Questions: Using Waves to Send Information: Analog and Digital Signals

Question 1

Which of these is a digital signal?

• A. The smooth groove on a vinyl record
• B. A flashlight blinking short and long flashes in Morse code
• C. The changing height of a water wave
• D. The sound of a person humming

Answer: (B)

Morse code uses only two kinds of flashes (short and long) with gaps between them. Each part of the message is one of a few set values, which is what makes a signal digital.

Question 2

A radio station sends sound waves through the air all the way to your radio.

• T. True
• F. False

Answer: False

Sound waves fade quickly and travel slowly. The station sends radio waves, which are invisible light. Your radio picks up the pattern in the radio waves and uses it to make sound.

Question 3

Why can a digital music file be copied many times without losing quality?

• A. Digital files are made of sound waves
• B. Each copy only has to tell a 1 from a 0, so small errors can be fixed and the copy matches the original
• C. Digital copies are bigger than the original
• D. Computers add extra music to each copy

Answer: (B)

A receiver only needs to decide whether each piece is a 1 or a 0. A little noise does not change that decision, so each copy can be exact.

Question 4

Design a simple light code to send the answers 'yes' and 'no' across a dark field. Explain why your code would still work if the light flickers a little.

Model answer: Example: one long flash means yes, two short flashes mean no. A small flicker does not change the number or length of flashes much, so the receiver can still tell which message was sent.

A good code uses patterns that are very different from each other. Then small disturbances, called noise, do not turn one message into the other.