Physics M.C.Q [1M]

The Young's experiment is performed with the lights of blue (λ = 4360 Å) and green colour (λ = 5460 Å), If the distance of the 4th fringe from the centre is x, then

(a) x (Blue) = x (Green)

(b) x (Blue) > x (Green)

(c) x (Blue) < x (Green)

(d)

The figure shows a double slit experiment P and Q are the slits. The path lengths PX and QX are nλ and (n+2)λ  respectively, where n is a whole number and λ is the wavelength. Taking the central fringe as zero, what is formed at X

(a) First brigh

(b) First dark

(c) Second bright

(d) Second dark

Two coherent sources have intensity in the ratio of  . Ratio of (intensity) max/(intensity) min is

(a)

(b)

(c)

(d)

The oscillating electric and magnetic vectors of an electromagnetic wave are oriented along

(a) The same direction but differ in phase by 90°

(b) The same direction and are in phase

(c) Mutually perpendicular directions and are in phase

(d) Mutually perpendicular directions and differ in phase by 90°

Specific rotation of sugar solution is 0.01 SI units. 200  of impure sugar solution is taken in a polarimeter tube of length 0.25m and an optical rotation of 0.4rad is observed. The percentage of purity of sugar is the sample is

(a) 80%

(b) 89%

(c) 11%

(d) 20%

In the adjacent diagram, CP represents a wavefront and AO & BP, the corresponding two rays. Find the condition on q  for constructive interference at P between the ray BP and reflected ray OP

(a) cosq  = 3l/2d

(b) cosq = l/4d

(c) secq – cosq = l/d

(d) secq – cosq = 4l/d

A thin slice is cut out of a glass cylinder along a plane parallel to its axis. The slice is placed on a flat glass plate as shown. The observed interference fringes from this combination shall be

(a) Straight

(b) Circular

(c) Equally spaced

(d) Having fringe spacing which increases as we go outwards

A ray of light of intensity I is incident on a parallel glass-slab at a point A as shown in fig. It undergoes partial reflection and refraction. At each reflection 25% of incident energy is reflected. The rays AB and A'B' undergo interference. The ratio   is

(a) 4 : 1

(b) 8 : 1

(c) 7 : 1

(d) 49 : 1

If the distance between a point source and screen is doubled, then intensity of light on the screen will become

(a) Four times

(b) Double

(c) Half

(d) One-fourth

In Young's double slit experiment, white light is used. The separation between the slits is b. The screen is at a distance d (d>> b) from the slits. Some wavelengths are missing exactly in front of one slit. These wavelengths are

(a) λ =

(b) λ =

(c) λ =

(d) a, b

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

(a) 4308 Å, 5091 Å, 6222 Å	(b) 4000 Å, 5091 Å, 5600 Å
(c) 4667 Å, 6222 Å, 7000 Å	(d) 4000 Å, 4667 Å, 5600 Å, 7000Å

The maximum intensity in Young's double slit experiment is I₀. Distance between the slits is d = 5 l, where l is the wavelength of monochromatic light used in the experiment. What will be the intensity of light in front of one of the slits on a screen at a distance  D = 10d

(a)

(b)

(c)

(d)

In a two slit experiment with monochromatic light fringes are obtained on a screen placed at some distance from the sits. If the screen is moved by 5   towards the slits, the change in fringe width is 3 . If separation between the slits is , the wavelength of light used is

(a) 6000 Å

(b) 5000 Å

(c) 3000 Å

(d) 4500 Å

Figure here shows P and Q as two equally intense coherent sources emitting radiations of wavelength 20 m. The separation PQ is 5.0 m and phase of P is ahead of the phase of Q by 90^o. A, B and C are three distant points of observation equidistant from the mid-point of PQ. The intensity of radiations at A, B, C will bear the ratio

(a) 0 : 1 : 4

(b) 4 : 1 : 0

(c) 0 : 1 : 2

(d) 2 : 1 : 0

In an interference arrangement similar to Young's double slit experiment, the slits S₁ and S₂ are illuminated with coherent microwave sources each of frequency 10⁶ Hz. The sources are synchronized to have zero phase difference. The slits are separated by distance d = 150 m. The intensity I (𝜃) is measured as a function of q, where q is defined as shown. If I₀ is maximum intensity, then I(θ)  for 0 ≤ θ ≤ 90° is given by

(a) I(θ) =   for  θ = 0°	(b) I(θ) =   for θ = 30°
(c) I(θ) =    for θ =  90°	(d) a, b

Figure represents a glass plate placed vertically on a horizontal table with a beam of unpolarised light falling on its surface at the polarising angle of 57^o with the normal. The electric vector in the reflected light on screen S will vibrate with respect to the plane of incidence in a

(a) Vertical plane

(b) Horizontal plane

(c) Plane making an angle of 45o with the vertical

(d) Plane making an angle of 57o with the horizontal

A circular disc is placed in front of a narrow source. When the point of observation is at a distance of 1 meter from the disc, then the disc covers first HPZ. The intensity at this point is I₀. The intensity at a point distance 25 cm from the disc will be

(a)

(b)

(c)

(d)

Light is an electromagnetic wave. Its speed in vacuum is given by the expression

(a)

(b)

(c)

(d)

The angle of polarisation for any medium is 60^o, what will be critical angle for this

(a)

(b)

(c)

(d)

A parallel monochromatic beam of light is incident normally on a narrow slit. A diffraction pattern is formed on a screen placed perpendicular to the direction of incident beam. At the first maximum of the diffraction pattern the phase difference between the rays coming from the edges of the slit is 

(a) 0

(b)

(c)

(d) 2

When the angle of incidence on a material is 60°, the reflected light is completely polarized. The velocity of the refracted ray inside the material is (in ms^–1)

(a) 3

(b)

(c)

(d) 0.5

In the spectrum of light of a luminous heavenly body the wavelength of a spectral line is measured to be 4747 Å while actual wavelength of the line is 4700 Å. The relative velocity of the heavenly body with respect to earth will be (velocity of light is 3 )

(a) 3 moving  towards the earth

(b) 3  moving away from the earth

(c) 3  moving towards the earth

(d) 3  moving away from the earth

A spectral line λ = 5000 Å in the light coming from a distant star is observed as a 5200 Å. What will be recession velocity of the star

(a) 1.15

(b) 1.15

(c) 1.15

(d) 1.15 km/sec

A light of wavelength 5890 Å falls normally on a thin air film. The minimum thickness of the film such that the film appears dark in reflected light

(a) 2.945

(b) 3.945

(c) 4.95

(d) 1.945

The wavelength of light visible to eye is of the order of

(a)

(b)  m

(c) 1 m

(d) 6  m

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

(a)

(b)

(c)

(d)

What is the path difference of destructive interference

(a) nl

(b) n(λ  + 1)

(c)

(d)

Wavelength of light of frequency 100Hz

(a) 2

(b) 3

(c) 4

(d) 5

If L is the coherence length and c the velocity of light, the coherent time is

(a) cL

(b)

(c)

(d)

Light  coming from a star is observed to have a wavelength of 3737 Å, while its real wavelength is 3700 Å. The speed of the star relative to the earth is [Speed of light 3 ]

(a) 3

(b) 3

(c) 3.7

(d) 3.7

If  is the intensity of the principal maximum in the single slit diffraction pattern, then what will be its intensity when the slit width is doubled

(a)

(b)

(c) 2

(d) 4

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

(a) 1.5

(b) 2.5

(c) 3.5

(d) None of these

In the figure is shown Young’s double slit experiment. Q is the position of the first bright fringe on the right side of O. P is the 11^th fringe on the other side, as measured from Q. If the wavelength of the light used is 6000 ,  then   will be equal to

(a) 6

(b) 6.6

(c) 3.138

(d) 3.144

In hydrogen spectrum the wavelength of  line is 656 nm whereas in the spectrum of a distant galaxy,  line wavelength is 706 nm. Estimated speed of the galaxy with respect to earth is

(a) 2

(b) 2

(c) 2

(d) 2

A beam with wavelength  falls on a stack of partially reflecting planes with separation d. The angle q that the beam should make with the planes so that the beams reflected from successive planes may interfere constructively is (where n = 1, 2, ……)

(a)

(b)

(c)

(d)

An electromagnetic wave travels along z-axis. Which of the following pairs of space and time varying fields would generate such a wave

(a)

(b)

(c)

(d)

The 21 cm radio wave emitted by hydrogen in interstellar space is due to the interaction called the hyperfine interaction is atomic hydrogen. the energy of the emitted wave is nearly

(a)  Joule

(b) 1 Joule

(c) 7  Joule

(d)  Joule

For skywave propagation of a 10 MHz signal, what should be the minimum electron density in ionosphere

(a) ~ 1.2

(b) ~

(c) ~

(d) ~

Two coherent sources of intensities, I₁ and I₂ produce an interference pattern. The maximum intensity in the interference pattern will be

(a) I1 + I2

(b)

(c) (I1 + I2)2

(d)

A parallel plate capacitor of plate separation 2 mm is connected in an electric circuit having source voltage 400 V. if the plate area is 60 cm², then the value of displacement current for   will be

(a) 1.062 amp

(b) 1.062  amp

(c) 1.062  amp

(d) 1.062  amp

In a wave, the path difference corresponding to a phase difference of f is

(a)

(b)

(c)

(d)

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

(a)

(b)

(c)

(d)

A polaroid is placed at 45^o to an incoming light of intensity . Now the intensity of light passing through polaroid after polarisation would be

(a)

(b)

(c)

(d) Zero

A TV tower has a height of 100 m. The average population density around the tower is 1000 per km². The radius of the earth is 6.4  m. the population covered by the tower is

(a) 2

(b) 3

(c) 4

(d) 6

Ratio of amplitude of interfering waves is 3 : 4. Now ratio of their intensities will be

(a)

(b) 49 : 1

(c)

(d) None of these

A rocket is going away from the earth at a speed 0.2c, where c = speed of light. It emits a signal of frequency 4 . What will be the frequency observed by an observer on the earth

(a) 4

(b) 3.2

(c) 3

(d) 5

Radiations of intensity 0.5  are striking a metal plate. The pressure on the plate is

(a) 0.166	(b) 0.332
(c) 0.111	(d) 0.083

A single slit of width a is illuminated by violet light of wavelength 400 nm and the width of the diffraction pattern is measured as y. When half of the slit width is covered and illuminated by yellow light of wavelength 600 nm, the width of the diffraction pattern is

(a) The pattern vanishes and the width is zero	(b) y / 3
(c) 3y	(d) None of these

In Young’s double slit experiment, a minimum is obtained when the phase difference of super imposing waves is

(a) Zero

(b) (2n – 1)π

(c) nπ

(d)  (n + 1) π

In Young’s double slit experiment, the central bright fringe can be identified

(a) By using white light instead of monochromatic light

(b) As it is narrower than other bright fringes

(c) As it is wider than other bright fringes

(d) As it has a greater intensity than the other bright fringes