Standard Grade Physics Telecommunications Ink Exercise G1

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Nigel Long
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1 Standard Grade Physics Telecommunications Ink Exercise G1 1. A pupil whistles a note into a microphone connected to an oscilloscope and the pattern observed is shown in the diagram below Without changing the controls on the oscilloscope, a second pupil whistles a louder note of lower frequency into the microphone. Which of the following shows the pattern which would be observed on the screen? (KU1) 2. The diagram shows part of an experimental wave tank used to test model oil rigs. There is a wave generator at one end of the tank. Two depth markers, P and Q, are fixed to the bottom of the tank. (a) (i) Ten waves are made in 5 seconds. Calculate the frequency of the waves. (ii) The distance from the wave generator to the other end of the tank is 12 metres. Eight complete waves are made in this distance. Calculate the wavelength of the waves. (iii) Calculate the speed of the waves.

2 (i) As the waves travel along the tank, the length of depth marker P seen above the water changes from 15 centimetres to 13 centimetres. Calculate the amplitude of the waves at depth marker P. (ii) Why is the amplitude of the waves at depth marker Q smaller than at P? 3. The diagram shows children using a large float in a swimming pool. A wave machine in the swimming pool generates 24 waves per minute on the surface of the pool. (a) Show that the frequency of the wave machine is 0.4 hertz. The wavelength of the waves in the pool is 4.0 metres. Calculate the speed of the waves in the pool. (c)the large float moves up and down on the waves. The vertical distance through which the float rises is 0.5 metres. What is the amplitude of the waves? 4. Two different communication systems are used at a concert. One is for public announcements and the other is used by security staff. (a) Public announcements are made using a microphone and are heard by the audience from loudspeakers. What energy transformation takes place in (i) the microphone (ii) the loudspeakers? Two members of the security staff communicate using two-way radios. Each radio consists of a transmitter and a receiver. (i) At what speed do signals travel between the two-way radios? (KU1) (ii) Explain why no cables are needed to carry the signals between one radio and the other? TOTAL 20

3 Standard Grade Physics Telecommunications Ink Exercise G2 4. Which of the following is the source of energy in a portable radio? A Tuner B Decoder C Amplifier D Battery E Loudspeaker (KU1) 2. The part of a radio which picks up all the signals from the air is called the A modulator B amplifier C tuner D aerial E decoder (KU1) 3. TV signals are sent from Britain to the USA using a satellite link. The device which sends the signals from Britain is called the A modulator B decoder C loudspeaker D amplifier E transmitter (KU1) 4. The period of a satellite orbit depends on A the mass of the satellite B the height of the satellite above the Earth C the average length of an Earth day D whether the satellite orbits above the equator or is in a polar orbit E the rate at which the Earth is spinning (KU1) 3. The frequency range and some uses of different radio wavebands are shown. (a) Give a use, from the table, for a radio wave which has a frequency of 106 megahertz. TV is broadcast in the United Kingdom on the UHF waveband. What is the range of frequencies in this waveband? 4. A reporter from the local radio station is present at the opening of a new factory. The reporter has to get her radio report back to the radio station in time for the next Bulletin. She telephones in her report. (a) Give one advantage of using a telephone in everyday life. A girl, listening to her radio, hears the broadcast of the report of the opening of the factory. The table below shows the frequency range of the different wavebands on her radio receiver. (KU1) Waveband Frequency Range long wave 30 kilohertz 300 kilohertz medium wave 300 kilohertz 3 megahertz high frequency 3 megahertz 30 megahertz F.M. 30 megahertz 300 megahertz (i) The radio station she is listening to has a frequency of 570 kilohertz. State the waveband of this radio station.

4 (ii) Give a possible frequency of a radio station which transmits in the F.M. waveband. (iii) The main parts of a radio receiver are listed below. Aerial Tuner Decoder Amplifier Loudspeaker Electricity supply Which part is used to select a particular radio station? (KU1) 6. A caller makes a telephone call using a mobile phone. The call is received at a telephone in a house. The message from the caller reaches the person receiving the call in four stages. Stage 1 The caller speaks into the mobile phone Stage 2 The mobile phone transmits a signal to an aerial at a receiving station Stage 3 The signal is transmitted along an optical fibre to an exchange Stage 4 The exchange is connected by a wire link to a telephone in the house. (a)(i) Use the words from the list below to state how the message is transmitted at each of the above stages. electrical light microwave sound (stages1-3 PS3) (stage 4 KU1) (ii) During which stage (1 4) does the message travel most slowly? Copy and complete the diagram below to show the effect of the curved reflector at the receiving station. (c) A section of the optical fibre used in Stage 3 is shown below. Copy and complete the diagram to show how the signal is transmitted along the optical fibre. TOTAL 19

5 Standard Grade Physics Telecommunications Ink Exercise C1 5. At a local swimming gala, the swimmers start when they hear the sound of the starting horn. This horn also sends an electronic signal to start timing the race. At the start of the race, the swimmer in lane 1 is a distance of 2m from the horn and the swimmer in lane 8 is a distance of 19m from the horn. (a) The swimer in lane 1 hears the sound of the horn first. Calculate how much later the swimmer in lane 8 hears the sound. (PS3) As each swimmer finishes the race, an electronic touch sensor detects the swimmer s arrival at the finishing point. After the race, the scoreboard gives the following information. (i) Using your answer to part (a), or otherwise, explain why the swimmer in lane 8 should be awarded first place. (ii) Suggest an improvement to the starting, or timing, system that would reduce the unfairness of the timing.

6 6. The depth of the seabed is measured using pulses of ultrasound waves. The ultrasound waves are transmitted from a stationary ship. The waves are reflected from the seabed as shown and are detected by equipment on the ship. The transmitted ultrasound waves have a frequency of 30 khz and travel at a speed of 1500 m/s in water. (a) One pulse of ultrasound waves is received back at the ship 0.2s after being sent out. (i) Calculate the depth of the seabed. (KU3) (ii) Calculate the wavelength of the ultrasound waves in the water. The ultrasound waves lose energy as they travel through the water. The transmitted wave is displayed on an oscilloscope screen as shown below. Copy and complete the bottom part of the diagram to show the trace produced by the reflected wave. (c) The frequency of the transmitted wave is increased to 60 khz. What happens to the time interval between the transmitted pulse and the reflected pulse. TOTAL 15

7 Standard Grade Physics Telecommunications Ink Exercise C2 7. The tuning dial on a radio displays three different bands which are labelled frequency modulation (FM), medium wave (MW) and long wave (LW). The frequency range for each band is shown below. (a) The radio receives a signal with a wavelength of 1190m. To which of the above bands is the radio tuned? You must show clearly the calculation used to reach your conclusion. Signals cannot be received from one of the bands when this radio is used in a village which lies in a deep valley surrounded by hills. (KU3) (i) Explain which band is not received. (ii) Houses in the village are unable to receive programmes from the local TV station but can receive satellite TV programmes broadcast on similar frequencies. Suggest an explanation for this. 2. (a) At a science exhibition, a display has two videophones connected together. A videophone is a special telephone, which can be used to send both video signals (for pictures) and audio signals (for sound) along a telephone link. (i) A video signal used to test the link produces the black and white pattern shown. Describe how a black and white pattern is built up on the screen.

8 (ii) It is only possible to send 3 complete pictures every second along the link to the receiving videophone. Explain why a person s movement as seen on the videophone, appears jerky. Another display has been set up to show how different colours can be seen on a TV screen. Switches R, G and B on a panel control each of the electron guns in the TV. Each switch turns a gun off when pressed. The colour controlled by each switch is shown in the table below. What colour is the screen when the display is on and (i) no switches are pressed; (ii) only switches B and G are pressed; (iii) only switch B is pressed? (PS3) 3. In 1996 the Olympic Games were held in the city of Atlanta in the USA. (a) TV pictures of the Games were transmitted from the USA to Britain. The TV signals were carried by microwaves. The microwaves travelled from the USA to Britain via a geostationary satellite positioned km above the surface of the Earth as shown in the diagram below. (i) What is meant by saying that the satellite is geostationary? (ii) The frequency of the microwaves used was 12 GHz. Calculate the wavelength of the microwaves used in the transmission. Newspaper reporters at the games were able to fax their reports back to Britain by a telephone link. The telephone link used an 8000 km length of glass optical fibre. (Speed of light in glass = 2.0 x 10 8 m/s) How long did it take the telephone signals to travel from the USA to Britain? TOTAL 20

Speed of Sound. 2. How long will it take sound to travel a distance of 200 m?

Speed of Sound. 2. How long will it take sound to travel a distance of 200 m? Speed of Sound Remember : speed = distance v = d time t Data : Speed of sound in air = 340m/s 1. How far will sound travel in 5 seconds? 2. How long will it take sound to travel a distance of 200 m? 3.