The Sun delivers roughly 1 kW m -2
of power to the
Earth's surface. A parabolic mirror with a 1 m radius is used
to focus this energy onto a beaker containing 1 L of water.
Estimate the time taken by the mirror to raise the temperature of the
water by 50°C, assuming the specific heat capacity of water
to be 4200 J K-kg- and ignoring energy
losses to the surroundings.

they are made of gases.

they have a spherical shape.

they make energy through fusion.

most historians agree that gabriel mouton, the vicar of st. paul’s church in lyons, france, is the “founding father” of the metric system. he proposed a decimal system of measurement in 1670. mouton based it on the length of one minute of arc of a great circle of the earth (now called a nautical mile, 1852 meters). he also proposed the swing-length of a pendulum with a frequency of one beat per second as the unit of length (about 25 cm). a pendulum beating with this length would have been fairly easy to produce, thus facilitating the widespread distribution of uniform standards. over the years, his work was revised, improved, and extended by a number of french scientists.

the political sponsor of weights and measures reform in the french revolutionary national assembly was the bishop of autun, better known as talleyrand. under his auspices, the french academy appointed several committees to carry out the work of developing a usable system of weights and measures for france. one of the committees recommended a decimalized measurement system based upon a length equal to one ten-millionth of the length of a quadrant of the earth’s meridian (i.e., one ten-millionth of the distance between the equator and the north pole).

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