8.3. Interference
A subsection of Physics, 9702, through 8. Superposition
Listing 10 of 90 questions
Light from a laser is used to produce an interference pattern on a screen, as shown in . light of wavelength 660 nm O P Q R 0.44 mm 1.8 m double slit screen central bright fringe dark fringe bright fringe dark fringe (not to scale) The light of wavelength 660 nm is incident normally on two slits that have a separation of 0.44 mm. The double slit is parallel to the screen. The perpendicular distance between the double slit and the screen is 1.8 m. The central bright fringe on the screen is formed at point O. The next dark fringe below point O is formed at point P. The next bright fringe and the next dark fringe below point P are formed at points Q and R respectively. The light waves from the two slits are coherent. State what is meant by coherent. For the two light waves superposing at R, calculate: the difference in their path lengths, in nm, from the slits path difference = nm their phase difference. phase difference = ° Calculate the distance OQ. distance OQ = m The intensity of the light incident on the double slit is increased without changing the frequency. Describe how the appearance of the fringes after this change is different from, and similar to, their appearance before the change. The light of wavelength 660 nm is now replaced by blue light from a laser. State and explain the change, if any, that must be made to the separation of the two slits so that the fringe separation on the screen is the same as it was for light of wavelength 660 nm.
9702_s22_qp_22
THEORY
2022
Paper 2, Variant 2
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An electromagnetic wave in a vacuum has a wavelength of 8.4 × 10–6 m. State the name of the principal region of the electromagnetic spectrum for the wave. Calculate the frequency, in THz, of the wave. frequency = THz An arrangement that uses a double slit to demonstrate the interference of light from a laser is shown in . light, wavelength 6.2 × 10–7 m double slit screen 2.8 m a (not to scale) The light from the laser has a wavelength of 6.2 × 10–7 m and is incident normally on the slits. The separation of the two slits is a. The slits and screen are parallel and separated by a distance of 2.8 m. An interference pattern of bright fringes and dark fringes is formed on the screen. The distance on the screen across 8 bright fringes is 22 mm, as illustrated in . P Q 22 mm bright fringe dark fringe R The light waves emerging from the two slits are coherent. State what is meant by coherent. Calculate the separation a of the slits. a = m Fringe P is the central bright fringe of the interference pattern in . Fringe Q and fringe R are the nearest dark fringe and the nearest bright fringe respectively to the right of fringe P, as shown in . Calculate the difference in the distances (the path difference) from each slit to the centre of fringe Q. difference in the distances = m State the phase difference between the light waves meeting at the centre of fringe R. phase difference = °
9702_s23_qp_21
THEORY
2023
Paper 2, Variant 1
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In order that interference between waves from two sources may be observed, the waves must be coherent. Explain what is meant by interference, coherence. Red light of wavelength 644 nm is incident normally on a diffraction grating having 550 lines per millimetre, as illustrated in . Red light of wavelength λ is also incident normally on the grating. The first order diffracted light of both wavelengths is illustrated in . incident light diffraction grating wavelengths 644 nm and 1st order, wavelength 644 nm 1st order, wavelength 1st order, wavelength 644 nm zero order 1st order, wavelength [T Calculate the number of orders of diffracted light of wavelength 644 nm that are visible on each side of the zero order. number = ………………………… State and explain 1. whether λ is greater or smaller than 644 nm, 2. in which order of diffracted light there is the greatest separation of the two wavelengths. .
9702_w06_qp_2
THEORY
2006
Paper 2, Variant 0
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Use shows the variation with time t of the displacement y of a wave W as it passes a point P. The wave has intensity I. y t wave W A second wave X of the same frequency as wave W also passes point P. This wave has intensity  I. The phase difference between the two waves is 60°. On , sketch the variation with time t of the displacement y of wave X. In a double-slit interference experiment using light of wavelength 540 nm, the separation of the slits is 0.700 mm. The fringes are viewed on a screen at a distance of 2.75 m from the double slit, as illustrated in (not to scale). coherent light wavelength 540 nm 0.700 mm 2.75 m screen Examiner’s Use Calculate the separation of the fringes observed on the screen. separation = mm State the effect, if any, on the appearance of the fringes observed on the screen when the following changes are made, separately, to the double-slit arrangement in . The width of each slit is increased but the separation remains constant. The separation of the slits is increased.
9702_w07_qp_2
THEORY
2007
Paper 2, Variant 0
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11 In modern communications systems, the majority of data is transmitted in digital form rather than analogue form. Suggest three advantages of the transmission of data in digital form. 1. 2. 3. A recording is made of some music. For this recording, the music is sampled at a rate of 44.1 kHz and each sample consists of a 16-bit word. Suggest the effect on the quality of the recording of 1. sampling at a high frequency rather than a lower frequency, 2. using a long word length rather than a shorter word length. The recording lasts for a total time of 5 minutes 40 seconds. Calculate the number of bits generated during the recording. number =
9702_w12_qp_41
THEORY
2012
Paper 4, Variant 1
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12 Wire pairs used for the transmission of telephone signals are subject to cross-linking. Explain what is meant by cross-linking. Suggest why cross-linking in coaxial cables is much less than in wire pairs. A wire pair has a length of 1.4 km and is connected to a receiver, as illustrated in . 1.4 km receiver input signal power 3.0 × 10–3 W wire pair constant noise power 3.8 × 10–8 W The constant noise power in the wire pair is 3.8 × 10–8 W. For an input signal to the wire pair of 3.0 × 10–3 W, the signal-to-noise ratio at the receiver is 25 dB. Calculate the attenuation per unit length for the wire pair. attenuation per unit length = dB km–1
9702_w12_qp_41
THEORY
2012
Paper 4, Variant 1
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11 In modern communications systems, the majority of data is transmitted in digital form rather than analogue form. Suggest three advantages of the transmission of data in digital form. 1. 2. 3. A recording is made of some music. For this recording, the music is sampled at a rate of 44.1 kHz and each sample consists of a 16-bit word. Suggest the effect on the quality of the recording of 1. sampling at a high frequency rather than a lower frequency, 2. using a long word length rather than a shorter word length. The recording lasts for a total time of 5 minutes 40 seconds. Calculate the number of bits generated during the recording. number =
9702_w12_qp_42
THEORY
2012
Paper 4, Variant 2
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12 Wire pairs used for the transmission of telephone signals are subject to cross-linking. Explain what is meant by cross-linking. Suggest why cross-linking in coaxial cables is much less than in wire pairs. A wire pair has a length of 1.4 km and is connected to a receiver, as illustrated in . 1.4 km receiver input signal power 3.0 × 10–3 W wire pair constant noise power 3.8 × 10–8 W The constant noise power in the wire pair is 3.8 × 10–8 W. For an input signal to the wire pair of 3.0 × 10–3 W, the signal-to-noise ratio at the receiver is 25 dB. Calculate the attenuation per unit length for the wire pair. attenuation per unit length = dB km–1
9702_w12_qp_42
THEORY
2012
Paper 4, Variant 2
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Questions Discovered
90