1  A Few Basic Concepts

Instructions: True means reliably true (unless the item itself indicates it is meant to be an approximation). Untrue means anything else. A compound sentence is true if all its parts are true.

1.

□ True   or   □ Untrue? – In a properly designed experiment, you change only one variable at a time.

2.

□ True   or   □ Untrue? – If you multiply 4.43021 by 2.54 the result should be rounded to 11.3.

3.

□ True   or   □ Untrue? – It is better to use the term “potential difference” rather than “voltage”.

4.

□ True   or   □ Untrue? – Questions about stability should be answered in terms of the minimum-energy principle.

5.

□ True   or   □ Untrue? – For solid materials, thermal energy refers to the random kinetic energy of the atoms and molecules in the material.

6.

□ True   or   □ Untrue? – Absolute zero is the temperature where random motion of the molecules ceases.

7.

□ True   or   □ Untrue? – Hot air rises.

8.

□ True   or   □ Untrue? – Heat flowing into a system raises the system’s temperature.

9.

□ True   or   □ Untrue? – An atom can exist only in certain discrete states. That is, it can leap from one quantum state to another, but it can’t go halfway.

10.

□ True   or   □ Untrue? – Pure water has a pH of 7.

11.

□ True   or   □ Untrue? – During a change of state (e.g. ice melting to water) the temperature remains constant.

12.

□ True   or   □ Untrue? – Molecules are stable particles of matter.

13.

□ True   or   □ Untrue? – Molecules are covalently bonded particles of matter.

14.

□ True   or   □ Untrue? – Molecules obey the law of definite proportions.

15.

□ True   or   □ Untrue? – The F₂ molecule has a single bond, the O₂ molecule has two bonds, and the N₂ molecule has three bonds. Each bond consists of a pair of electrons with opposite spins. In the oxygen molecule, in addition to the bonds, each atom has two lone pairs, as shown schematically in figure 1.

Figure 1: Dot Diagram of Oxygen Molecule

16.

□ True   or   □ Untrue? – There are two kinds of electrical charge. That is to say, the two-fluid model of electricity is right, and the one-component model is wrong.

17.

□ True   or   □ Untrue? – You can estimate the temperature of a flame by looking at its color.

18.

□ True   or   □ Untrue? – There is no such thing as centrifugal force.

19.

□ True   or   □ Untrue? – To model the earth’s magnetic field, take a globe and skewer it with an ordinary bar magnet, putting the bar’s “N” pole in northern Canada, and its “S” pole in Antarctica.

20.

□ True   or   □ Untrue? – All dinosaurs died out millions of years ago.

21.

□ True   or   □ Untrue? – Yeast consists of microscopic plants that lack chlorophyll.

22.

□ True   or   □ Untrue? – Mushrooms are another example of plants that lack chlorophyll.

23.

□ True   or   □ Untrue? – If it lays eggs, you know for sure it’s not a mammal.

24.

□ True   or   □ Untrue? – If it secretes a nutritious liquid from specialized cells to feed to its young, you know for sure it’s a mammal.

25.

□ True   or   □ Untrue? – Eagles are more closely related to foxes than they are to crocodiles.

26.

□ True   or   □ Untrue? – To work properly, an airplane wing must be curved on top and relatively flat on the bottom.

27.

□ True   or   □ Untrue? – If two parcels of air flow past a wing, they move from the front to the back in essentially equal amounts of time, even if one passes above and the other passes below the wing.

28.

□ True   or   □ Untrue? – Blowing a stream of air across the top of a piece of paper is a good way to demonstrate the principle that faster-moving air has lower pressure.

29.

□ True   or   □ Untrue? – Bernoulli’s principle is only valid for incompressible fluids, which means it cannot be trusted for something as obviously compressible as air.

30.

□ True   or   □ Untrue? – Einstein originated the principle that physics is the same even when the reference frame is moving.

31.

□ True   or   □ Untrue? – Einstein originated the idea that the speed of light is the same in all reference frames.

32.

□ True   or   □ Untrue? – Einstein originated the idea of spacetime, i.e. that time is the fourth dimension.

33.

□ True   or   □ Untrue? – Einstein originated the idea of black holes, i.e. objects so massive that light cannot escape from their gravitational field.

34.

□ True   or   □ Untrue? – General relativity explains gravity in terms of the curvature of spacetime, as illustrated by marble rolling inside a bowl, which represents a particle in orbit.

35.

□ True   or   □ Untrue? – No two snowflakes are alike, but each one has perfect or near-perfect sixfold symmetry.

36.

□ True   or   □ Untrue? – A rainbow is composed of seven colors.

37.

□ True   or   □ Untrue? – If you drop a small piece of chalkboard chalk into a cup of acid, a vigorous reaction will occur. Bubbles will be produced. If there is enough acid, the reaction will continue until the chalk is consumed.

38.

□ True   or   □ Untrue? – Ordinary raindrops 💧 falling through the air 💧 exhibit the classic streamlined 💧 shape.

39.

□ True   or   □ Untrue? – The sun rises in the east and sets in the west.