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Ripple tank | |||
The ripple motor is connected to a variable 6V DC supply. The rippler is lowered so that it just touches the surface of the water and the motor is turned on. Plane waves will move towards the left.(The brown rectangle is the rippler)
By placing a metal bar in the tank and tapping the wooden bar a pulse of three of four ripples can be sent towards the metal bar. The ripples reflect from the bar. If the bar is placed at an angle to the wavefront the reflected waves can be seen to obey the law of reflection. The angle of incidence and angle of reflection[?] will be the same.
If a concave semicircular obstacle is used, a plane wave pulse will converge on a point after reflection. This point is the focal point[?] of the mirror. Circular waves can be produced by dropping a single drop of water into the ripple tank. If this is done at the focal point of the "mirror" plane waves will be reflected back.
If a sheet of glass is placed in the tank the depth of water in the tank will be shallower over the glass than elsewhere. The speed of a wave in water depends on the depth, so the ripples slow down as they pass over the glass. This causes the wavelength to decrease. If the junction between the deep and shallow water is at an angle to the wavefront[?], the waves will refract. In the diagram above, the waves can be seen to bend towards the normal. The normal is shown as a dotted line. The dashed line is the direction that the waves would travel if they had not met the angled piece of glass.
In practice, showing refraction with a ripple tank is quite tricky to do.
If an obstacle with a small gap is placed in the tank the ripples emerge in an almost semicircular pattern. If the gap is large however, the diffraction is much more limited.
Small in this context means comparable to the wavelength of the ripples.
The storm, the ball, the finding of the necklace in
She sat down on a stone by the roadside to think things over, and let
at a loss what to do next.html">next. So she sat still and waited for inspiration.
asters along the road craned their necks to get a look at this great
inquiringly before her.
"I shall sit here," she said aloud, quoting the Frog Footman in
suddenly seemed to Sahwah as if she would like nothing.html">nothing better than to
comfortable, and the sun was so warm and pleasant and the breeze was so
then it began to melt away. Sahwah's head.html">head nodded; then she slid off the
in its cradle.
Mr. and Mrs. James Watterson of Chicago were motoring back to their
papers had been full of the disappearance of Margery Anderson and the
for information concerning her whereabouts. The papers said he had gone
the article with great interest. She did not know the Andersons and she
nothing else to do at the moment, her husband having gone out and left
affair until she knew them by heart.
The next morning, on their way north, they came upon Sahwah sleeping in
stopped the car and jumped out. Sahwah's face was streaked with green
twisted under her head in the peculiar position in which Sahwah always
dangling half out of the pocket of Sahwah's coat and a name.html">name written on
Anderson_. Sahwah had gotten something into her eye the day before,
one--Margery had handed her one of hers. At the sight of that name Mrs.
was fresh in her mind. "It's that Anderson girl!" she exclaimed,
she was unconscious and I believe their idea was to take her to.
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