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National 5 Physics Waves & Radiation

National 5 Physics Waves & Radiation. True or False: Can energy be transferred by waves?. Answer TRUE. What is meant by the frequency of a wave?. Answer Frequency is the n umber of waves passing a point per second. What is meant by the period of a wave?. Answer

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National 5 Physics Waves & Radiation

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  1. National 5 Physics Waves & Radiation

  2. True or False: Can energy be transferred by waves? Answer TRUE

  3. What is meant by the frequency of a wave? Answer Frequency is the number of waves passing a point per second.

  4. What is meant by the period of a wave? Answer Period is the time taken for one wave to pass a point.

  5. How does the period relate to the wave’s frequency? Answer Period (T) is the “inverse” of frequency (f). This means … T = 1 / f and f = 1 / T Example 2 waves pass a point each second. So f = 2 Hz and T = 1 / f = 0.5 s In other words, it takes 0.5 seconds for each wave to pass.

  6. What is meant by the wavelength of a wave? Answer The length of 1 wave which is the distance between identical points on 2 waves next to each other. Eg) the distance from one wave crest to the next wave crest.

  7. What is meant by the amplitude of a wave? Answer The height of the wave from the centre line (called the “line of zero disturbance”).

  8. Look at the diagram below. 0.9m 0.4m How many waves are drawn, in total? Answer 6 waves

  9. Look at the diagram below. 0.9m 0.4m Determine the amplitude of these waves. Answer Amplitude is the height from the centre line so, here, amplitude = 0.2m

  10. Look at the diagram below. 0.9m 0.4m Determine the wavelength of these waves. Answer 3 waves in 0.9m … so l = 0.3m

  11. What equation can you use to calculate the frequency of a wave, given the number of waves passing a point in a certain time? Answer f = N / t Where N = number of waves f = frequency in Hertz (Hz) t = time in seconds (s)

  12. What is meant by the speed of a wave? Answer The distance covered by a wave per unit of time. OR “the distance covered per second”.

  13. The speed of waves v = speed in ms-1 t = time in s d = distance in m f = frequency in Hz l = wavelength in m v = f l v = d / t The speed of a wave is simply the distance which the wave crest travels in a certain time (usually 1 second). Also…

  14. Example Waves, of wavelength 50cm, travel the length of a 25m swimming pool. Heather counts 30 of them hitting the end of the pool over a 1 minute period . a) Calculate the frequency of the waves. f = ? N = 30 t = 60s f = N / t = 30 / 60 = 0.5 Hz

  15. v = f l = 0.5 x 0.5 = 0.25 ms-1 1stv = ? f = 0.5 Hz l = 0.5m 2ndv = 0.25 ms-1 d = 25 m t = ? t = d / v = 25 / 0.25 = 100 s b) How long does it take one wave to travel the 25m length of the pool?

  16. What is meant by a transverse wave? Answer A wave where the oscillations happen at right angles to the direction of motion. DIRECTION of WAVE Oscillations are up and down

  17. Give examples of some transverse waves. Answer Any wave from the electromagnetic spectrum... radio, TV, microwaves, infrared, light, ultra violet, x-rays, gamma. and … Water waves DIRECTION of WAVE Oscillations are up and down

  18. What is meant by a longitudinal wave? Answer A wave where the oscillations happen in the direction of motion. DIRECTION of WAVE Oscillations are Forwards and backwards

  19. Give an example of longitudinal waves. Answer Sound waves … (including ultrasound). DIRECTION of WAVE Oscillations are Forwards and backwards

  20. What is meant by diffraction of waves? Answer Waves bending around obstacles.

  21. What wavelengths are better at diffracting; long or short? Answer Long waves diffract better than short waves.

  22. Explain the differences in Radio and TV reception in terms of wave diffraction? Answer Long waves diffract better than short waves. Radio waves have longer wavelengths than TV waves. So, it is easier to pick up radio signals than T.V. signals because radio waves diffract around obstacles better (due to their longer wavelength.)

  23. Sound Signals as Waves on an Oscilloscope What are the missing words below: The pitch of a sound is determined by the __________ of the sound waves. frequency amplitude The volume of a sound is determined by the _________ of the sound waves.

  24. Oscilloscope Patterns for Sound Signals Volume Changes volume increases • amplitude increases • no. of waves stays same Frequency Changes frequency increases • amplitude stays the same • no. of waves increases

  25. Ultrasound Ultrasounds are high frequency sound vibrations beyond the range of human hearing. What is the range of human hearing? 20Hz - 20 000 Hz State one use of ultrasound in medicine To scan and monitor a baby in the womb. Describe how this works Jelly is put on the mum to reduce sound reflections from skin. Ultrasound is transmitted into the womb. The ultrasound reflects from different parts of the baby. The reflected ultrasound travels back to the receiver . The computer uses the different ‘echo times’ from the different parts of the baby to build up an image of the baby.

  26. Noise Levels and Noise Pollution Two examples of noise pollution are: 1. 2. Pneumatic drills Aeroplanes … loud discos, heavy traffic, Kirsten, Heather, Shannon & Lucy  hearing Excessive noise can damage ___________. Sound levels are measured in ____________ Decibels (dB).

  27. Typical Sound Levels Whisper Normal Conversation Danger Level Loud disco 30 dB 60 dB 85 dB 90 dB

  28. State the sections of the ELECTROMAGNETIC SPECTRUM starting with the lowest frequency. Answer radio, TV, microwaves, infrared, light, ultra violet, x-rays, gamma.

  29. State the sections of the ELECTROMAGNETIC SPECTRUM starting with the shortest wavelength. Answer Gamma, x-rays, ultra violet, light, infrared, microwaves, TV, radio.

  30. State the sections of the ELECTROMAGNETIC SPECTRUM starting with the lowest energy. Answer radio, TV, microwaves, infrared, light, ultra violet, x-rays, gamma.

  31. What do all waves in the electromagnetic spectrum have in common. Answer They all travel at the speed of light in air, 3 x 108 ms-1..

  32. The Electromagnetic Spectrum 1. State one application of lasers in medicine. Eye surgery, removing tatoos etc…, 2. State one application of ultra violet. • Treatment of skin disorders (acne), sterilising surgical aparatus,…

  33. 3. State one application of infra red. • Heat treatment for muscles, thermograms (as tumours are warmer than surrounding tissue so they give out more infra red which can be shown on thermograms.) 4. State one application of x-rays. • Detecting broken bones. 5. What is used to detect x-rays? • Photographic film. X-rays blacken the film.

  34. 5. Excessive exposure to ultra violet radiation can be harmful. Why? • It can cause skin cancer. • “Tomography” is the process of taking a series of x-ray slices to build up an image. • A “CT” scan is computerised tomography. • What’s the advantage of this? • A more detailed 3-D image is made so problems can’t be hidden. • Less risk of damage to healthy cells.

  35. Label the following block diagram to show the positions of Bone Photographic film X-ray Machine x-ray machine photographic film bone

  36. For each section of the e.m. spectrum you should be able to state a typical source, detector and application. Here are some suggestions … Radio / TV transmitters Radio / TV receivers Communications Microwave ovens Microwave detection circuit Cooking food / satellite com IR Camera Treat muscle strains Human body Human eye Eye surgery LASER Fluorescent material Treat skin disorders UV lamp Photographic film Detect broken bones X-Ray Machine Gamma camera Treat Cancer Tumours Radioactive substances

  37. What is meant by the term REFRACTION? Answer Light changing speed as it enters a new medium.

  38. Refraction: Air to Glass & Glass to Air air glass normal normal Air to Glass: Light bends towards normal Light slows down to 200 000 000ms-1 Light bends away from the normal Glass to Air: Light speeds up again.

  39. air glass r i Refraction – Labels for Angles normal Label the ‘angle of incidence’, i. This is between the incident light and the normal. Label the ‘angle of refraction’, r. This is between the refracted light and the normal.

  40. Lenses (optional) focus What type of lens is this? Convex How does it affect the light? It brings the rays to a focus. What type of lens is this? Concave How does it affect the light? It spreads the light out. (diverges it)

  41. Describe an Experiment to find the Focal Length of a Convex Lens (optional) 1. Create a sharp image of a distant object on a white screen by moving the lens slowly out from the screen. 2. Measure the distance between the lens and the sharp image on the screen.

  42. Nuclear radiation Radiation can kill living cells (or change them). Describe one medical application of this. Treatment of Cancer Sterilisation of surgical instruments

  43. Radiation is easy to detect. Describe one medical application of this. Tracers…. Radioactive materials are put into the body and the radiation they emit is ‘followed’ around the body by a gamma camera. This is good for locating blockages. The half life of tracers must be carefully chosen. It can’t be too short as the activity might decrease too much during the examination. It can’t be too long as the patient would then be ‘radioactive’ for a time after the examination.

  44. Alpha (a), Beta (b) and Gamma (g) Radiations Radiation can be absorbed by the medium through which it passes. 1. State the range and absorption of alpha, beta and gamma radiations.

  45. 2. Draw a simple model of an atom showing neutrons, protons and electrons. Nucleus consisting of protons (+) and neutrons Tiny electrons (-) in orbit around nucleus 3. What is meant by the term “ionisation”? • Ionisation is when atomslose or gainelectronsto become charged ions.

  46. 4. Which type of nuclear radiation is the most dangerous because it can cause greatest ionisation. (i.e. it can ‘rip’ electrons away from atoms of living things, mutating cells) • Alpha. This is because alpha particles are big and positive so they act like a magnet to the electrons (-) orbiting atoms. 5. Describe how an effect of radiation (on non living things) is used in a detector of radiation. • Film badges in hospitals. These are worn by staff to check exposure levels to radiation. • The radiation ‘fogs’ the film eventually. This is seen when the films are developed.

  47. Activity and Half Life The “activity” of a radioactive source tells us how many radioactive ‘particles’ it emits per second. What is the unit for activity? Becquerels (Bq) What happens to the activity of a radioactive source as time passes? It decreases. What is meant by the term “half life”. “Half life” is the time taken for the activity of a radioactive source to halve.

  48. How do you measure the “half life” of a radioactive source? 1st - Diagram source Geiger Muller Tube computer 2nd – Words of Explanation Set the computer to record the activity of the source at regular time intervals. (eg. each second, minute or hour depending on the question information). Use the data (table or graph) to find out how long it takes for the initial activity of the source to half.

  49. Calculating Half Life Example 1 A source arrives in a hospital with an activity of 1200Bq. After 20 days the activity has dropped to 75 Bq. Calculate the half life of the source. 1200Bq 600Bq 300Bq 150Bq 75Bq 20 days (Each arrow link is 1 half life of time!) 4 half lives = 20 days 1 half life = 5 days

  50. 4 h 4 h 4 h 1800Bq 900Bq 450Bq 3600Bq Example 2 A source has an initial activity of 3600 Bq and a half life of 4 hours. Calculate the activity after 12 hours. 12 h = 3 half life jumps So … final activity = 450 Bq

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