WavesIB MYP Physics: Topic test

1. 1
   A student in Delhi and her partner hold the two ends of a long spring (a slinky) stretched along a smooth floor. She pushes and pulls one end back and forth along the length of the spring, and a pattern of squashed and stretched coils travels to her partner. She then shakes the end from side to side across the spring, and a different kind of wave travels along it.

   (a)

   What is transferred from one end of the spring to the other by the waves?

   [1 mark]

   • AEnergy only
   • BBoth the coils and energy
   • CThe coils only
   • DThe frequency only

   (b)

   The student makes 8 complete pushes and pulls in 4.0 s. What is the frequency of the wave?

   [1 mark]

   • A0.50 Hz
   • B32 Hz
   • C2.0 Hz
   • D4.0 Hz

   (c)

   Describe the difference between a transverse wave and a longitudinal wave and give one example of each.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A simple periscope contains two right-angled glass prisms. Light enters the first prism along the normal to its face, hits the long sloping side at an angle of incidence of 45° and is turned through 90°. The critical angle of the glass is 42°.

   (a)

   Why is the light totally internally reflected at the sloping side?

   [1 mark]

   • AThe angle of incidence is smaller than the critical angle
   • BThe light speeds up as it reaches the sloping side
   • CThe light is travelling from air into glass
   • DThe angle of incidence is greater than the critical angle and the light is travelling from glass towards air

   (b)

   What happens to the light as it enters the first prism along the normal?

   [1 mark]

   • AIt speeds up and bends away from the normal
   • BIt slows down but does not change direction
   • CIt keeps the same speed and does not change direction
   • DIt slows down and bends towards the normal

   (c)

   In a test, a ray of light passes from air into a block of this glass. The angle of incidence is 50° and the angle of refraction is 31°. Calculate the refractive index of the glass. Give your answer to two significant figures.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A fishing boat off the coast of Norway uses sonar. It sends a pulse of ultrasound of frequency 50 kHz straight down to the sea bed and detects the echo 0.080 s later. Sound travels at 1500 m/s in sea water.

   (a)

   Calculate the depth of the sea at this point.

   [3 marks]

   (b)

   Calculate the wavelength of the ultrasound in sea water. Explain why a diver in the water cannot hear the pulse.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Water waves move towards a beach in Portugal. In deep water the waves have a frequency of 0.25 Hz and a wavelength of 12 m. Near the beach the water is shallow and the waves travel more slowly, at 1.5 m/s. The waves meet the boundary between deep and shallow water at an angle. To check the speed in the shallow water, a student times a wave crest as it moves between two posts 18 m apart. She starts a stopwatch as the crest passes the first post and stops it as the crest passes the second post. Her time is 12.4 s. She takes this reading once.

   (a)

   Calculate the speed of the waves in deep water and their wavelength in shallow water. Explain why the waves change direction at the boundary.

   [6 marks]

   (b)

   Evaluate the student's measurement of the speed of the waves in the shallow water.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   Two loudspeakers stand side by side in a school hall in Warsaw. Both play exactly the same steady note from one signal generator. A student walks slowly along a line in front of them and finds that the sound is loud at some places and almost silent at others.

   (a)

   What causes the loud places?

   [1 mark]

   • AWaves from the two speakers cancel each other
   • BSound reflects from the back wall of the hall
   • CWaves from the two speakers arrive in step, with crests meeting crests
   • DThe sound is diffracted through a narrow gap

   (b)

   What happens at a place where the sound is almost silent?

   [1 mark]

   • AA crest from one speaker meets a trough from the other, so the waves cancel
   • BThe waves from the two speakers travel at different speeds
   • CCrests meet crests, so the waves add together
   • DThe floor absorbs all the sound

   (c)

   Explain why the quiet places disappear when one of the speakers is switched off.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   A jeweller in Jaipur examines a gemstone through a converging lens of focal length 5.0 cm. She holds the lens 3.0 cm from the gem. A photographer nearby uses a camera that also contains a converging lens.

   (a)

   What kind of image does the jeweller see?

   [1 mark]

   • AReal, inverted and smaller
   • BVirtual, upright and magnified
   • CReal, inverted and magnified
   • DVirtual, inverted and smaller

   (b)

   Which describes the image that the camera lens forms on its sensor when it photographs a distant object?

   [1 mark]

   • AVirtual, upright and magnified
   • BVirtual, upright and smaller
   • CReal, upright and magnified
   • DReal, inverted and smaller

   (c)

   Explain why the gem must be closer to the lens than 5.0 cm for the lens to work as a magnifying glass.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A television screen in an electronics shop in Johannesburg makes every colour by mixing light from tiny red, green and blue lamps. A shop assistant holds a green plastic leaf in front of the screen. At first the screen shows white light.

   (a)

   State the colour seen when the screen mixes light from (i) red and green lamps, (ii) green and blue lamps, (iii) red, green and blue lamps at full brightness.

   [3 marks]

   (b)

   Explain why the leaf looks green in white light. The screen then changes to show only red light. State the colour the leaf now looks and explain why.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A mobile phone company wants to build a mast on the roof of a school in a village in rural Kenya. The mast would send and receive signals using microwaves of frequency 2.1 × 10⁹ Hz. Many parents want better phone coverage so that they can call for medical help. Some parents worry that the microwaves could harm their children's health.

   (a)

   Calculate the wavelength of the microwaves. Explain why the signals reach phones almost instantly and why microwaves are considered less harmful than X-rays.

   [6 marks]

   (b)

   Discuss whether the school should allow the company to build the mast.

   [6 marks]

   Total for question 8: 12 marks

End of questions