The cover of a solar cooker is made of glass because
it absorbs sun's rays
it reflects sun's rays
it retains the heat inside by the greenhouse effect
it radiates heat better than metals
Correct Answer :
C. it retains the heat inside by the greenhouse effect
Related Questions
The planet that is known as earth's twin is
Mercury
Venus
Moon
Mars
Cyclotron is an apparatus used
as an accelerator for imparting energies to charged particles of atomic magnitudes
to reduce the charge on a particle
to produce intense magnetic field
to produce intense electrical field
Lightning is produced when
similar charges of electricity rush towards each other and then get repelled
clouds strike against impurities in air and the friction burns up these impurities
strong opposite charges in different clouds break down the resistance offered by the intervening air
water vapour produces electricity in the clouds
A cup of hot coffee is placed on a metal table in a room. By which of the following methods does it lose heat?
conduction and convection only
conduction and radiation only
convection and radiation only
conduction, convection and radiation
The body of an electrical appliance is earthed in order that
electricity may not leak
there may be smooth flow of electricity
a short circuit may be prevented
current may pass to the earth in case of a short circuit without doing any harm to the person
The brightest planet in the Solar System is
Jupiter
Mercury
Venus
Sirius
The minimum velocity required by a satellite to escape earth's gravitational pull is
18 km/s
11.2 km /s
21 km/s
35 km/s
At what temperature do the Fahrenheit and Celsius scales give the same reading?
212°
32°
-40°
0°
In a river, the currents are fastest where the river la
wide and shallow
narrow and shallow
wide and deep
narrow and deep
A body has fallen from a height. Just before touching the pound it has
lost all its potential energy and gained an equivalent amount of kinetic energy
gained potential energy and lost kinetic energy
gained kinetic energy as well as potential energy
lost kinetic energy as well as potential energy
A projectile is fired at an angle with the horizontal with a small velocity. Its horizontal range will be maximum when the angle with the horizontal is
0°
30°
45°
60°
A spherical mirror is
a reflecting elliptical portion
a reflecting spherical surface
a parabolic reflecting surface
a flat reflecting surface
Commonly used safety fuse wire is made of
Tin
Lead
Nickel
An alloy of tin and lead
The mirage is a phenomenon
generally considered as a desert happening
caused by unequal heating of the several layers of the atmosphere above the desert
in which the refracted rays take a curved path resulting in total internal refection
All the above
For accurate scientific work, temperatures are often measured by
mercury thermometers
alcohol thermometers
platinum resistance thermometers
thermoelectric thermometers
The number of electrons in the outer orbits of a nucleus gives
the mass number
atomic number
atomic weight
absolute number
The image formed by a plane mirror is
of the same size as the object
at the same distance behind the mirror as the object is in front of it
virtual and laterally inverted
All the above
A person does not sink in the Dead Sea because
the sea contains a large amount of other salts besides sodium chloride
the density of the person is less than the density of the Dead Sea water
of the surface tension due to salt water in the Dead Sea
of difference in mass
A person cups his hand around the mouth when shouting. Why?
Sound energy from his mouth is then directed in one direction
The cupped hand acts as a cardboard tube of short length
The pitch of sound increases
Both (a) and (b)
A heavenly body similar in nature to the sun intensely hot glowing mass that produces its energy by thermonuclear reactions is
a planet
a meteor
a star
a comet
The instrument used to measure atmospheric pressure is
Pyrometer
Eudiometer
Barometer
Hydrometer
A radio set that uses valves does not start operating immediately when it is switched on whereas a set containing only tranaistors operates immediately. The reason for this is that
the valve filaments have low resistance
valve-radio sets work at a higher voltage
transistor set has a low resistance
filaments of the valves cake time to beat up and function
Which is the densest planet of the solar system?
Sun
Jupiter
Mercury
Earth
The earth's nearest neighbour in space is
the Sun
the Moon
the Venus
the Mars
The resistance of a wire depends on
the material of the wire
the length of the wire
the cross section of the wire
All the above
For accurate scientific work, temperatures are often measured by
mercury thermometers
alcohol thermometers
platinum resistance thermometers
thermoelectric thermometers
Solids have definite shapes. This is because
the forces of cohesion of the molecules within are very much less in them
the forces of cohesion are very large
the forces of adhesion are large
the forces of adhesion are less
An ohm is a unit of
potential difference
resistance
current
All the above
The theory that the earth constituted the centre of the universe around which the sun and the planets revolved was propounded by
Copernicus
Ptolemy
Newton
Kepler
When a body is partly or wholly immersed in a liquid the apparent loss of weight is equal to the weight of the liquid displaced by the submerged portion. This is known as
Pascal's law
Bernoulli's law
Archimedes' law
Boyle's law