A recent announcement indicated that magnetic motors can be used to cool refrigerators. In the method, a gadolinium-based warms and cools off in response to application of a magnetic field. The gadolinium rotating wheel is the only moving part
Why might this be a breakthrough?
Moving parts involve friction. Elimination of friction reduces waste of energy. It
remains to be seen whether this is a breakthrough.
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Which of the following ingredients was least abundant in the solar nebula?
A) metal B) rock C) hydrogen compounds D) hydrogen E) helium
Three coplanar parallel straight wires carry equal currents I to the right as shown below. Each pair of wires is a distance a apart. The direction of the magnetic force on the middle wire
a.
is up out of the plane of the wires.
b.
is down into the plane of the wires.
c.
is in the plane of the wires, directed upwards.
d.
is in the plane of the wires, directed downwards
e.
cannot be defined, because there is no magnetic force on the middle wire.
The mass of the Moon is about 1/80th of the mass of Earth. The force exerted by Earth on the Moon is about 80 times that exerted by the Moon on Earth
Indicate whether the statement is true or false
A laser produces a beam of 4000-nm light. A shutter allows a pulse of light, 30 ps in duration, to pass through
What is the uncertainty in the energy of a photon in the pulse? (1 eV = 1.60 × 10-19 J, h = 6.626 × 10-34 J ? s) A) 2 ×10-5 eV B) 2 ×10-6 eV C) 2 ×10-4 eV D) 2 ×10-3 eV E) 2 ×10-2 eV