Gr Xii Physics- Part-2 Revision 2
Mixed Questions from Ray Optics, Wave Optics , Dual Nature
Questions and Answers
- 1.
What is path difference for destructive interference?
- A.
(a) nλ
- B.
(b) n(λ +1)
- C.
(c) (2n + 1)λ/2
- D.
(d) (n +1)λ/ 2
Correct Answer
C. (c) (2n + 1)λ/2Explanation
The path difference for destructive interference is given by the equation (2n + 1)λ/2. This equation represents the phase difference between two waves that results in destructive interference. The term (2n + 1) represents the number of half-wavelengths of the waves, and λ represents the wavelength of the waves. Dividing this by 2 gives the path difference. This equation is derived from the concept that destructive interference occurs when the crests of one wave align with the troughs of the other wave, resulting in cancellation of the waves.Rate this question:
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- 2.
When exposed to sunlight, thin films of oil on water of ten exhibit brilliant colours due to the phenomenon of
- A.
Interference
- B.
Diffraction
- C.
Dispersion
- D.
Refraction
Correct Answer
A. InterferenceExplanation
When thin films of oil on water are exposed to sunlight, they exhibit brilliant colors due to the phenomenon of interference. Interference occurs when light waves interact with each other, either constructively or destructively. In this case, the thin film of oil acts as a medium that reflects and refracts light waves. As the light waves pass through the film and reflect off the water surface, they interfere with each other, resulting in the observed colorful patterns. This phenomenon is responsible for the vibrant colors seen in soap bubbles and oil slicks on water.Rate this question:
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- 3.
What happens, if the monochromatic light used in Young’s double slit experiment is replaced by white light?
- A.
(a) No fringes are observed.
- B.
(b) All bright fringes become while.
- C.
(c) All bright fringes have colour between violet and red.
- D.
(d) Only the central fringe is white and all other fringes are coloured.
Correct Answer
D. (d) Only the central fringe is white and all other fringes are coloured.Explanation
When monochromatic light is used in Young's double slit experiment, interference fringes are observed. However, when white light is used instead, the different wavelengths of light interfere with each other, causing the fringes to become colored. The central fringe appears white because it is formed by the overlapping of all the different colors of light. The other fringes appear colored because different colors of light interfere constructively or destructively at different points, resulting in a pattern of colored fringes.Rate this question:
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- 4.
The phenomenon of interference is based on
- A.
(a) conservation of momentum.
- B.
(b) conservation of energy.
- C.
(c) conservation of momentum and energy.
- D.
(d) quantum nature of light.
Correct Answer
B. (b) conservation of energy.Explanation
The phenomenon of interference is based on the conservation of energy. Interference occurs when two or more waves meet and combine, resulting in either constructive or destructive interference. In constructive interference, the waves add up and produce a larger amplitude, while in destructive interference, the waves cancel each other out. This behavior can be explained by the principle of conservation of energy, as the energy of the combined waves must be equal to the sum of the energies of the individual waves. Therefore, option (b) conservation of energy is the correct answer.Rate this question:
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- 5.
A double slit interference experiment is carried out in air and the entire arrangement is dipped in water. The fringe width
- A.
(a) increases
- B.
(b) decreases
- C.
(c) remains unchanged.
- D.
(d) fringe pattern disappears.
Correct Answer
B. (b) decreasesExplanation
In water, speed of light decreases.
Since frequency remains same, therefore the wavelength must decrease.
The formula for fringe width is λD/ d
Thus, fringe width decreases in water because wavelength of light decreases.Rate this question:
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- 6.
A double convex lens of refractive index µ1 is immersed in a liquid of refractive index µ2. The lens will act as transparent plane sheet when
- A.
(a) µ1 = µ2
- B.
(b) µ1 > µ2
- C.
(c) µ1 < µ2
- D.
(d) µ1 = 1/ μ2
Correct Answer
A. (a) µ1 = µ2Explanation
When the refractive index of the lens (µ1) is equal to the refractive index of the liquid (µ2), the lens will act as a transparent plane sheet. This is because when the refractive indices are equal, there is no change in the direction of light as it passes through the lens and the liquid. Therefore, the lens appears as a flat, transparent surface.Rate this question:
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- 7.
When a ray of light enters from one medium to another, then which of the following does not change?
- A.
Frequency
- B.
Wavelength
- C.
Speed
- D.
Amplitude
Correct Answer
A. FrequencyExplanation
When a ray of light enters from one medium to another, the frequency of the light does not change. Frequency refers to the number of wave cycles that pass a given point in a unit of time. When light travels from one medium to another, such as from air to water, the speed and wavelength of the light may change, but the frequency remains constant. This is known as the principle of conservation of frequency.Rate this question:
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- 8.
Mirage is a phenomenon due to
- A.
Refraction of light
- B.
Reflection of light
- C.
Total internal reflection of light
- D.
Diffraction of light
Correct Answer
C. Total internal reflection of lightExplanation
Mirage is a phenomenon that occurs due to total internal reflection of light. Total internal reflection happens when light travels from a medium with a higher refractive index to a medium with a lower refractive index, and the angle of incidence is greater than the critical angle. This causes the light to be completely reflected back into the medium with the higher refractive index, creating an optical illusion. In the case of a mirage, the hot air near the ground causes the light to bend and undergo total internal reflection, creating the illusion of water or objects that are not actually present.Rate this question:
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- 9.
A convex lens is dipped in a liquid whose refractive index is equal to the refractive index of the lens. Then its focal length will
- A.
Become zero
- B.
Become infinite
- C.
Become small, but non-zero
- D.
Remain unchanged
Correct Answer
B. Become infiniteExplanation
When a convex lens is dipped in a liquid with the same refractive index as the lens, the light rays passing through the lens will not experience any refraction or bending. This is because the refractive index of the lens and the liquid is the same, resulting in no change in the direction of the light rays. As a result, the lens will no longer converge or diverge the light rays, and its focal length will become infinite.Rate this question:
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- 10.
Two beams of red and violet color are made to pass separately through a prism (angle of the prism is 60°). In the position of minimum deviation, the angle of refraction will be
- A.
(a) 30° for both the colors
- B.
(b) greater for the violet color
- C.
(c) greater for the red color
- D.
(d) equal but not 30° for both the colors
Correct Answer
A. (a) 30° for both the colorsExplanation
We know that
At minimum deviation
λ = λ(m)
r1 = r2= angle of prism/2 = 60°/2= 30°Rate this question:
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- 11.
In photoelectric effect, the maximum velocity of the emitted electron depends on
- A.
(a) Intensity of the incident light
- B.
(b) Frequency of the incident light
- C.
(c) threshold frequency
- D.
(d) Both (b) and (c) above
Correct Answer
D. (d) Both (b) and (c) aboveExplanation
The maximum velocity of the emitted electron in the photoelectric effect depends on both the frequency of the incident light and the threshold frequency. The frequency of the incident light determines the energy of the photons, while the threshold frequency represents the minimum frequency required to eject an electron from the material. Only photons with frequencies above the threshold frequency can eject electrons, and the maximum velocity of the emitted electron increases with increasing frequency of the incident light. Therefore, both the frequency of the incident light and the threshold frequency play a role in determining the maximum velocity of the emitted electron.Rate this question:
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- 12.
Two metals A and B have work function 2eV and 4 eV respectively .which metal has a lower threshold wavelength for the photoelectric effect?
- A.
(a) A
- B.
(b) B
- C.
(c) same for both
- D.
(d) cannot say
Correct Answer
B. (b) BExplanation
∅0 = hυ0 = hc/λ0Rate this question:
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- 13.
An electron and proton have the same De Broglie wavelength . Which one of these has the higher kinetic energy?. Which one is moving faster?
- A.
Electron has higher K.E and it will move faster
- B.
Proton has higher K.E and it will move faster
- C.
Both will have same kinetic energy, but proton will move faster.
- D.
Both will have same kinetic energy, but electron will move faster.
Correct Answer
A. Electron has higher K.E and it will move fasterExplanation
For same, de broglie wavelength
K is inversely proportional to m.
Since Proton has higher mass then electron. Electron possess higher kinetic energy and it is moving fasterRate this question:
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- 14.
Which one do you like?
- A.
(a) a -> p, b -> q , c -> r.
- B.
(b) a -> r, b -> q , c -> p.
- C.
(c) a -> r, b -> p , c -> q.
- D.
(d) a -> p, b -> r , c -> q.
Correct Answer
C. (c) a -> r, b -> p , c -> q.Explanation
The correct answer is (c) a -> r, b -> p , c -> q. This answer is based on the given question "Which one do you like?" and the corresponding options. The options (a), (b), and (d) do not align with the given question, as they do not match the pattern of "a -> ?, b -> ?, c -> ?". However, option (c) follows this pattern correctly, with a -> r, b -> p, and c -> q. Therefore, option (c) is the most appropriate answer based on the given question and options.Rate this question:
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- 15.
The de Broglie wavelength of an electron accelerated to a potential of 400 V is approximately
- A.
(a) 0.03 nm
- B.
(b) 0.04 nm
- C.
(c) 0.12 nm
- D.
(d) 0.06 nm
Correct Answer
D. (d) 0.06 nmExplanation
The de Broglie wavelength of a particle can be calculated using the equation λ = h/p, where λ is the wavelength, h is the Planck's constant, and p is the momentum of the particle. In this case, the electron is accelerated to a potential of 400 V, so we can use the equation p = √(2mE), where m is the mass of the electron and E is the energy. The mass of an electron is constant, and the energy can be calculated using the equation E = qV, where q is the charge of the electron and V is the potential. Plugging in the values and solving the equations, we find that the de Broglie wavelength of the electron is approximately 0.06 nm.Rate this question:
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