JPJC 2026 Wave Motion Tutorial

2026/JPJC/PHYSICS/9478 1 JURONG PIONEER JUNIOR COLLEGE 9478 H2 PHYSICS WAVE MOTION TUTORIAL Self-Check Questions S1 Explain what is meant by the term progressive as applied to a wave. S2 Define the displacement, amplitude, period, frequency, wavelength and speed of a wave. S3 Explain the term phase difference. S4 Explain what is meant by a wavefront. S5 A wave of frequency f and wavelength  has speed v. Using the definition of speed, deduce the equation for speed of the wave. S6 (a) Define the intensity of a wave. (b) State the relationship between the intensity and the amplitude of a wave. (c) State the relationship between intensity and distance from a point source. S7 Distinguish between longitudinal and transverse waves. S8 Polarisation is a phenomenon associated with transverse waves and not longitudinal waves. Discuss. Self-Practice Questions 1 A progressive wave can be represented by the following graphs. What gives the speed of the wave? A pq B p q C q p D 1 pq

2026/JPJC/PHYSICS/9478 2 2 [N03/P3/Q3(b)] modified Fig. 2.1 and 2.2 show two graphs for the same wave. Fig. 2.1 Fig. 2.2 Calculate the speed of the wave. 3 The graph shows the shape at a particular instant of part of a transverse wave travelling along a string. Which statement about the motion of points along the string is correct? A The speed of point P is a maximum. B The energy of point R is entirely kinetic. C The acceleration of point T is a maximum. D The displacement of point Q is always zero. 4 Referring to the same diagram in Q3, which statement is correct? A The periodic time is represented by the length PT. B The particles Q and S have the same velocity. C The particles R and T are in phase. D The amplitude of the wave is the vertical separation RT. E The length QS is half a wavelength. displacement distance along string displacement / mm 4 1.8 0.2 0.6 0.4 0.8 2.0 1.0 2.2 1.2 1.4 1.6 2.4 2.6 distance / m 4 displacement / mm time / ms 2 4 8 10 12 14 16 18 20 6

2026/JPJC/PHYSICS/9478 3 5 A transverse progressive wave travels along a rope. The graph shows the variation of displacement with distance along the rope, at a certain time. The wave is travelling to the right. In which direction are P and Q moving? movement of P movement of Q A upwards upwards B upwards downwards C downwards upwards D downwards downwards 6 Visible light has wavelengths between 400 nm (blue) and 700 nm (red). Determine the maximum frequency of visible light. 7 A transverse wave is passed through a piece of polarising material. The resulting amplitude of the wave is a. The polarising material is now rotated through angle  and the amplitude of the wave becomes cosa  . The new intensity of the transmitted wave is proportional to A cosa  B 2cosa  C 2 cosa  D 22cosa  8 A sheet of glass transmits 70% of the energy of the incident light. What is the value of the quantity amplitude of the transmitted light amplitude of the incident light ? A 0.49 B 0.70 C 0.84 D 1.19 Answer Key 1 C 2 320 m s-1 3 C 4 E 5 B 6  147.50 10 Hz 7 D 8 C

2026/JPJC/PHYSICS/9478 4 Discussion Questions 1 Fig. 1.1 shows a transverse wave at a particular instant. The wave is travelling to the right. The frequency of the wave is 12.5 Hz. Fig. 1.1 At the instant shown, the displacement is zero at the point P. Determine the shortest time to elapse before the displacement is zero at point Q. 2 Transverse progressive sinusoidal waves of wavelength  are passing vertically along a horizontal rope. P and Q are points on the rope 3 2  apart and the waves are trave lling from P to Q. Which row correctly describes Q at an instant when P is displaced upwards but is moving downwards? displacement of Q movement of Q A upwards downwards B upwards upwards C downwards upwards D downwards downwards 3 A circular bowl of diameter 400 mm contains water at rest. If the side of the bowl is tapped gently, a completely circular pulse can be produced on the surface of the water , which travels inwards with a speed of 250 mm s −1 . Determine the radius of the pulse and its direction of travel 1 .0 s after the pulse is produced. 4 A point source of sound radiates energy uniformly in all directions. At a distance 3.0 m from the source, the amplitude of vibration of air molecules is 71.0 10 m− . Assuming that no sound energy is absorbed, calculate the amplitude of vibration 5.0 m from the source. 5 A point source of sound emits energy equally in all directions at a constant rate and a man 8.0 m from the source listens. After a while, the intensity of the source is halved. If the man still wishes the sound to seem as loud as before, determine how far he should be from the source. 6 A microphone of cross -sectional area 0.80 cm 2 is placed in front of a small speaker emitting 3.0 W of sound output. The distance between the microphone and the speaker is 2.0 m. Determine the amount of energy the microphone receives in 5.0 s.

2026/JPJC/PHYSICS/9478 5 7 [N02/P3/Q6(b)(part)] A satellite passing the planet Neptune communicates with its controller on the Earth using a microwave transmitter with output power 22.0 W and wavelength 79600 m. Neptune is 124.35 10 m from the Earth ’s surface at the time when the communication takes place. (a) State whether microwaves are longitudinal or transverse, and describe evidence for your claim. (b) Calculate the time taken for a signal to travel from the satellite to the Earth. (c) Assuming that the power transmitted by the satellite is radiated uniformly in all directions, calculate the power received on Earth by a dish aerial of effective area 260 m 2 . (d) The actual power received at the dish aerial is 151.2 10 W− . Suggest why the actual power received is greater than that calculated in (c). 8 [N03/P3/Q4 (part)] Fig. 8.1 shows a displacement-distance graph for two sound waves A and B, of the same frequency and amplitude. Wave A is travelling to the right and wave B is travelling to the left. Fig. 8.1 (a) Use Fig. 8.1 to deduce the phase differen ce between the two waves at the instant shown. (b) Fig. 8.1 has the disadvantage that it makes the sound waves appear to be transverse waves, when they are not. (i) What type of wave is sound? (ii) Explain why sound waves cannot be polarised. (c) The waves in Fig. 8.1 have a frequency of 484 Hz. Deduce their speed to three significant figures.

2026/JPJC/PHYSICS/9478 6 9 A certain camera lens uses two polarising filters to decrease the intensity of light entering the camera. The light intensity in the scene is 20 W m−2. (a) Determine the intensity of the light between the two filters. (b) If the light intensity at the image sensor of the camera is 3 W m−2, determine the angle between the transmission axis of the polarisers. 10 A beam of natural light falls on a system of 6 polaroids. The polaroids are arranged in succession such that each polaroid is turned through 30  with respect to the preceding one. Determine the fraction of the incident intensity that passes through the system? Show your working clearly. 11 A plane wave of amplitude A is incident on a surface of area S placed so that it is perpendicular to the direction of travel of the wave. The energy per unit time intercepted by the surface is E. If the amplitude of the wave is increased to 2 A and the surface area is reduced to 2 S , determine the amount of energy per unit time that is intercepted by this surface. (Express your answer in terms of E.) Answers: 1 0.0100 s 8(a) 1.57 rad 3 50 m