lecture25a - ConcepTest 22.2 ConcepTest The electric field...

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Unformatted text preview: ConcepTest 22.2 ConcepTest The electric field in an EM wave traveling northeast oscillates up and down. In what plane does the magnetic field oscillate? Oscillations Oscillations 1) In the north-south plane. In 2) In the up-down plane. In 3) In the NE-SW plane. In 4) In the NW-SE plane. 5) In the east-west plane. ConcepTest 22.2 ConcepTest The electric field in an EM wave traveling northeast oscillates up and down. In what plane does the magnetic field oscillate? Oscillations Oscillations 1) In the north-south plane. In 2) In the up-down plane. In 3) In the NE-SW plane. In 4) In the NW-SE plane. 5) In the east-west plane. The magnetic field oscillates perpendicular to BOTH the electric field and the direction of the wave. Therefore the magnetic field must oscillate in the NW-SE plane. ConcepTest 22.3 ConcepTest Before the days of cable, televisions often had two antennae on them, one straight, and one circular. Which antenna picked up the magnetic oscillations? TV Antennas 1) the circular one the 2) the straight one the 3) both equally, they were straight and circular for different reasons. reasons. ConcepTest 22.3 Before the days of cable, televisions often had two antennae on them, one straight, and one circular. Which antenna picked up the magnetic oscillations? The varying B field in the loop means the flux is changing and therefore an EMF is induced. TV Antennas 1) the circular one the 2) the straight one the 3) both equally, they were straight and circular for different reasons. reasons. ConcepTest 22.4 ConcepTest If a radio transmitter has a vertical If antenna, should a receiver’s antenna be vertical or horizontal vertical horizontal to obtain the best reception? Radio Antennas 1) vertical vertical 2) horizontal horizontal 3) doesn’t matter doesn’t ConcepTest 22.4 If a radio transmitter has a vertical If antenna, should a receiver’s antenna be vertical or horizontal vertical horizontal to obtain the best reception? Radio Antennas 1) vertical vertical 2) horizontal horizontal 3) doesn’t matter doesn’t If a wave is sent out from a vertical antenna, the electric field oscillates antenna up and down. Thus, the receiver’s up E field of wave antenna should also be vertical so antenna vertical that the arriving electric field can set the charges in motion. E field of wave ConcepTest 22.5 ConcepTest Heat Insulation Imagine you are an alien from another planet with infrared eyes. Imagine infrared What do you see when you look around the room? What 1) Bright spots where the bodies are and dark elsewhere. 1) 2) Dark spots where the bodies are and bright elsewhere. 3) The same as what we see, only everything looks red. 4) The same as what we see, except that red is invisible. ConcepTest 22.5 Heat Insulation Imagine you are an alien from another planet with infrared eyes. Imagine infrared What do you see when you look around the room? What 1) Bright spots where the bodies are and dark elsewhere. 1) 2) Dark spots where the bodies are and bright elsewhere. 3) The same as what we see, only everything looks red. 4) The same as what we see, except that red is invisible. Bodies are sources of heat and therefore emit infrared radiation. emit An alien with an instrument to detect infrared would see these sources as bright spots. sources Infrared photo of a building to check the heat insulation – where are the problem spots in this case? ConcepTest 22.6 ConcepTest Since Superman is from the planet Since Krypton his eyes are sensitive to the entire electromagnetic spectrum. Does that mean he can use x-ray vision to see that Lois Lane is being kidnapped in the other room? kidnapped Superman 1) Yes, no problem 2) Nope, he can’t 2) 3) Need more information 3) ConcepTest 22.6 Since Superman is from the planet Since Krypton his eyes are sensitive to the entire electromagnetic spectrum. Does that mean he can use x-ray vision to see that Lois Lane is being Superman 1) Yes, no problem 2) Nope, he can’t 2) 3) Need more information 3) kidnapped in the other room? kidnapped X-ray vision means that Superman’s eyes can receive x-rays, but not send them! receive send So what would have to happen for him to see Lois Lane being kidnapped? ...
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