A remote changes the television channel only when pointed at it, and stops working when a hand covers its tip. The beam is invisible. Which region of the spectrum does the remote use?

A phone keeps a signal inside a concrete building several kilometers from its mast, with no line of sight to the mast. Which region of the spectrum carries that signal?

A hospital lamp shines invisible radiation onto a work surface. The radiation kills bacteria by damaging their DNA without heating the surface. Which region of the spectrum does the lamp emit?

A firefighter's handheld camera shows a warm person in a smoke-filled room that is completely dark. The camera detects radiation the warm body gives off. Which region does it detect?

A car receives timing signals from satellites orbiting about 20,000 km above Earth to fix its position. The signals pass through cloud and rain. Which region of the spectrum are they?

A machine aims beams from a radioactive cobalt source at a tumor deep inside a patient, using the highest-energy waves on the spectrum. Which region does the machine use?

An internet company sends data as light pulses down a hair-thin glass strand between cities. The pulses are invisible. Which region are they?

A home router broadcasts at 2.4 GHz so laptops in nearby rooms connect. Which region of the spectrum does the router use?

A dark lamp in a museum makes certain minerals glow brightly, and a warning says it can burn unprotected skin. The lamp's own output is barely visible. Which region does it emit?

Grow lamps give plants light with wavelengths from about 400 to 700 nanometers, the range plants use for photosynthesis. Which region of the spectrum is that?

A rotating antenna at an airport sends out pulses that bounce off a metal aircraft 40 km away, through heavy rain, and return to the same antenna. Which region does it use?

A security machine sends radiation through a closed suitcase onto a detector. Dense metal objects inside block far more of it than clothing does, so they show up as dark shapes. Which region does it use?

An FM station reaches listeners in valleys and inside houses, with no clear path from the transmitter to the receiver. Why do radio waves reach these listeners when visible light could not?

A microwave oven is built to emit a frequency that water molecules absorb strongly rather than one that passes straight through food. Why is an absorbed frequency the right choice?

Engineers chose near-infrared light for long-distance optical fiber instead of visible or ultraviolet light. Why does near-infrared suit a glass strand running 80 km between towns?

A radiographer images a broken wrist by sending radiation through the arm onto a detector plate. Why do X-rays produce a useful picture of the bone when visible light cannot?

An MRI scanner images the inside of a patient using strong magnets together with radio waves. Why can it scan the same patient repeatedly with far less concern than an X-ray machine?

A satellite ground station uses microwaves rather than the long radio waves an AM station uses. Why does a link to a satellite need microwaves?

Two families in neighboring apartments each use an infrared remote. Neither remote ever changes the other family's television. Why does infrared suit a remote control for this reason?

A water treatment plant kills bacteria by passing water past ultraviolet lamps instead of infrared lamps. Why does ultraviolet do the job that infrared cannot?

A tumor sits deep inside a patient's abdomen. Doctors treat it with gamma rays rather than ultraviolet light. Why are gamma rays the right choice for a deep tumor?

A router's 5 GHz setting moves data faster than its 2.4 GHz setting, but the connection drops sooner as a laptop moves through the house. Why does the higher frequency behave this way?

A rescue team flies at night above a forest and finds a lost hiker with an infrared camera, even though the ground below is pitch dark. Why does infrared work with no light source?

An air traffic radar keeps tracking planes during a heavy thunderstorm, while the tower's cameras see nothing but cloud. Why do microwaves reach the aircraft when visible light does not?

A television advertisement claims a cell phone's radio signals can break the DNA in nearby cells. State whether this claim is correct.

A dentist drapes a heavy apron lined with lead over a patient's chest before taking an X-ray of one tooth. Why does this apron reduce the patient's risk?

Two pairs of sunglasses are equally dark, but only one is labeled as blocking ultraviolet. An eye doctor recommends the labeled pair. Why does blocking ultraviolet matter?

The window of a microwave oven has a metal sheet with small holes in it. The cook can see the food clearly, but the microwaves stay inside. Why does this screen work?

A hospital stores a gamma source inside thick lead and concrete, but stores an ultraviolet lamp in an ordinary cupboard. Why does the gamma source need such heavy shielding?

During an X-ray, the patient stays in the room but the radiographer steps behind a shielded screen. Why does the operator take a stronger precaution than the patient?

The ozone layer absorbs most of the Sun's shortest ultraviolet before it reaches the ground. What would happen to people at the surface if that ozone thinned over a region?

A welder wears a visor so dark that ordinary sunglasses would not be allowed as a substitute. Which hazard from the welding arc makes that visor necessary?

A town replaces the copper cable carrying its internet with optical fiber. What difference in how the information travels does that change make?

A radio station's broadcast is picked up by every receiver in the town at once, while a fiber link serves only the building its glass strand runs into. State whether that difference is real.

A submarine cruising 100 m below the surface cannot pick up the ordinary radio signals that ships on the surface use. Why?

A digital signal is a stream of on and off pulses, while an analog signal varies smoothly. Why does a digital signal arrive with less noise after passing through many repeaters?

A single optical fiber carries far more phone calls each second than one radio channel can. Which property of the light pulses explains that larger capacity?

A student watching satellite television loses the picture in a heavy storm, while the FM radio in the same room keeps playing. Why does the satellite link fail first?

A laptop connects to a router two rooms away through a closed door, but its infrared port will not talk to a printer in the next room. Why do the two links differ?

A mobile phone call crosses the country mostly through optical fiber. Which part of the journey from the caller's phone is carried by radio waves?