HCI Worksheet 4 EM waves (printable version)

Hwa Chong Institution Sec 3 (Physics) 1 Name: __________________________________________ Class: __________ Date: ______________ Sec 3 Physics Worksheet 4: EM waves (self-attempt) Conceptual Questions 1. What colour of the visible spectrum has the longest wavelength? Which has the shortest wavelength? 2. In a boutique store with only fluorescent lighting, a customer insists on taking dresses into the daylight at the doorway to check their colour. Is she reasonable? Explain. 3. Fire engines used to be red. Yellow-green is now the preferred colour. Why? 4. Which EM waves are associated with high-energies? Which ones are the low-energies? 5. Does a microwave photon have a lot of energy? How can our food be “cooked” by microwaves? 6. Can radar cook birds which happen to fly by during its operation? 7. Human beings have a body temperature of around 37oC. What is the dominant EM radiation that our bodies emit? 8. Can the human body produce EM waves other than infrared? 9. Does light travel infinitely fast, or does it have a finite speed? 10. Can we look into the past? 11. Is Earth a bright object in the solar system? 12. There is a rule (Wien’s displacement law) that tells us the type of radiation an object emits depends on its temperature. Cool objects emit radio waves mostly, while very hot objects (e.g. plasma of about 10 million K) emit mostly X-rays. Therefore, by looking at the colour of stars, we can tell how hot the star surfaces are. There are red stars, orange stars, yellow stars, blue stars and white stars. Why are there no green stars?

Hwa Chong Institution Sec 3 (Physics) 2 SECTION A MULTIPLE CHOICE QUESTIONS 1 A VHF radio station broadcasts at a frequency of 90 MHz (9.0 x 107 Hz). The speed of radio waves is 3.0 x 108 m/s. What is the wavelength of the waves broadcast by the station? A 0.30 m C 6.0 m E 27 x 1015 m B 3.3 m D 12 x 1015 m [ ] 2 Which of the following properties applies to X-rays, γ-rays, infra-red, ultra-violet and visible light? A They are all damaging to health. B They all have similar wavelengths. C They all travel at the same speed in a vacuum. D They are all affected by magnetic fields. E They can all be detected by the human eyes. [ ] 3 Which of the following waves will best penetrate fog or low cloud? A infra-red C red light E violet light B radio D ultra-violet [ ] 4 X and Y are different wave motions. In the air, X travels much faster than Y but has a much shorter wavelength. Which types of wave motion could X and Y be? X Y A microwaves red light B radio infra-red C radio sound D sound ultraviolet E ultraviolet radio [ ] 5 The diagram shows different regions of the electromagnetic spectrum. Radio waves Visible light P Gamma Radiation What region does P represent? A microwaves C ultraviolet radiation B sound waves D X-radiation [ ] 6 X-rays, visible light and radio waves are all part of the electromagnetic spectrum. What is the correct order of increasing wavelength? shortest longest A radio waves X-rays visible light B radio waves visible light X-rays C X-rays radio waves visible light D X-rays visible light radio waves [ ]

Hwa Chong Institution Sec 3 (Physics) 3 7 Which of the following statements is true about all electromagnetic waves? A Can be detected by a radio aerial. B Can be detected by photographic film. C Can travel at the same speed in a vacuum. D Can be deflected by magnetic fields. [ ] 8 The wavelength of visible light is approximately A 10-3 km C 10-9 km B 10-6 km D 10-12 km [ ] 9 The wavelength of the blue visible light waves is greater than that of A radio waves C red light waves B X-rays D infra-red waves [ ] 10 The Sun heats the Earth by electromagnetic radiation. Which part of the electromagnetic spectrum is responsible for most of this heating? A Radio waves C Ultraviolet radiation B Infra-red rays D X-ray radiation [ ] 11 Which one of the following can be quickly detected by a person when it is incident on his skin? A Radio waves C Gamma radiation B X-rays D infra-red rays [ ] 12 The diagram below shows the electromagnetic spectrum, with the blue and red ends of the visible light spectrum marked. redblue A B C D Which one of the sections of the spectrum has the following characteristics? “Rays of very penetrating short wavelengths that can be detected on photographic film and they come from the nuclei of atoms.” [ ]

Hwa Chong Institution Sec 3 (Physics) 4 13 A spectrograph is a tool to study spectra. In modern spectrographs, a diffraction grating is often used to “split” the spectrum rather than using a prism. Which of the following statements give the reasons why diffraction gratings are preferred over prisms? 1. A prism does not disperse the colours of the rainbow evenly. Blue and violet portions are spread more than the red part. 2. Because blue and violet wavelengths must pass through a longer distance in the prism’s glass than the red wavelengths, light is absorbed unevenly across the spectrum. 3. Glass prism is relatively opaque to near -UV, which implies that the violet end is much dimmer. 4. A glass prism can shatter easily compared to a diffraction grating. A Statement 1 only. B Statement 1 and 2 only. C Statement 1, 2 and 3 only. D All statements are valid.

Hwa Chong Institution Sec 3 (Physics) 5 14 The microwave oven has a glass window through which we can observe the food while cooking. Is it safe to view through the glass while the microwave oven is in operation? A Yes, it is safe because the window is covered with a metal screen with small holes. B No, it is not safe because if we can see things inside, then both visible light and microwave can leak out of the oven. C Yes, it is safe because there is a chemical coating that prevents the microwave from leaking out of the oven. D Yes, it is safe because glass is opaque to the microwave. 15 Why are infra-red telescope often built on the top of mountains? A So that the telescopes will be closer to the heavenly objects which they are observing. B To reduce the humidity as much as possible. C No one wants bird droppings on their telescope. D So that there are no trees to block their view.

Hwa Chong Institution Sec 3 (Physics) 6 SECTION B SHORT STRUCTURED QUESTIONS 1a) Complete the gaps in the diagram of the electromagnetic spectrum. [2] RADIOWAVES GAMMA b) State two properties of ultra-violet radiation which differ those of infra-red radiation. [2] ________________________________________________________________________ ________________________________________________________________________ c) State two properties which are common to all forms of electromagnetic radiation. [2] ________________________________________________________________________ ________________________________________________________________________ 2 Very short-wavelength radio waves can be used to determine the Moon's distance from the Earth by measuring the time taken for radio waves to travel from the Earth to the Moon and back again. Calculate the delay between the transmission and reception of the signal when the Moon is . 83 9 10 m from the Earth given that the speed of electromagnetic waves is . 83 0 10 ms-1. [2] 3 The figure shows a ray of sunlight incident upon a glass prism such that a spectrum is produced on the screen W. a) Continue the ray to illustrate how the spectrum is formed on the white screen at W. Mark the violet end of the spectrum V and the red end R. [2] sunlight W

Hwa Chong Institution Sec 3 (Phy