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Physics

National 4/5

Anderson High School

Waves and RadiationElectromagnetic SpectrumExtra Question Booklet

Nat

Radio and Television Two equations which are useful in answering questions on waves are

Where v = average speed in metres per second (m/s)f = frequency in hertz (Hz) = wavelength in metres (m)d = distance in metres (m)t = time in seconds (s)

Helpful Hint Radio and television waves are electromagnetic waves

whichtravel at a speed of 3 x 10 8 m/s (3 00 000 000 m/s) through space.

Two more useful units are:

1 kHz = 1 000 Hz = 1 x 103 Hz1 MHz = 1 000 000 Hz= 1 x 106 Hz

1. A radio wave has a wavelength of 9 540 m. What is the frequency of this wave?

2. Calculate the frequency of a radio wave which has a wavelength of 442 m.

3. A radio wave with a frequency of 6 500 Hz would be called a very low frequency radio wave (VLF). What is the wavelength of this radio wave?

4. The navy use long wavelength radio waves for telecommunication.

Calculate the frequency of a radio wave with a wavelength of 8600 m used by the navy to communicate at sea.

5. Different radio stations use different frequencies of radio wave to carry information from the radio transmitter to the radio receiver. Radio frequencies used for sound broadcasting are often measured in kilohertz (kHz) or megahertz (MHz).

Convert each of the following frequencies into hertz.(a) 1 215 kHz (d) 88 MHz

© GMV Science. Photocopiable only by the purchasing institution. 2

v=f v d t

=and

Radio and Television (b) 810 kHz (e) 97·6 MHz(c) 548 kHz (f) 850 MHz.

6. If you look in a newspaper or television magazine you will see information on radio and TV programmes. The radio section

usually gives you the frequency of each radio station so that you can find the programme that you want to listen to on the radio.

Below is a list of some radio stations you can tune into on medium wave (MW).

(a) Virgin Radio MW 1 215 kHz(b) Radio Scotland MW 810 kHz(c) Radio Forth MW 1 548 kHz

Calculate the wavelength of each of these stations in metres.

7. Many BBC radio programmes are broadcast on FM. FM broadcasts provide good sound quality and suffer less interference than MW broadcasts. FM broadcasts use very high frequency waves which are measured in Megahertz (MHz)

Look at the list of frequencies for BBC broadcasts on FM.

Radio 1 FM 97·6 MHzRadio 2 FM 88 MHzRadio 3 FM 92·4 MHzRadio 4 FM 96·1 MHz

Calculate the wavelength of each of these radio waves in metres.

8. Radio 5 Live broadcasts a news programme called ‘News Extra’ at 7.00 pm on MW 433 m.

Calculate the frequency of this broadcast9. Radio Scotland broadcasts programmes on both FM and MW.

Between 9pm and 10 pm a classical music programme called ‘The Score’ is broadcast on FM (3·2 m ) only. At the same time on MW (370·3 m) Gaelic programmes are broadcast.

(a) Calculate the frequency of the programme called ‘The Score’.

(b) What frequency would you tune your radio to in order to receive the MW programmes?

10. A television signal is sent in the same way as a radio signal. To broadcast a television programme two radio carrier waves


Radio and Television are needed. One wave carries the picture information and one wave carries the sound information.BBC 1 use a 621·25 MHz radio wave to carry the sound signal and a 615·25 MHz radio wave to carry the picture signal.

Calculate the wavelength of each of these carrier waves.

11. An Olympic athlete can run 100 m in 10 seconds. How far would a radio wave travel in 10 seconds?

12. How long would it take for a radio signal to travel from the broadcasting station to a radio receiver 40 km away?

13. How far could a radio wave travel in 3 minutes?

14. A long distance lorry driver uses a CB radio to talk to a colleague 48 km away. How long does it take for the radio wave to travel this distance?

15. On 12 December 1901 Gugliemo Marconi sent the first radio message across the Atlantic ocean. The message travelled a total distance of 3 440 km between Cornwall in England and Newfoundland in Canada.How long did it take the radio message to travel between

England and Canada?16. Air traffic control sends a radio message to an aeroplane that

is preparing to land at Aberdeen airport. The plane is instructed to descend to 1000 m.The plane was 8 km from the control tower when it received

the instruction.

Calculate how long it took for the radio message to reach the aeroplane.


8 kmcontrol tower

Radio and Television

17. A police patrol car is called to the scene of a road traffic accident. The police constables received the message sent from their police station on the car radio. The message took 6·5 x10-5 seconds to reach the car. Calculate how far the patrol car is from the station when it receives the message.

18. A Channel 4 programme is transmitted from an aerial outside Inverness. A radio wave of frequency 645·25 MHz carries the sound signal. The picture signal is carried by a radio wave of frequency 639·25 MHz.

(a) Calculate the wavelength of the radio wave carrying the picture signal.

(b) How long would it take for the sound signal to reach Aberdeen which is 152 km from the transmitter?

(c) How far would the picture signal travel in 8·5 x 10 -4 seconds?

19. Radio waves of different frequencies have different properties and are used for different purposes.Radio waves of frequency 30 Hz - 3 kHz are called extra low frequency (ELF) and are used for communicating with submarines which are moving in deep water.

(a) What is the wavelength of a 30 Hz ELF wave in air?

(b) A navy ship sends a radio message of frequency 3 kHz to a submarine directly below it .The signal travels at 2 x 108 m/s in water. If the signal takes 3·4 x 10-7 seconds to reach the submarine calculate the depth, d, at which the submarine is cruising.


d

Radio and Television 20. Frequencies of 3 - 30 kHz are called very low frequency (VLF)

and are used by the army for telecommunications.

(a) A 16 kHz signal is used by the radio operator at Field Headquarters to send a message to an army patrol during a field exercise. Calculate the wavelength of this signal.

(b) How long will it take this message to reach the patrol which is 9 km away from Field Headquarters?

(c) An hour later the patrol sends a radio message to Field Headquarters giving their new position. The message takes 1·3 x 10-5 seconds to reach HQ. How far is the patrol from headquarters now?


Electromagnetic Spectrum 1In this section the two equations which you will find most useful are

Where v = average speed in metres per second (m/s) f = frequency in hertz (Hz) = wavelength in metres (m) d = distance in metres (m) t = time in seconds (s).

Helpful HintAll Electromagnetic waves travel at a speed of 3 x108 m/s ( 300 000 000 m/s ) through space.A useful unit of distance is the nanometre

1 nm = 0·000 000 001 m = 1 x 10-9 m

1. Electromagnetic waves with frequencies close to the frequency of visible light have very short wavelengths often measured in nanometres (nm).

Convert the following wavelengths into metres:

(a) 5 nm(b) 400 nm (c) 700 nm (d) 1 500 nm.

2. Our eyes can detect visible light with wavelengths ranging from 400 nm to 700 nm. Light with a wavelength of around 400 nm is violet in colour. Red light has a wavelength of around 700 nm.

Calculate the frequencies of violet light and red light.

3. A doctor examines a patients stomach using a fibrescope. White light is shone down a bundle of optical fibres called the light guide and reaches the end of the fibrescope in 1·75 x10-9 seconds. If the light guide is 35 cm long calculate the speed of the light as it travels down the fibres.

4. Peter sprained his ankle playing f football. The physiotherapist uses in fra infra-red radiation of wavelength 1·2 x 10 -4 metres to heat the tissue in his ankle and help it heal. Calculate


v = d t

v = f

Electromagnetic Spectrum 1 the frequency of this radiation.5. An elderly patient is suffering from pains in his knees. The doctor in the hospital takes a ‘heat picture’ called a thermogram of

the knees and detects an inflammation of the joints caused by arthritis. The infra red radiation being given out by the knees is of frequency 5 x 1012 Hz. Calculate the wavelength of this radiation.

6. The ancient Egyptians used ultraviolet radiation from the sun’s rays to treat the skin complaint acne. Ultraviolet light is still used today in hospital to treat acne. Calculate the wavelength of UV light of frequency 8·8 x1016 Hz

7. Microwaves are part of the electromagnetic spectrum and have many uses from telecommunications to cooking. Microwaves of wavelength 12 cm are used in ovens to cook food. The human body gives out microwaves of wavelength 9 cm which can be detected by a small aerial placed in contact with the skin. These microwaves allow doctors to measure the temperature of organs inside the body.Calculate the frequency of microwaves emitted from the body.

8. An argon laser which produces blue/green light of wavelength 500 nm is being used to treat Mrs Doig who suffers from diabetes. The laser is used to seal blood vessels which have been bleeding into the eye and damaging her sight. Calculate the frequency of the light produced by the laser.

9. A low power red argon laser (700 nm) is directed through an optical fibre to a cancerous tumour in a patients throat. The laser light activates a drug injected into the patient which will kill the cancerous cells.

(a) What is the frequency of the red light produced by the laser?(b) Calculate how long it will take for the light to travel 95 cm

down the optical fibre if it travels at a speed of 2·2 x 108 m/s.10. X - rays were discovered in 1895 by Wilhelm Rontgen. X - rays

are now widely used in medicine and dentistry.


Electromagnetic Spectrum 1

John is having an X-ray taken of one of his molars which is giving him pain. The dentist sets up the X-ray apparatus and goes to stand behind a lead screen. The X - rays used have a frequency of 2 x1017 Hz.

(a) Calculate the wavelength of these X-rays.

(b) How long will it take for these X -rays to travel 10 cm from the X- ray machine to John’s tooth?


Electromagnetic Spectrum 21. Describe a use in medicine for each of the following:

(a) the laser(b) X-rays(c) ultraviolet radiation.

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2. Read the passage below and use it to answer the questions that follow.

The sun is a star 150 x106 km from Earth which produces enormous amounts of energy in the form of electromagnetic waves. We can detect the visible light from the sun with our eyes but we cannot detect the invisible ultraviolet light which also reaches Earth. Exposure to the ultraviolet light from the sun can produce a change in the colouring of the skin which we call a sun tan.

There are three types of ultraviolet radiation. We are constantly exposed to UVA and we need this for healthy growth and to make vitamin D in our bodies. UVA light has wavelengths in the range 315 to 400 nm. UVB light has wavelengths in the range 280 to 315 nm. Most of the UVB light from the sun is removed by the layer of ozone in the atmosphere around the Earth. Scientists have found that there is a hole in the ozone layer which is allowing more UVB to reach us on the surface of the earth. UVB can cause a skin cancer called melanoma. The third type of UV light, with wavelengths in the range 200 to 280 nm, is called UVC .

People who are going to be exposed to the sun for any length of time should protect their skin with sun tan cream. An extract from the back of a bottle of sun tan cream is given on the next page..

Bronzage cream protects the skin from sun burn, premature skin ageing and long term


Electromagnetic Spectrum 2damage to the internal structure of the skin by filtering out the harmful UVA/UVB rays from sunlight.

Bronzage is water resistant even after a swim of 30 minutes.

(a) Calculate how long it takes for ultraviolet light to travel from the sun to Earth.

(b) Construct a table giving the wavelengths of UVA, UVB and UVC light.

(c) Calculate the frequency of the shortest wavelength UVC light.

(d) What type of UV light has a frequency of 7·5 x 1014 Hz?

(e) What range of wavelengths does Bronzage sun tan cream block?


Electromagnetic Spectrum 3 1 a) List the members of the electromagnetic spectrum in order

with the largest wavelength first.b) What do all the members have in common?

2. How far will radio waves travel ina) 2 m s b) 0.25 m sc) 1 m s.

3.. Calculate the wavelength of waves of frequency a) 5 GHz b) 4 MHz c) 200 GHz.

4. Calculate the transmission frequency of Radio Scotland broadcasting on 370 m on the Medium waveband. Give your answer in MHz.

Waves and Optics (Int 2) – Student Material 12

Electromagnetic Spectrum 41. Describe one use for optic fibres in medicine and explain why

using optic fibres in medicine are an advantage when compared with other forms of internal examination.

2. The Electromagnetic spectrum is made up of a variety of partsa. Copy and complete the EM spectrumb. Identify a suitable detector for each type of radiation and fill

in the lower row of the table

_______ Wavelength Short ____________

TV & Radio waves

Infraredrays

UV Gammarays

Low _______ ______ Frequency

1.2.

3. Visible light is the part of the EM spectrum that we can see. This light is seen as white light but it is made up of 7 different colours. Name the seven colours which make up white light.

4. In industry there are various uses for parts of the EM spectrum. One such use is to use a type of radiation to detect cracks in metal pipes which cannot be seen with the human eye.

a. Name the type of radiation that could be used to detect the cracks.

b. What safety precautions would you need to take when using this radiation?

c. Give another use for this type of radiation.

5. Using the following frequencies and wavelengths for parts of the EM spectrum calculate the speed of the waves using the formula v=fxλ

Name Wavelength FrequencyRadio wave 3.12m 96.2x106Hz

Visible Red light 750nm(750x10-9m) 4x1014HzX Ray 1nm (1x10-9m) 3x1017HZ

What can you say about the speed of the all waves in the EM spectrum?

SIC Physics Development Group MB 13

Electromagnetic Spectrum 51. Thermal imaging cameras detect infrared radiation.

Give 2 examples of how they or infrared radiation are used:-a. by the emergency services.b. by doctors and physiotherapists.c. in industry and leisure.

2. Ultraviolet light is sometimes referred to as ‘black light’ and isboth essential for the human body and potentially harmful and it can kill bacteria.

a. What are the dangers of ultraviolet light and why does our body need it?

b. Give 2 examples of how it is used either (i) by medical practitioners. OR(ii) in recreation industry – including sports centres

and night clubs. OR(iii) in forensics.

3. Make a list the radiations of the electromagnetic spectrum in order of increasing wavelength.a. Add an arrow to your list showing the direction of

increasing frequency.b. Name a detector for each type of radiation.

4. What do all the radiations of the electromagnetic spectrum have in common?

5. In Summer 2012 the Olympic and Paralympic games were held in London. TV pictures of the events were transmitted to the USA. Microwaves carried these signals to a geostationary satellite 36000km above the Earth’s surface.

a. Given that the microwaves had a frequency of 12 GHz calculate their wavelength.

b. How long did it take the microwaves to reach the satellite?

6. An infrared wave is used to detect people buried after an earthquake. It has a wavelength of 2.4 x 10-5m.

a. Calculate the frequency of the wave.b. The waves are reflected back by a buried casualty.

How far below the rubble is the casualty?

7. X-rays have been used for many years by dentists, doctors and radiographers. More recently their usage has expanded and the are now used in industry and museums.

a. Explain how an X-ray photograph is taken and explain why exposure to X-rays should be minimised and what safety precautions should be taken.

SIC Physics Development Group JM 14

Electromagnetic Spectrum 5b. State how they effect photograph film and how this can

be used in:(i) Medical diagnosis by dentists or doctors.(ii) Industry to check welds and aircraft

superstructure.

8. X-ray technology has advanced greatly since Roentgen took the first X-ray in 1895. CT or CAT scanners are now routinely used in hospitals, X-ray scanners are used in airports and in radiotherapy.

a. What do CT scanners do and what advantages does this have over a traditional X-ray photograph?

b. What are they used for in museums and airports and why is this useful?

c. What is X-ray therapy and what safety precautions must be taken?

9. Gamma rays are the most energetic of the electromagnetic spectrum and can pass straight through the body. They kill bacteria and damage healthy tissue.

a. How are they used in the medical industry for:i. In diagnosis? e.g. radioactive tracers, PET scans.ii. In treatment? e.g. radiotherapy.

b. How are they used in the food industry and what other industrial uses are there?

SIC Physics Development Group JM 15

Numerical AnswersRadio & Television P 2 - 61. 31 447 Hz2. 678 733 Hz3. 46 154 m4. 34 884 Hz5.(a) 1.215 x106 Hz(b) 8.10 x 105 Hz(c) 5.48 x 105 Hz(d) 8.8 x 107 Hz(e) 9.76 x 107 Hz(f) 8.50 x 108 Hz6.(a) 246.91 m(b) 370.37 m(c) 193.80 m

7.Radio 1-3.07 m Radio 2-3.41m Radio 3-3.25 m Radio 4-3.12 m8. 6.93 x 105 Hz9.(a) 9.38 x 107 Hz(b) 8.1 x 105 Hz10.picture wave0.4msound wave0.48m11. 3 x 109 m12. 1.33 x 10-4 s13. 5.4 x 1010 m14. 1.6 x 10-4 s

15. 0.01 s16. 2.67 x 10-5 s17. 19 500 m18.(a) 0.47 m(b) 5.1 x 10-4 s(c) 255 000 m19.(a) 1 x 107 m(b) 68 m20.(a) 18750 m(b) 3 x 10-5 s(c) 3 900 m

Electromagnetic Spectrum 1 P 7 - 91. (a) 5 x 10-9 m (b) 4 x 10-7 m (c) 7 x 10-7 m (d) 1.5 x 10-6 m2.violet-7.5 x1014 Hz red -4.3 x1014 Hz3. 2 x 108 m/s4. 2.5 x 1012 Hz

5. 6 x 10-5 m6. 3.41 x 10-9 m7. 3.33 x 109 Hz8. 6 x 1014 Hz9. (a) 4.27 x 1014 Hz (b) 4.32 x 10-9 s10. (a) 1.5 x 10-9 m (b) 3.33 x 10-10 s

Electromagnetic Spectrum 2 P 10 - 111. (a) Laser – bloodless scalpel, removing birthmarks and tattoos,

treating cancer, early diagnosis of illness (experimental) (b) X-rays – used to detect broken bones, used to create 3-D images in CAT scans, used to kill cancerous cells in radiotherapy (c) Ultraviolet radiation – used to sterilize equipment, kill bacteria and viruses in the air and water used in operating rooms, treat skin conditions such as psoriasis and vitiligo.

2. (a) 500 s(b)

(c) 15 x 1015 Hz(d) UVA(e) 280 nm - 400 nm

GMV Science. Photocopiable only by the purchasing institution.Waves and Optics (Int 2) – Student MaterialSIC Development group PB 16

Radiation Wavelength (nm)UVA 315 – 400UVB 280 – 315UVC 200 - 280

Numerical AnswersElectromagnetic Spectrum 3 P 121. a) Radio and TV, Microwaves, Infra red, Visible light,

Ultraviolet, X-rays, Gamma raysb) All travel at the speed of light (3 x 108m/s)

2. a) 600,000mb) 75,000mc) 300,000m

3. a) 0.06mb) 75 mc) 0.0015m

4. 0.81MHz

Electromagnetic Spectrum 4 P 13 1 Optical fibres can be used in an endoscope. This is used to see inside a patient. Lungs, stomach and the intestines can be investigated without surgery. If it is used to inspect other internal organs the incision used to allow the endoscope access is much smaller meaning the patient has a shorter stay in hospital and less to recover from.2 Radio and TV, Microwaves, Infra red, Visible light, Ultraviolet, X-

rays, Gamma raysRadio and tv/microwave – tuned circuit and aerial, Infrared – photodiode, visible light – eye, ultraviolet – fluorescent materials, x rays and gamma rays – photographic film.3 Red, Orange, yellow, green, blue, indigo, violet. (ROY-G-BIV)4. a) x-rays can be used to detect cracks in welds and pipes.

b) Avoid exposure to x-rays by screening and limiting the time working with them.c) Screening luggage at airports for security

5. Radio wave – 300144000m/svisible red light – 300000000 m/sx-ray – 300000000 m/sEverything in the electromagnetic spectrum travels at the speed of

light (3 x 108m/s)


Numerical AnswersElectromagnetic Spectrum 5 P 14 -15 1(a) Firefighters use thermal imaging cameras to find casualties in

smoke filled rooms and to identify hotspots or the seat of a fire. They can also be used to find casualties trapped under collapsed

buildings. (b) Thermograms are used by doctors to diagnose illness – different body temperatures appear as different colours. If you are unwell the body would not be at the expected temperature.

Physiotherapists use infrared lamps to heal damaged muscle tissue – this speeds up the process.

(c) Thermal imaging cameras are used to check buildings for heat loss and identify where additional insulation is required. They can also be used to check for overheating in electrical circuitry and equipment. They are used in the remote controls of TVs and other electronic equipment.

2(a) The body needs ultraviolet radiation to manufacture vitamin D. Excessive exposure can case sunburn and skin cancer.

b(i) It can be used to help treat skin conditions such as eczema, psoriasis and acne. Dentists use it to seal teeth and set fillings. They are also used to sterilise equipment b(ii) The are used in tanning studios, to sterilise the air in air conditioning systems and to kill the bacteria in swimming pool water. They are used in night clubs and discos to make cloths ‘glow’ – UV causes some of the chemicals in the clothing materials or the ‘post wash’ residues to fluoresce. b(iii) No hiding from UV blacklight which plays a vital role from scene of crime to post mortem.Ultraviolet lights (blacklights) are extensively used for screening techniques during forensic investigations at crime scenes and in the laboratory. It is the first choice when examining biologically contaminated evidence because UV analysis is non-destructive. It permits precise images and preliminary identification of evidence prior to other analytical techniques, i.e. luminol.Applications range from searching for blood traces, other bodily fluids, finger prints and foot prints to the revelation of subcutaneous bruising on the body, including post mortem which may not be visible under other lighting conditions. Bodily fluids such as saliva, semen, vaginal fluids, urine and perspiration will fluoresce under UV blacklight. This makes UV fluorescent inspection the ideal solution for detecting this type of trace evidence at crime scenes or on evidence collected as a scene, e.g. clothing, bed linen, towels and other objects.UV blacklight inspection will also detect some drugs, for example LSD.

3(a) TV& Radio, Microwaves, Infrared, Visible light, Ultraviolet, X-rays, Gamma rays.

(b) Gamma rays, X-rays, Ultraviolet, Visible light, Infrared, Microwaves, TV&radio.


Numerical Answers4. They all travel at 300 000 000m/s the speed of light.5 (a) 0.025m (b) 0.12s6 (a) 1.25 x 1013Hz(b) 1.8m7. Gamma Rays – Geiger Muller tube, photographic film, gamma

camera, scintillation counter.X-rays – Photographic film.

Ultraviolet light – Fluorescent paint, photodiodes.Visible light - Photographic film.Infrared – Blackened thermometer.Microwaves – Diode probe.TV & Radio – Aerial.8(a) Photographic film is placed underneath the patient, the X-ray

machine is placed above the patient and X-rays are fired at them. X-rays will pass through the body and be detected by the photographic film. X-rays are absorbed by bone and tissue, the blacker the film the greater the number of X-rays reaching it. So a

healthy bone will appear white and a broken bone will have a dark line where there is break.

X-rays will damage healthy tissue so exposure to X-rays must be minimised. Sometimes lead blankets are placed over the parts of the body not being examined to prevent unnecessary exposure. Radiographers and dentists will leave the room while an X-ray is being taken and may observe through leaded glass windows.

b(i) Dentists can check for tooth decay – this appears as a dark shadow in apparently healthy teeth, for undescended teeth and fillings. Doctors can check for broken bones, scarring on the lungs – common when patients have or have had tuberculosis and for certain cancers – the

denser cancerous growths absorb more X-rays than healthy tissue or foreign bodies inside the body.b(ii) Metals will absorb X-rays so cracks in welds or superstructure will appear in the same way as broken bones do


Numerical Answers

9(a) CT scanners cut the body up into thousands of X-ray slices. The information is passed to a computer which can put the slices together to produce a 3-D picture. Unnecessary information can be removed and exact pictures of tumours and broken bones can be produced. This allows exact doses of X-rays and other treatments to be calculated, surgical routes and the restructuring of bones to be planned.

(b) They can show what is inside mummies, to check foe crack and damage in artefacts etc without having to take them apart and causing further damage.

They can show what is inside luggage, what undergarments a person is wearing, what is in their pockets... This means that any suspect items can be removed and investigated in more detail.

(c) This is quite simply using high energy X-rays to kill tumours. The X-rays are fired from a rotating ‘gun’ and are focussed on the tumour. As the machine rotates around the body the exposure to healthy tissue is

minimised. 10a(i) Radioactive chemicals are dissolved or placed in a liquid that is tied

to particular hormones. These are either injected into the body or swallowed and a gamma camera will detect the gamma rays as they pass through the body and their route can be plotted. The chemicals will concentrate in a particular organ and this can give information regarding blood flow, blockages and the presence of particular tumours.

a(ii) This is quite simply using gamma rays to kill tumours. The gamma rays are fired from a rotating ‘gun’ and are focussed on the tumour. As the machine rotates around the body the exposure to healthy tissue is

minimised.(b) They are used to kill the bacteria that causes foods to rot – this extends shelf life and to delay or prevent the germination of some grains.

They are used to sterilise surgical instruments and other equipment, to check the thickness of paper and other materials and to examine shipping crates both before leaving and after arrival at ports.


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