Consider two copper wires of equal cross-sectional area. One wire has 3 times the length of the other. How do the resistances of these two wires compare?
A) Both wires have the same resistance.
B) The longer wire has 1/3 the resistance of the shorter wire.
C) The longer wire has 3 times the resistance of the shorter wire.
D) The longer wire has 9 times times the resistance of the shorter wire.
E) The longer wire has 27 times times the resistance of the shorter wire.
C
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What is the dynamo model of Earth's magnetic field?
A. Earth's magnetic field changes too rapidly for it to be generated in Earth's interior. B. Earth's magnetic field is maintained by convection in the interior of the planet, as well as its rotation. C. Electric currents in the atmosphere (aurora) generate Earth's magnetic field. D. Currents in Earth's oceans maintain the planet's magnetic field. E. None of these choices are correct.
What of the following most directly determines how much fuel a star has?
A. its density B. its temperature C. its speed of rotation D. its luminosity E. its mass
The magnetic field inside a circular loop of wire of radius 30 cm increases at a constant rate from 2.0 × 10^–3 T to 3.5 × 10^–3 T in 0.47 s. What is the induced emf in the wire?
a. 9.0 ×10–4 V b. 2.3 ×10–4 V c. 1.8 ×10–3 V d. 1.8 ×10–4 V
Which of the following choices best corresponds to what is required by the second law of thermodynamics for any process taking place in an isolated system?
a. entropy decreases c. entropy increases b. entropy remains constant d. entropy equals work done on the system