Earth's magnetism demonstrates that:
A) part of Earth's core must be a liquid metal.
B) Earth's core is completely made of nickel.
C) a large part of Earth's crust is made up of metal.
D) Earth's crust is mainly composed of magnetic material.
A
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What is the reason for the seasons on Earth?
a) Earth is cloest to the Sun in July, farthest from the Sun in January b) Earth is tilted with respect to the Sun by about 23.5 degrees c) Earth orbits the Sun more slowly in winter, faster in summer d) Earth rotates more slowly in winter, faster in summer e) Earth's Moon blocks more sunlight from reaching Earth in winter than in summer
An ac source of period T and maximum voltage V is connected to a single unknown element. At time t = 0 the voltage is zero. At time t = T/4 the current in the unknown element is equal to zero, and at time t = T/2 the current is I = - Imax where Imax is the current amplitude. What is the unknown element?
A) a resistor B) an inductor C) a capacitor D) an inductor or a capacitor E) More information is needed to identify the element.
Constellations rise in the ________ and set in the ________.
A. east; west B. morning; evening C. west; east D. evening; morning E. Constellations neither rise nor set.
Which of the following statements about scientific theories is false?
A) Theories are not taken seriously if they contradict older, more developed, theories. B) A theory is a model designed to explain a number of observed facts. C) If even a single new fact is discovered that contradicts what we expect according to a particular theory, then the theory must be revised or discarded. D) A theory must make predictions that can be checked by observation or experiment. E) A theory can never be proved beyond all doubt; we can only hope to collect more and more evidence that might support it.