shows three capacitors, 2μF, 3μF and 6μF connected in series. If the p.d across the system is 12V, the p.d, across the 6μF capacitor is
คำตอบ
(C)
2V
43
If the distance between two point charges its increased by a factor of four, the magnitude of the electrostatic force between them will be
คำตอบ
(B)
1/16 of its former value
44
The velocity of sound in air will be doubled if it's absolute temperature is
คำตอบ
(A)
Quadrupled
45
A force of 200N acts between two objects at a certain distance apart. The value of the force when the distance is halved is
