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Light Waves Physics - Light Waves

Rajasthan Board (RBSE) - STD 12 Science - Physics (Rajasthan - English Medium). 79 questions in this chapter.

Question types

Light Waves question types

79 questions across 6 question groups — pick any mix to generate a Physics paper with step-by-step answer keys.

79
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6
Question groups
5
Question types
Sample Questions

Light Waves questions

One sample from each question group in this chapter. Select any group above to see the full set with answer keys.

Q 1M.C.Q (1 Marks)1 Mark
The inverse square law of intensity $\Big(\text{i.e., the intensity}\propto\frac{1}{\text{r}^2}\Big)$ is valid for a:
  1. Point source.
  2. Line source.
  3. Plane source.
  4. Cylindrical source.
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Q 2M.C.Q (1 Marks)1 Mark
The slits in a Young's double slit experiment have equal width and the source is placed symmetrically with respect to the slits. The intensity at the central fringe is $I_0$. If one of the slits is closed, the intensity at this point will be:
  • ✓
    $\text{I}_0$
  • B
    $\frac{\text{I}_0}{4}$
  • C
    $\frac{\text{I}_0}{2}$
  • D
    $4\text{I}_0$

Answer: A.

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Q 3M.C.Q (1 Marks)1 Mark
Suppose the medium in the previous question is water. Select the correct option$(s)$ from the list given in that question.
  • A
    $v_A > v_B > v_C$
  • B
    $v_A < v_B < v_C$
  • ✓
    $v_A = v_B = v_C$
  • D
    $\text{v}_\text{B}=\frac{1}{2}(\text{v}_\text{A}+\text{v}_\text{C})$

Answer: C.

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Q 4M.C.Q (1 Marks)1 Mark
The wavefronts of a light wave travelling in vacuum are given by $x + y + z = c.$ The angle made by the direction of propagation of light with the $X-$axis is:
  • A
    $0^\circ$
  • B
    $45^\circ$
  • C
    $90^\circ$
  • ✓
    $\cos^{-1}\Big(\frac{1}{\sqrt{3}}\Big)$

Answer: D.

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Q 5M.C.Q (1 Marks)1 Mark
Three observers $A, B$ and $C$ measure the speed of light coming from a source to be $vA, 0B$ and $vc.$ The observer $A$ moves towards the source and $C$ moves away from the source at the same speed. The observer $B$ stays stationary. The surrounding space is vacuum everywhere.
  • A
    $\text{v}_\text{A} > \text{v}_\text{B} > \text{v}_\text{C}.$
  • B
    $\text{v}_\text{A} < \text{v}_\text{B} < \text{v}_\text{C}$
  • ✓
    $\text{v}_\text{A}=\text{v}_\text{B}=\text{v}_\text{C}$
  • D
    $\text{v}_\text{B}=\frac{1}{2}(\text{v}_\text{A}+\text{v}_\text{C})$

Answer: C.

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Q 61 Marks Question1 Mark
Find the thickness of a plate which will produce a change in optical path equal to half the wavelength $\lambda$ of the light passing through it normally. The refractive index of the plate is $\mu$.
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Q 71 Marks Question1 Mark
Consider the situation of the previous problem. If the mirror reflects only 64% of the light energy falling on it, what will be the ratio of the maximum to the minimum intensity in the interference pattern observed on the screen?
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Q 81 Marks Question1 Mark
Plane microwaves are incident on a long slit having a width of 5.0cm. Calculate the wavelength of the microwaves if the first diffraction minimum is formed at $\theta=30^\circ.$
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Q 92 Marks Questions2 Marks
White light is used in a Young's double slit experiment. Find the minimum order of the violet fringe $(\lambda=400\ \text{nm}),$ which overlaps with a red fringe $(\lambda=700\ \text{nm}).$
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Q 102 Marks Questions2 Marks
The linewidth of a bright fringe is sometimes defined as the separation between the points on the two sides of the central line where the intensity falls to half the maximum. Find the linewidth of a bright fringe in a Young's double slit experiment in terms of $\lambda$, d and D where the symbols have their usual meanings.
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Q 112 Marks Questions2 Marks
In a Young's double slit experiment $\lambda=500\ \text{nm}, d = 1.0\ mm$ and $D = 1.0m$. Find the minimum distance from the central maximum for which the intensity is half of the maximum intensity.
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Q 122 Marks Questions2 Marks
A double slit $S_1 - S_2$ is illuminated by a coherent light of wavelength $\lambda$. The slits are separated by a distance $d$. A plane mirror is placed in front of the double slit at a distance $D_1$ from it and a screen $\sum$ is placed behind the double slit at a distance $D_2$ from it $($figure $17-E_2)$. The screen $E$ receives only the light reflected by the mirror. Find the fringe$-$width of the interference pattern on the screen.
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Q 132 Marks Questions2 Marks
Two transparent slabs having equal thickness but different refractive indices $\mu_1$ and $\mu_2$ are pasted side by side to form a composite slab. This slab is placed just after the double slit in a Young's experiment so that the light from one slit goes through one material and the light from the other slit goes through the other material. What should be the minimum thickness of the slab so that there is a minimum at the point $P_0$ which is equidistant from the slits?
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Q 143 Marks Question3 Marks
Suppose white light falls on a double slit but one slit is covered by a violet filter (allowing $\lambda=400\text{nm}$). Describe the nature of the fringe pattern observed.
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Q 153 Marks Question3 Marks
Can we perform Young's double slit experiment with sound waves? To get a reasonable "fringe pattern", what should be the order of separation between the slits? How can the bright fringes and the dark fringes be detected in this case?
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Q 173 Marks Question3 Marks
Is the colour of 620nm light and 780nm light same? Is the colour of 620nm light and 621nm light same? How many colours are there in white light?
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Q 183 Marks Question3 Marks
A narrow slit S transmitting light of wavelength $\lambda$ is placed a distance d above a large plane mirror as shown in figure (17-E1). The light coming directly from the slit and that coming after the reflection interfere at a screen $\sum$ placed at a distance D from the slit.
  1. What will be the intensity at a point just above the mirror, i.e., just above O?
  2. At what distance from 0 does the first maximum occur?
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Q 194 Marks Questions4 Marks
TV signals broadcast by Delhi studio cannot be directly received at Patna which is about 1000km away. But the same signal goes some 36000km away to a satellite, gets reflected and is then received at Patna. Explain.
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Q 204 Marks Questions4 Marks
Why don't we have interference when two candles are placed close to each other and the intensity is seen at a distant screen? What happens if the candles are replaced by laser sources?
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Q 215 Marks Questions5 Marks
A glass surface is coated by an oil film of uniform thickness $1.00 \times 10^{-4}\ cm.$ The index of refraction of the oil is $1.25$ and that of the glass is $1.50.$ Find the wavelengths of light in the visible region $(400\ nm - 750\ nm)$ which are completely transmitted by the oil film under normal incidence.
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Q 225 Marks Questions5 Marks
A thin paper of thickness $0.02\ mm$ having a refractive index $1.45$ is pasted across one of the slits in a Young's double slit experiment. The paper transmits $\frac{4}{9}$ of the light energy falling on it.
  1. Find the ratio of the maximum intensity to the minimum intensity in the fringe pattern.
  2. How many fringes will cross through the centre if an identical paper piece is pasted on the other slit also? The wavelength of the light used is 600nm.
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Q 235 Marks Questions5 Marks
Figure shows three equidistant slits being illuminated by a monochromatic parallel beam of light.
Let $\text{BP}_0-\text{AP}=\frac{\lambda}{3}$ and $\text{D}>\lambda.$
  1. Show that in this case $\text{d}=\sqrt{\frac{2\lambda\text{D}}{3}}.$
  2. Show that the intensity at $P,$ is three times the intensity due to any of the three slits individually.
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Q 245 Marks Questions5 Marks
Two coherent point sources $S_1$ and $S_2$ vibrating in phase emit light of wavelength $\lambda$. The separation between the sources is $2\lambda$. Consider a line passing through $S_2$ and perpendicular to the line $S_1S_2.$ What is the smallest distance from $S_2$ where a minimum of intensity occurs?
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Q 255 Marks Questions5 Marks
Consider the situation shown in figure $(17-E6).$ The two slits $S_1$ and $S_2$ p laced symmetrically around the central line are illuminated by a monochromatic light of wavelength $\lambda.$ The separation between the slits is $d.$ The light transmitted by the slits falls on a screen $E_1$ placed at a distance $D$ from the slits. The slit $S_3$ is at the central line and the slit $S_4$ is at a distance $z$ from $S_3.$ Another screen $\sum_2$ is placed a further distance $D$ away from $\sum_1$. Find the ratio of the maximum to minimum intensity observed on $\sum_2$, if z is equal to,
  1. $\text{z}=\frac{\lambda\text{D}}{2\text{d}}$
  2. $\frac{\lambda\text{D}}{\text{d}}$
  3. $\frac{\lambda\text{D}}{4\text{d}}$
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