To concentrate light on the defective teeth, the dentists use
convex mirrors
concave mirrors
convex lens
concave lens
Correct Answer :
B. concave mirrors
Related Questions
Velocity of sound in high altitudes is low because at such a height
the temperature is low
there is no air
the pressure is low
All the above
Stars twinkle because of
refraction of light from them through air
reflection
absorption
All the above
In the electrical circuit of a house the fuse acts as
a thermopile
a load
a step down device
a safety device
The red colour of the setting sun is due to
the least scattered red colour reaching the eye
the dispersion of sun light occurred in air molecule in atmosphere
the diffraction of sunrays in atmospheric layers
interference of all the rays coming from the sun
Of the following which has got the highest frequency?
ultraviolet rays
gamma rays
radio waves
infrared waves
The attraction between similar molecules is called
inertia
adhesion
cohesion
friction
A solid ball of metal has a spherical cavity inside it. When the ball is heated the volume of the cavity will
increase
decrease
remain unaffected
have its shape changed
A bar magnet tied in the middle with a thread is suspended at the South Pole of the earth. The magnet will be in
a horizontal position
a nearly vertical position with its South Pole downwards
a nearly vertical position with its North Pole downwards
a slanting position
A man stands on the pan of a balance holding a fish in his right hand and bucket of water in his left hand. If he transfers the fish into the bucket, the total weight on the pan
increases
decreases
remains the same
first increases and then decreases
When a body is immersed in a fluid the force of buoyancy of the fluid on the body depends on
the immersed volume of the body
density of the liquid
acceleration due to the gravity at the place
All the above
An electric fan converts
electrical energy into heat energy
electrical energy into mechanical energy
mechanical energy into electrical energy
mechanical energy into heat energy
In an electrical circuit, a fuse is connected
in the live wire
in the neutral wire
in the earth wire
anywhere
Frictional force acts in
the same direction as the motion
the opposite direction of the motion
all the directions
upward direction
When light passes from air to glass, its velocity in glass
increases
decreases
remains unchanged
first decreases then increases
The rate of cooling of a hot body depends on
the nature of the radiating surface
area of the radiating surface
temperature difference between the body and the surroundings
All the above
The solar wind is composed of
outward stream of protons and electrons on the surface of the sun during solar flares and sun-spot activity
plasma
ionized gas
All of these
The filament lamp is an example for
fluorescence
incandescence
both (a) and (b)
None of these
X-rays were discovered by
Wilhelm Roentgen
WO Coolidge
Henry Cavendish
William Watson
A hydrogen bomb is based on
nuclear fusion
nuclear fission
Both (a) and (b) above
Neither (a) nor (b)
A bolometer is used to measure
the quantity of heat energy in a body
thermal radiations quantitatively
high temperature
the intensity of sound
Which of the following pairs is not correct?
Television - Baird
Transistor ~ Shockley
Thermometer - Celsius
Barometer Torricelli
If a body is taken from the earth to the moon
both its mass and weight will be different
its mass will be different but the weight will remain the same
its mass and weight will both remain unchanged
its mass will remain the same but weight will be different
Drinks kept in a vacuum flask remain hot or cold as the case may be for a long time because
both walls are silvered on the vacuum side
there is vacuum between the double walls
the cork is a poor conductor of heat
of all the above
Atoms which have the same atomic number but different mass numbers are called
isobars
isomers
isotones
isotopes
Separating particles from a suspension is effected by
centrifugal force
frictional force
gravitational force
distillation
The period of a geostationary (synchronous) satellite orbiting the earth over the equator la
16 hours
12 hours
20 hours
24 hours
Sound waves in air are
transverse
longitudinal
transverse and longitudinal
neither transverse nor longitudinal
Railway tracks are banked on curves so that
the necessary centrifugal force may be obtained from the horizontal component of the weight of the train
the frictional force between the track and the wheels is avoided
the necessary centripetal force may be derived from the horizontal component of the weight of the train
None of these
A rheostat is used
to increase the current flow in a circuit
to decrease the current flow
to measure the flow of electric current
Either (a) or (b) above
The leader of the team who succeeded in constructing the first nuclear reactor (an atomic pile) in the world was
Albert Einstein
Enrico Fermi
HJ Bhabha
Sir Isaac Newton