The back of your UVA ID card has a strip of magnetic tape on it. Like a music tape, this strip stores information as a pattern of magnetized patches. The machine that reads this information is essentially a tape player. When someone uses the reader to read your ID card, they pull the card quickly through the reader. It's important that the card move through the reader because the playback head can only respond to moving or changing magnetic fields. That is because moving or changing magnetic fields
A)	produce electric fields that can cause currents to flow in a coil of wire.
B)	produce temperature fluctuations that can easily be detected with a bimetallic strip thermometer.
C)	generate light in photocells; making it possible to detect the pattern of magnetization on the strip.
D)	can change the weight of a small steel ring so that it accelerates up or down.
Answer:A
The back of your UVA ID card has a strip of magnetic tape on it. Like a music tape, this strip stores information as a pattern of magnetized patches. The machine that reads this information is essentially a tape player. When someone uses the reader to read your ID card, they pull the card quickly through the reader. It's important that the card move through the reader because the playback head can only respond to moving or changing magnetic fields. That is because moving or changing magnetic fields
A)	produce electric fields that can cause currents to flow in a coil of wire. B)	produce temperature fluctuations that can easily be detected with a bimetallic strip thermometer. C)	generate light in photocells; making it possible to detect the pattern of magnetization on the strip. D)	can change the weight of a small steel ring so that it accelerates up or down.