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Lenses can be used to focus sunlight to a small point to burn paper or dry brush. A person demonstrates this using their own eyeglasses as the lenses. From this you can tell that

A ray of light moves from air into water. Which path most accurately shows the refraction?

An iPod is 20 cm in front of a flat mirror. You see the reflected image and must refocus your eye, perhaps even take off your eyeglasses, because

A fast train approaches a car waiting at a grade crossing and sounds its horn. A person in the car will notice that, compared to what it would be if the train were at rest, the horn sound’s

When a wave reflects from a stationary boundary,

Jim the meteorologist has predicted fair weather all day but sees flashes of lightning followed by rolls of thunder. To calculate the distance to the lightning bolt, Jim should measure the time between the instant he first sees a lightning flash and the

In order for a telescope to produce a large magnification one would select lenses of

Two waves approach each other as shown. When they completely overlap, the resulting wave will look like

Suppose an audible sound wave were being produced at a frequency of 800 cycles per second. If the frequency were doubled, the sound would become

Your bones are playing tug-of-war over calcium levels. Which two hormones are on each side, with one increasing plasma calcium and the other decreasing it?