Pupil sheet · Communicating with waves
Communicating with waves — final check
Name ______________________ Date ____________
Work alone, with the lesson closed. Answer every question; there are no hints.
1. explain / identify / predict
(a) An engineer on shore steers a robot arm on an oil platform far out at sea, through a satellite link. She must see each move less than 0.1 s after she gives the command. Explain why a link through a geostationary satellite cannot do this, and identify the kind of satellite that can. (b) A designer suggests a satellite that goes round the Earth once a day, but in an orbit that passes over both poles. Predict whether a dish fixed to a roof could point at it all the time, and explain your prediction. (c) Supplement. In a hotel, guests use the wi-fi in a gym in the basement, two floors below the router. Films for up to 300 guests at once come from the town, 20 km away, along a cable under the road. For each, identify the region of the electromagnetic spectrum used, and explain why it suits the job.
(a) Why a geostationary link is too slow, and the right satellites
(b) A once-a-day orbit over the poles
(c) Supplement: the gym’s wi-fi and the cable from the town
2. identify / explain
Supplement. (a) A weather station’s sensor gives a voltage that rises and falls smoothly with every gust of wind. The station sends its readings along an optical fibre as pulses of light, each fully on or fully off. Which row is correct? (b) A village clinic sends the sound of a patient’s heartbeat, picked up by a microphone, as a digital signal to a doctor in a city 300 km away. A pupil says: “The doctor cannot hear a real heartbeat, because a digital signal is only 1s and 0s.” Explain why the pupil is incorrect. (c) The clinic’s cable carries the heartbeat and 29 other calls at the same time. Explain how sending them as digital signals makes this possible.
| Row | The sensor’s voltage | The pulses in the fibre | The pulses are of this kind because |
|---|---|---|---|
| A | analogue | digital | they have only two values, on and off |
| B | digital | analogue | they can take any value in their range |
| C | analogue | digital | they are carried by light, not electricity |
| D | analogue | analogue | the wind they carry varies smoothly |
Circle one answer.
- A
- B
- C
- D
(b) Why the pupil is incorrect, and (c) how 30 calls share the cable