Physics 2000 JAMB Past Questions - Question 13: Coherence II. Same frequency III. Same wavelength IV. Same intensity Which of the conditions above are necessary to produce interference fringes?

Correct Answer

B

Explanation

Interference fringes are a characteristic phenomenon that occurs when two or more coherent waves overlap and interact. To produce interference fringes, the following conditions are necessary:The conditions necessary to produce interference fringes are:

I. Coherence
II. Same frequency
III. Same wavelength

Explanation:

I. Coherence: Coherence refers to the property of waves being in phase or having a constant phase relationship. In order to produce interference fringes, the waves from different sources or parts of the same source must be coherent. This means that the phase difference between the waves should remain constant over time.

II. Same frequency: Interference occurs when waves of the same frequency superpose or combine. If the waves have different frequencies, they will not interfere constructively or destructively to produce fringes.

III. Same wavelength: Interference fringes are formed when waves of the same wavelength overlap and interfere with each other. If the waves have different wavelengths, they will not produce the characteristic pattern of constructive and destructive interference.

IV. Same intensity: The intensity of the waves does not directly affect the formation of interference fringes. Interference fringes can still be observed even if the intensities of the waves are different. However, the relative intensities of the interfering waves can affect the visibility or contrast of the fringes.

Therefore, the necessary conditions to produce interference fringes are coherence, same frequency, and same wavelength.

I. Coherence: The sources of the waves must be coherent, meaning that they have a constant phase relationship. This ensures that the waves maintain a consistent phase difference between them, allowing them to interfere constructively and destructively.

III. Same wavelength: The interfering waves must have the same wavelength. If the wavelengths are different, the interference pattern will be irregular and not result in well-defined fringes.

The condition "Same frequency" (II) is not necessary for the production of interference fringes. While having the same frequency often accompanies waves with the same wavelength, it's the wavelength that directly determines the spacing and characteristics of the interference fringes.

The condition "Same intensity" (IV) is also not necessary for the production of interference fringes. Interference fringes can occur with waves of different intensities. The intensity of the fringes may vary, but the interference pattern itself is determined primarily by the phase relationship and wavelength of the waves.

So, the necessary conditions for producing interference fringes are I (Coherence) and III (Same wavelength).