Sound that is perceptible by humans has frequencies from about 20 Hz to 20,000 Hz. In air at standard temperature and pressure, the corresponding wavelengths of sound waves range from 17 m to 17 mm. Sometimes speed and direction are combined as a velocity vector; wave number and direction are combined as a wave vector.
Price of a Stamp. The current price of a first class stamp is 47 cents. A domestic first class letter (1 oz.) is 47 cents. The price of each additional ounce is 21 cents. It will cost you 34 cents to send a domestic postcard.
WASHINGTON (AP) â It's going to cost you a few pennies more to mail a letter. The cost of a first-class postage stamp is now 49 cents â 3 cents more than before. Regulators approved the price hike in December, and it went into effect Sunday. Many people won't feel the increase right away: Forever stamps are good for first-class postage at whatever the future rate.