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Wave Systems · Part 2 of 3
9 exam-style questions with model answers, plus 12 quick multi-choice questions — every question on this part of the standard, grouped by the 3 pages of notes they come from.
Write a full answer before you reveal the model one. That comparison is where the learning happens.
In a two-slit interference experiment, waves arriving at a point on the screen have a path difference of exactly two wavelengths.
State whether a bright or a dark fringe is observed at this point, and give a reason.
A two-slit interference pattern is produced using a laser.
Explain why a bright fringe always appears at the centre of the pattern, and explain why the two slits must be illuminated by the same laser rather than by two separate lasers.
Two loudspeakers m apart are driven by the same signal generator at Hz (speed of sound m s−1). A student walks along a line parallel to the speakers and m away from them, and hears the loudness rise and fall.
Explain fully what determines the positions of the loud and quiet points. Then discuss what would happen to the pattern if (a) the frequency were doubled and (b) one speaker were disconnected, and explain what happens to the sound energy at the quiet positions.
In a two-slit experiment, the slits are mm apart, the screen is m away, and the fringe spacing is mm.
Calculate the wavelength of the light.
Light of wavelength nm passes through two slits mm apart onto a screen m away.
Calculate the distance from the central bright fringe to the third bright fringe. Then state and explain what would happen to this distance if the slit separation were halved.
A student performs a two-slit experiment using a white-light source instead of a laser. They observe a white central fringe, with coloured fringes either side that become increasingly smeared and overlapping further from the centre, until the pattern washes out entirely.
Explain fully why the central fringe is white, why the outer fringes are coloured, and why the pattern eventually washes out. Support your answer with a calculation comparing red ( nm) and blue ( nm) light for slits mm apart on a screen m away.
A diffraction grating has lines per millimetre.
Calculate the grating spacing in metres.
Light of wavelength nm falls on a grating with lines per millimetre.
Calculate the angle of the second-order maximum, and explain why the maxima produced by a grating are sharper than those from a pair of slits.
White light is shone through a diffraction grating with lines per millimetre. Instead of white fringes, a series of continuous spectra is seen either side of a white central maximum.
Explain fully why this happens, and calculate the angular width of the first-order spectrum (taking visible light as nm to nm). Determine whether the first- and second-order spectra overlap, showing your reasoning.