HCI Worksheet 15 Waves (answers)

Hwa Chong Institution Sec 3 Physics 1 Name: _________________________________________ Class: ___________ Date: ______________ Sec 3 Physics Worksheet 15: Waves 1 Water waves were produced in a ripple tank using a vibrator of frequency 3 Hz. Which of the following values of speed and wavelength could the waves have had? speed wavelength A 1 cm/s 3 cm B 2 cm/s 1 cm C 5 cm/s 15 cm D 12 cm/s 4 cm [ ] 2 A wave source of frequency 1000 Hz emits waves of wavelength 0.1m. How long does it take for the waves to travel 2500 m? A 4 s C 40 s B 25 s D 100 s [ ] 3 The table shows examples of transverse and longitudinal waves. Which line in the table is correct? transverse longitudinal A gamma rays sound B infra-red radio C infra-red water waves D radio light [ ] 4 The diagram shows a ball floating in a tank of water. Which diagram shows the movement of the ball when the wave passes? [ ]

Hwa Chong Institution Sec 3 Physics 2 5 A long rope is stretched out on the floor. One end of the rope is then shaken. The graph shows the rope at a particular moment in time. Which is the wavelength of the wave motion? A 0.36 m C 0.8 m B 0.6 m D 1.6 m [ ] 6 The diagram shows how displacement varies with time as a wave passes a fixed point. What is the frequency of this wave? A 0.25 Hz C 1.0 Hz B 0.50 Hz D 2.0 Hz [ ] 7 The diagram shows a cross -section of a water wave. Which distance is the amplitude of the wave? [ ] E

Hwa Chong Institution Sec 3 Physics 3 8 A lightly coiled spring is fixed at one end and held by hand at the other. Which hand movements cause first a compression and then a rarefaction to travel along the spring? A down then up B up then down C left then right D right then left [ ] 9 A transverse wave travels from left to right. The diagram below shows how, at a particular inst ant of time, the displacement of particles in the medium varies with position. Which arrow represents the direction of the velocity of the particle marked P? [ ] 10 Light travels from air into glass as shown below.

Hwa Chong Institution Sec 3 Physics 4 What is the refractive index of glass? A B C D [ ] 11 Which of the following electromagnetic waves has a frequency greater than that of visible light? A Ultraviolet B Radio C Microwaves D Infrared [ ] 12 A particle oscillates with simple harmonic motion with period T. At time t = 0, the particle has its maximum displacement. Which graph shows the variation with time t of the kinetic energy Ek of the particle? [ ] S P sin sin R Q sin sin R P sin sin S Q sin sin

Hwa Chong Institution Sec 3 Physics 5 13 The graph shows measurements of the height h of sea level at different times t in the Bay of Fundy. Which of the following gives the approximate amplitude and period of the tides? Amplitude Period A 6.5 m 6 hours B 13 m 12 hours C 6.5 m 12 hours D 13 m 6 hours [ ] 14 Which of the following is a value of wavelength that is found in the visible region of the electromagnetic spectrum? A 4 × 10 –5 m B 4 × 10 –7 m C 4 × 10 –9 m D 4 × 10 –11 m [ ] 15 Two waves meet at a point in space. Which of the following properties always add together? A Displacement B Amplitude C Speed D Frequency [ ]

Hwa Chong Institution Sec 3 Physics 6 16 The diagram below is a snapshot of wave fronts of circular waves emitted by a point source S at the surface of water. The source vibrates at a frequency f = 10.0 Hz. The speed of the wave front is A 0.15 cm s –1 . B 1.5 cm s –1 . C 15 cm s –1 . D 30 cm s –1 . [ ] 17 Two coherent point sources S1 and S2 emit spherical waves.

Hwa Chong Institution Sec 3 Physics 7 Which of the following best describes the intensity of the waves at P and Q? P Q A maximum minimum B minimum maximum C maximum maximum D minimum minimum [ ] 18 Monochromatic light travels from air into water. Which of the following describes the changes in wavelength and speed? Wavelength Speed A increases decreases B increases increases C decreases increases D decreases decreases [ ] 19 A wave pulse is travelling to the right along a string. Which of the following best represents the direction of the velocity of the point P? A ↑ B ↓ C → D ← 1 D 2 B 3 B 4 D 5 D 6 B 7 C 8 D 9 C 10 D 11 A 12 C 13 C 14 B 15 A 16 C 17 A 18 D 19 B

Hwa Chong Institution Sec 3 Physics 8 STRUCTURED QUESTIONS 1 The figure below shows a student setting up waves on a long elastic cord. The student's hand makes one complete up -and-down movement in 0.40s, and in each up -and-down movement the hand moves through a height of 0.30 m. The wavelength of the waves on the string is 0.80 m. For this wave, determine a Amplitude = 0.15 m b Period = 0.40 s c Frequency = 2.5 Hz d Speed = 2.0 ms-1 [6] e Using a line with arrows on both ends, label the wavelength of the waves in the diagram above. [1] f Label 2 points Y and Z on the line which is in phase with point X. [2] g Sketch the shape of the waves in real life. [2] Graph with decreasing amplitude. (A common mistake is to draw the wavelength getting shorter as amplitude decreases. The wavelength should be relatively constant. Can you think of a reason?) Explanation: Energy losses as the waves propagates. 2 Transverse waves are produced in a long rope by securing one end of th e rope to a wall and then moving the other end from side to side by hand. The frequency of the waves is 2 Hz. a How are “transverse waves” different from “longitudinal waves”? Transverse waves travel (or propagate) in a direction perpendicular to the direction of vibrations; longitudinal waves travel in a direction parallel to the direction of vibrations. 0.30 m X (f) Z (f) Y e) 0.80 m

Hwa Chong Institution Sec 3 Physics 9 b Explain the meaning of the expression "the frequency is 2 Hz". The waves produce two complete vibrations in one second. [1] c What determines the amplitude of the waves produced? The amplitude of the oscillating hand determines the amplitude of the waves. (The larger the hand swing, the larger the amplitude of the wave) [1] 3 Transverse waves of wavelength 40 mm and amplitude 15 mm travel across a liquid surface. a On the grid (2mm) below draw a full-scale diagram showing a side view of the liquid surface at a particular instant. [2] b If the frequency of vibrations of the waves is 12 Hz, calculate the speed at which they travel across the liquid surface. v = f = 12 x (40/1000) = 0.48 ms-1 (2 sf) Speed = ……………………………….. mm s-1 [2] 40 mm 15 mm

Hwa Chong Institution Sec 3 Physics 10 4 a Figure 4.1 shows the graph of the variation of the displacement of a wave with distance along the wave at a particular time. Figure 4.1 State the values for (i) the amplitude of the wave: 0.6 m [1] (ii) the wavelength of the wave: 5 m [1] b Figure 4.2 shows the graph of the variation of the displacement of the same wave with time at a particular point along the wave. Figure 4.2 State values for (i) Time for one cycle = 1.25 s [1] (ii) Frequency of the wave = 0.800 Hz [1] c Calculate the speed of the wave drawn in Figures 4.1 and 4.2.