CBSE
Multiple Choice QuestionsAssertion: There are very small sporadic changes in the period of rotation of the earth.
Reason: Shi fling of large air masses in the earth's atmosphere produce a change in the moment of inertia of the earth causing its period of rotation to change.
If both assertion and reason are true and reason is the correct explanation of assertion
If both assertion and reason are true but reason is not the correct explanation of assertion
If assertion is true but reason is false
If both assertion and reason are false
The minimum wavelength of X-rays emitted by X-ray tube is 0.4125 Å. The accelerating voltage is :
30 kV
50 kV
80 kV
60 kV
If vg, vx and vm are the speeds of gamma rays, X rays and microwaves respectively in vacuum then :
vg > vm > vx
vg > vx > vm
vg = vm = vx
none of these
X-ray beam are affected by
electric field
magnetic field
both (a) and (b)
none of these
In case of linearly polarised light, the magnitude of the electric field vector
does not change with time
varies periodically with time
increases and decreases linearly with time
is parallel to the direction of propagation
In short wave communication, waves of which of the following frequencies will be reflected back by the ionospheric layer having electron density 1011 per m3 ?
2 MHz
10 MHz
12 MHz
18 MHz
All components of the electromagnetic spectrum in vacuum have the same
energy
velocity
wavelength
frequency
Assertion: The true geographic north direction is found by using a compass needle.
Reason: The impurities meridian of the earth is along the axis of rotation of the earth.
If both assertion and reason are true and reason is the correct explanation of assertion
If both assertion and reason are true but reason is not the correct explanation of assertion
If assertion is true but reason is false
If both assertion and reason are false
The maximum distance upto which TV transmission from a TV of height h can be received is proportional to
h1/2
h
h3
h2
The difference between soft and hard X-rays is of :
velocity
intensity
frequency
polarization
