Dioptre is the unit of power of
convex mirrors
concave mirrors
concave lenses
lenses irrespective of types
Correct Answer :
D. lenses irrespective of types
Related Questions
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 electric fan converts
electrical energy into heat energy
electrical energy into mechanical energy
mechanical energy into electrical energy
mechanical energy into heat energy
The star nearest to the sun is
Proxima Centauri
Sirius
Aldebaran
Vega
Pieces of camphor placed on water move about rapidly. This is because of
diffusion
viscosity
surface tension
capillarity
The SI unit of electric current is
the ampere
the volt
the ohm
the coulomb
Powder clings to the skin because of
cohesion
adhesion
capillary action
absorption
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 spherical mirror is
a reflecting elliptical portion
a reflecting spherical surface
a parabolic reflecting surface
a flat reflecting surface
The stars that shine brightly then dimly and then brightly are known as
meteors
binaries
variable stars
bright stars
The overhead wires supported by high towers in the grid system carry
alternating current of very high frequency
alternating current of very high voltage
a very large direct current
a high voltage direct current
The planet that moves fastest around the sun is
Mars
Venus
Earth
Mercury
The inside of both the walls of a thermos flask is silvered i.e., on the vacuum side in order to reduce heat loss by
convection
radiation
conduction
All the three
Which of the following revolves round the nucleus in an atom?
protons
electrons
neutrons
positrons
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
Warm air will hold more water vapour than cold air because
it is lighter
it has more water vapour in it
its molecules are close together
its molecules are far apart
Compared to the atomic bomb, the destructive power of a hydrogen bomb is
greater
less
equal
can't be determined
In compact porous soil, the rising of the water is due to
capillarity
cohesion
adhesion
viscosity
Rays from the headlight of a motor car are rendered parallel by suitably using
a convex mirror behind it
a concave lens behind it
a concave mirror in front of it
a concave mirror behind it
Rays similar to X-rays but of smaller wave length that are given off by radioactive substances are
a -rays
� -rays
? -rays
Cosmic rays
When white light passes through a glass prism we get a spectrum on the other side of the prism. In the emergent beam the ray which is deviated least is
the violet ray
the red ray
the green ray
the blue ray
When the disturbed electrons of an exited atom transfer back into lower energy levels they emit energy in the form of electromagnetic wave pulses called
neutrons
electrons
phonons
photons
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
The unit of power in SI is
Joule
Newton
Joule/Sec
Erg/Sec
The weight of a body is
maximum at the equator
minimum at the equator
minimum at the poles
the same everywhere
It is easier to climb down a staircase than climb up because in climbing down
work is done against gravity
the steepness of the staircase isn't felt
gravity assists
there is no friction between the legs and steps
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
The shadow below a tree has bright spots in it because
light comes through circular gaps between the leaves
the leaves are circular
the rays bend to form circular spots
the gaps between the leaves act as pin holes
The speed of sound in a medium depends upon the properties of the medium such as
its density
its temperature
its elasticity
All the above
Primary colours are
colours of the rainbow
colours in the spectrum of white light
colours which cannot be produced by mixing other colours
colours found in nature
When ice melts, Its volume
decreases
increases
remains the same until all the ice has melted and then increases
remains the same