Physics M.C.Q (1 Marks)

Assertion : Radio waves can be polarised.
Reason : Sound waves in air are longitudinal in nature.

Assertion : Ultraviolet radiation are of higher frequency waves are dangerous to human being.
Reason : Ultraviolet radiation are absorbed by the atmosphere

A laser beam can be focussed on an area equal to the square of its wavelength A He-Ne laser radiates energy at the rate of 1mW and its wavelength is 632.8 nm. The intensity of focussed beam will be

Assertion : For cooking in a microwave oven, food is always kept in metal containers.
Reason : The energy of microwave is easily transferred to the food in metal container.

Assertion : The electrical conductivity of earth’s atmosphere decrease with altitude.
Reason : The high energy particles (i.e. g-rays and cosmic rays) coming from outer space and entering our earth’s atmosphere causes ionisation of the atoms of the gases present there and the pressure of gases decreases with increase in altitude.

Assertion : Television signals are received through sky-wave propagation.
Reason : The ionosphere reflects electromagnetic waves of frequencies greater than a certain critical frequency.

Assertion : The cloud in sky generally appear to be whitish.
Reason : Diffraction due to clouds is efficient in equal measure at all wavelengths.

Assertion : Corpuscular theory fails in explaining the velocities of light in air and water.
Reason : According to corpuscular theory, light should travel faster in denser medium than, in rarer medium.

Assertion : Microwave communication is preferred over optical communication.
Reason : Microwaves provide large number of channels and band width compared to optical signals.

Assertion : Thin films such as soap bubble or a thin layer of oil on water show beautiful colours when illuminated by white light.
Reason : It happens due to the interference of light reflected from the upper surface of the thin film.

Assertion : When a tiny circular obstacle is placed in the path of light from some distance, a bright spot is seen at the centre of shadow of the obstacle.
Reason : Destructive interference occurs at the centre of the shadow.

Assertion : Coloured spectrum is seen when we look through a muslin cloth.
Reason : It is due to the diffraction of white light on passing through fine slits.

Assertion : In Young’s experiment, the fringe width for dark fringes is different from that for white fringes.
Reason : In Young’s double slit experiment the fringes are performed with a source of white light, then only black and bright fringes are observed.

Assertion : In everyday life the Doppler’s effect is observed readily for sound waves than light waves.
Reason : Velocity of light is greater than that of sound.

Assertion : The unpolarised light and polarised light can be distinguished from each other by using polaroid.
Reason : A polaroid is capable of producing plane polarised beams of light.

Assertion : In Young’s double slit experiment, the fringes become indistinct if one of the slits is covered with cellophane paper.
Reason : The cellophane paper decrease the wavelength of light.

Assertion : For best contrast between maxima and minima in the interference pattern of Young’s double slit experiment, the intensity of light emerging out of the two slits should be equal.
Reason : The intensity of interference pattern is proportional to square of amplitude.

Assertion : The film which appears bright in reflected system will appear dark in the transmitted light and vice-versa.
Reason : The conditions for film to appear bright or dark in reflected light are just reverse to those in the transmitted light.

Assertion : Newton’s rings are formed in the reflected system. When the space between the lens and the glass plate is filled with a liquid of refractive index greater than that of glass, the central spot of the pattern is dark.
Reason : The reflection is Newton’s ring cases will be from a denser to a rarer medium and the two interfering rays are reflected under similar conditions.

Assertion : No interference pattern is detected when two coherent sources are infinitely close to each other.
Reason : The fringe width is inversely proportional to the distance between the two slits.

Assertion : A narrow pulse of light is sent through a medium. The pulse will retain its shape as it travels through the medium.
Reason : A narrow pulse is made of harmonic waves with a large range of wavelengths.

A beam of electron is used in an YDSE experiment. The slit width is d. When the velocity of electron is increased, then

The k line of singly ionised calcium has a wavelength of 393.3 nm as measured on earth. In the spectrum of one of the observed galaxies, this spectral line is located at 401.8 nm. The speed with which the galaxy is moving away from us, will be

A beam of natural light falls on a system of 6 polaroids, which are arranged in succession such that each polaroid is turned through 30° with respect to the preceding one. The percentage of incident intensity that passes through the system will be

Assertion : Environmental damage has increased the amount of ozone in the atmosphere.
Reason : Increase of ozone increases the amount of ultraviolet radiation on earth.

In Young's double slit experiment, if monochromatic light is replaced by white light

Assertion : Short wave bands are used for transmission of ratio waves to a large distance
Reason : Short waves are reflected by ionosphere

Assertion : In Hertz experiment, the electric vector of radiation produced by the source gap is parallel to the gap.
Reason : Production of sparks between the detector gap is maximum when it is placed perpendicular to the source gap.

Assertion : Only microwaves are used in radar.
Reason : Because microwaves have very small wavelength.

The ratio of the intensity at the centre of a bright fringe to the intensity at a point one-quarter of the distance between two fringe from the centre is

Among the two interfering monochromatic sources A and B; A is ahead of B in phase by 66°. If the observation be taken from point P, such that PB – PA = l/4. Then the phase difference between the waves from A and B reaching P is

White light may be considered to be a mixture of waves with l ranging between 3900 Å and 7800 Å. An oil film of thickness 10,000 Å is examined normally by reflected light. If m = 1.4, then the film appears bright for

The ratio of intensities of consecutive maxima in the diffraction pattern due to a single slit is

In a single slit diffraction experiment first minimum for red light (660 nm) coincides with first maximum of some other wavelength l'. The value of l' is

Two coherent sources separated by distance d are radiating in phase having wavelength l. A detector moves in a big circle around the two sources in the plane of the two sources. The angular position of n = 4 interference maxima is given as

Two point sources X and Y emit waves of same frequency and speed but Y lags in phase behind X by 2pl radian. If there is a maximum in direction D the distance XO using n as an integer is given by

In a double slit arrangement fringes are produced using light of wavelength 4800 Å. One slit is covered by a thin plate of glass of refractive index 1.4 and the other with another glass plate of same thickness but of refractive index 1.7. By doing so the central bright shifts to original fifth bright fringe from centre. Thickness of glass plate is

In Young’s double slit experiment, the two slits act as coherent sources of equal amplitude A and wavelength l. In another experiment with the same set up the two slits are of equal amplitude A and wavelength l but are incoherent. The ratio of the intensity of light at the mid-point of the screen in the first case to that in the second case is